Office of Operations Freight Management and Operations

Comprehensive Truck Size and Weight Limits Study: Stakeholder Sessions 2013-2015: Feedback and Comments, Final Report

APPENDIX A – DISPOSITION OF MAY 29, 2013, EVENT COMMENTS

Session A: Alternative Truck Configurations

Alternative Truck Configurations Breakout - 1

There was a lengthy discussion at the beginning with many questions regarding the template for submitting information to recommend alternative truck configurations.

Question from audience as to what the baseline will be: Answer: for tractor trailers, it will be the 80,000 lb. 5-axle configuration and for double trailer combinations it will be the Surface Transportation Assistance Act of 1982 (STAA) double (twin 28 ft. trailers at 80,000 lbs.)

Will there be 2 different kinds of axle weight? Will you look at 2 different weight distributions for 6 axles? The required options for six-axle tractor semitrailers are: Option (i) 53 ft. trailer: GVW 97,000 lb. Axle weights: 12,000 lb. steer, 34,000 lb. tandem, 51,000 lb. tridem; Option (ii) 53 ft. trailer: GVW 97,000 lb. Axle weights: 12,000 lb. steer, 38,000 lb. tandem, 47,000 lb. tridem

Alternate configuration recommendations from participants:

  • Look at Straight trucks as an alternative configuration
  • Trucking Industry would like to see analysis of Twin 33s (addresses volume)
  • 97,000 lb. vehicle is a “go almost anywhere vehicle” (addresses weight)
  • Look at triples
  • Study weight limitation of 105,000 lb. and 7 axle configuration

General recommendations/comments for the Study:

  • Some States allow 6-axle trucks on non-Interstate roads. In order to develop the data, you would have to look at some non-Interstate operations to reach your conclusions.
  • Participant discussed the I-5 bridge collapse in Washington State. That truck was operating under a State-issued over-size permit and it took down the bridge. That will cost the taxpayers millions plus the extra costs for all travelers for rerouting (in terms of extra fuel and time) to use alternate routes. The costs of larger vehicles and their impact should be factored in. Look at effects of waivers and permitting in terms of the cost to taxpayers.
  • Imperative to study cost impacts of non-divisible loads.
  • When looking at the costs of heavier vehicles, or longer trucks, what about considering the cost savings of using them? Will you look at freight efficiency by truck type?
  • Take input from industry on what configurations to study; their input will be the most relevant.
  • One participant said he was impressed by his sense that the Study team will keep configurations distinct. He has seen others conflate some things as being the same. It is clear that distinct configurations will be studied. One configuration will not be interpreted as another. Some people think that any change will be bad.

There was a lengthy discussion of the bridge formula.

  • How is the bridge formula being addressed?
  • Is the bridge formula being used in the Study?
  • Some of these configurations are not designed to the bridge formula. Panel comment: Methods for studying bridge effect are more developed (up to date) and focus on the structure’s strength state. The bridge formula is used to limit truck weights and is not useful in assessing a bridge’s ability to accommodate certain vehicles.
  • Will the Study look at vehicles that fit the current bridge formula? Answer: the Study will look at both those that meet the Federal bridge and those that do not.
  • Attendee expressed concern that the study of bridges has advanced; however, the bridge formula is a frame of reference for people reviewing your product.
  • If you are studying impact, you need to start with the fact that the Interstate was built to certain specifications.
  • If you will study something that does not meet the current bridge formula, you should make that very clear.
  • Address how the configurations studied relate to the bridge formula.

The attendees were asked if there were any comments on tire options – No comments were received to the question but earlier the following comment was recorded:

  • Wide tires have effect on safety, fuel economy.

Key Elements for Selection

  • Access to routes, trucks are not just on the Interstates, look where else they are operating.
  • Make the configurations studied as useful and practical as possible, need to hear from industry
  • One consideration for all three of the alternative configurations should be stopping distance at normal highway speeds as compared to current vehicle configurations. Any new configurations should have comparable stopping distances at highway speeds.
  • Need to define what the "old" configuration is. It is 5-axle, 80,000 lb. tractor semitrailer.
  • Look at prior studies to see if the technology and equipment has changed today and base any changes on data.
  • Parking – where will longer vehicles park on the side of the roads?
  • What if you come up with a vehicle that is not practical for non-Interstate roads? How will these vehicles traverse? How do States manage this?
  • Configuration compatible access with different classes of roads.
  • A lot of States allow reducible loads off the Interstate. You should poll the states to see what the number is. With a lower amount, they are able to traverse anywhere.
  • Are you considering increased rollover risk? Panel Comment: The public perception is that heavier loads result in higher rollover risk. This is a complicated issue and there are data suggesting that good policy can result in heavier vehicles without compromising rollover risk. We will be investigating this issue in the safety analysis.
  • There are studies that looked at the interaction between infrastructure and vehicles with a higher center of gravity. Others commented that the center of gravity depends on the cargo/load. There is an issue if you allow larger vehicles; the operator might not have a higher density vehicle to match the load.
  • From FMCSA: truck parking is important because of the hours of service. If the driver cannot park his larger truck, he cannot operate. Currently doubles and triples are parking on the sides of the ramps. It was noted that there is a truck parking capacity study currently underway but it is not considering LCVs.
  • Regarding Accessibility: Need to consider enforcement. Illinois had a two-tiered system and it was very complex for industry and enforcement to understand the access laws off the Interstate. Do not make it overly complex for industry and enforcement to understand the accessibility rules.
  • Some States may not buy in to the 97,000 lb. 6-axle tractor trailer configuration.
  • There are currently variations and any changes could impact the States.

What are the benefits of these elements?

Industry input is required to gain an understanding of what would be the most useful and widely used vehicle options and the benefits that could flow from them.

What are the disadvantages of these elements?

None were stated by participants.

The attendees were asked what other areas should be considered when selecting alternative configurations. The following list was produced based on attendee input:

  • Training for operators.
  • Impact on public safety, traveling public not knowing how to drive around these new vehicle configurations.
  • Energy and environmental impacts; Environmental - fuel use, fuel savings, trucks taken off highway due to new configured trucks carrying more cargo - need less vehicles.
  • Economic impacts.
  • If it becomes more efficient to ship by truck, this could increase the number of trucks on the road since it is cheaper to ship by truck than by rail.
  • Efficiency.
  • Congestion.
  • Consider if trailers will need to be modified. Counterpoint: Trailer configuration – assume whoever is using trailer, if they can get the appropriate rating what does this matter with regard to the Study?
  • Consider if the tractor will need to be modified to haul the heavier loads.
  • Consider at what speeds these vehicles can safely operate. Look at vehicle speed in context of stopping distance.
  • What about data translation?
  • Should also consider how to make States more uniform. The trucking industry would like this.
  • What about tire usage issues? Dual vs. wide single.

Alternative Truck Configurations Breakout - 2

This group also questioned what the baseline will be. Answer: 80,000 lb. 5-axle configuration for tractor semitrailers and STAA 28 ft. doubles for multiple trailer configurations.

Alternate configuration recommendations:

  • Use 3-axle single units with one steering axle and 2 drive axles (cargo vans). This could also be used as a baseline to compare safety and wear and tear.
  • Use SU7 – this is a single vehicle, which is a specialized flat bed, open box with 7 axles. (Recommendation from a State DOT representative)
  • Use a vehicle with a "spread axle" (referred to as split tandems, which carry 20,000 lbs. on the two axles, spread 10 ft. apart totaling 40,000 lbs. instead of 34,000 lb. standard tandem) which is the type of vehicle he drives. With this type of axle, he can carry more weight. The advantage is that the distribution of the load is shifted to match the equipment. Use the California Bridge law rather than what is legal in other states. (Truck driver recommendation)
  • Use a 53 foot "step deck" configuration van can fill with more low density items and still haul within legal limits, lowers the center of gravity (even with high density cargo). The step is approximately 21 inches. Configuration can fit more cubic feet within this configuration (volume vs. weight). (independent truck driver recommendation)
  • The 38,000 lb. tandem is of interest to the forestry/logging industry. (Forestry representative recommendation)
  • Use a uni-body truck with 2 axles in front and 3 in back. This vehicle can be made wider with more axle weight as compared to a truck with multiple trailers and still hold within its lane. This type of truck is operating in Spain. Something similar is operating in Israel. (www.truckingvideo.com)
  • Look at congressional intent, focus on what Congress is being asked to enact. Also recommended studying Twin 33, Rocky Mountain and Turnpike 53 ft. doubles and triples with 28 ft. trailers. Another audience member commented they thought the 6-axle 97,000 lb. configuration was a big focus in Congress.
  • Twin 33 would be their first choice; this is of particular interest to the Less Than Truckload (LTL) sector. Triples would be the second choice. (Trucking Association recommendation)
  • Agreed with Twin 33 and Triples being the top choice. No clear choice from either of them on the third pick. There was no clear preference between the two types of doubles. Some thought there would be more data for Rocky Mountain doubles in the United States. If using data from Canada, Turnpike doubles would have more miles. (Truck Safety advocate)
  • 5-axle configuration with weight up to 100,000 lbs.

General recommendations/comments for the Study:

  • Do not use any data from Europe as their regulations with regard to speed, Hours of Service, etc., are very different from the United States. Mexico and Canada should be part of the Study since freight runs from Mexico to Canada.
  • Recommendation from a State bridge engineer: Include axle weight and spacing. With whatever configuration is studied, axle weight and spacing information is needed. Also important is tare weight and payload. Need to know what the increase in weight is associated with and how efficient the vehicle is in terms of the freight task. Is most of it going into the vehicle (for the extra axle for example) or into the payload.
  • Recommended looking at each configuration to see where the weight will be used. Will weight be added to vehicle to increase driver safety and comfort, or just about adding cargo weight?
  • If you increase spacing, axle weights – each one has an impact on many things such as safety, infrastructure, and maneuverability.
  • Any analysis should include input from at least a couple drivers that have 20 years of experience. Increasing the number of doubles/triples would impact safety significantly. When studying alternative configurations you need to study the effects on all other aspects.
  • Keep in mind that drivers who operate 97,000 lb. trucks are more experienced drivers – if this becomes a standard, will have drivers with less experience driving these. The analysis needs to control for driver experience.
  • Get input from truck drivers.
  • When interviewing drivers, only interview those that drive the configuration in question.
  • You need to understand that every change that is made from the existing 5-axle 80,000 lb. configuration will reduce safety. How much safety are we willing to compromise?
  • Do not give credence to emotional appeals – use data not emotion. Use a science-based approach.
  • Need to consider diversion of large loads. For example, 100,000 lb. non-divisible container comes out of port; the logistics person can divert it so it does not go by any scales. Question and discussion about whether the configuration would be different since international containers are transported on 40 ft. chassis not 53 ft. chassis.
  • Consider diversion in the Study and also the migration back to good roads if they did not feel the need to divert.
  • Look at unbalanced loads.
  • Look at as broad a network as possible, not just the Interstates. Noted example in Illinois where they have 9,000 bridges within 10 miles of the Interstates.
  • Consider accelerated depreciation to implement the new equipment.
  • How does taxation play into this?
  • Component of Network Access: there are routes that are and are not used due to reasonableness of cost factors (example, toll roads).
  • Look at infrastructure impacts in terms of if you increase the weight by 20 percent. The results are X.
  • Are you looking at modal diversion? Getting more traffic away from rail, if so then there will be an increased impact on infrastructure. Will you assume that rail will not lower rates to counteract the shift?
  • Use recent studies, no older than 5 years
  • The 2000 Comprehensive Truck Size and Weight (2000 CTSW) Study was a good study – methodology was very good, could be useful. Additional point: Recommend reviewing the 2000 CTSW Study for any benefits or weaknesses of that study.
  • One person noted a study (did not give study name) that looked at where truck and rail are competitive.
  • Assess rate of adoption.

Key Elements for Selection

  • North America, North American Free Trade Agreement (NAFTA) area.
  • What Congress wants?
  • Who uses the configurations to be studied, especially the last 4 on the graphic (LTL)?
  • Practicality.
  • Impacts on economy.
  • Safety – focus on road safety and effects on guardrail or cable barrier.

Vehicle Configurations Distilled from the Listening Sessions

Following the FHWA May 29, 2013 input session, the table that follows is a proposed list of vehicles to be studied.

Main points –

  1. Since the 6-axle tractor semitrailer at 97,000 lbs. does not comply with the bridge formula, include a variation that meets the bridge formula (approx. 91,000 lbs.) (Note: although this configuration was selected to represent a 6-axle vehicle that would be compliant with the bridge formula, the spacing on the rear tridem axle set for the vehicle used in the Study did not meet the consecutive axle test of the bridge formula.)
  2. The LTL Industry strongly supports twin 33 ft. double at current 80,000 lb. limit. Suggested variations, examine this unit at 80,000 lbs. and at bridge formula limit in both the A and B configuration.
  3. Include an analysis of triples trailers (meeting the bridge formula) in both the A and B configuration.
  4. Include turnpike doubles consisting of twin 53 ft. trailers in the A-configuration only. This configuration uses currently available standard trailers.
  5. Use the permitted STAA 28 ft. doubles as a reference control for the double combinations.

Table 2. Truck configurations – generic renderings.
Truck Configurations Generic Renderings
5-axle tractor 53 ft. semitrailer 5 axle tractor with semitrailer
Option (i) 53 ft. trailer: GVW 80,000 lb. Axle weights: 12,000 lb. steer, 34,000 lb. tandem, 34,000 lb. tandem (Control)
Option (ii) 53 ft. trailer: GVW 88,000 lb. Axle weights: 12,000 lb. steer, 38,000 lb. tandem, 38,000 lb. tandem
6-axle tractor 53 ft. semitrailer * 6 axle tractor with semitrailer
Option (i) 53 ft. trailer: GVW 97,000 lb. Axle weights: 12,000 lb. steer, 34,000 lb. tandem, 51,000 lb. tridem
Option (ii) 53 ft. trailer: GVW 97,000 lb. Axle weights: 12,000 lb. steer, 38,000 lb. tandem, 47,000 lb. tridem
Option (iii) 53 ft. trailer: GVW 91,000 lb. Axle weights: 12,000 lb. steer, 34,000 lb. tandem, 45,000 lb. tridem (Bridge)
Short doubles Twin 28 ft. or twin trailers
Twin 28 ft. trailers: GVW 80,000 lb. Axle weights: 12,000 lb. steer, 17,000 Drive, 3 x 17,000 trailer axles (Control)
Twin 33 ft. Trailer Combination twin 33 ft. trailer combination
Option (i) Twin 33 ft. trailers: GVW 80,000 lb. Axle number and weights to be determined (low density)
Option (ii) Twin 33 ft. trailers GVW Bridge limited. GVW, axle number & weights to be determined (high density)
Evaluate as A and B configurations
Turnpike Doubles twin 53 ft. double trailers
Twin 53 ft. trailers: Bridge limited. GVW, 9-axle weights to be determined – A-configuration only
Triples triple trailers
Option (i) Triple 28 ft. or 28 ½ ft. trailers: GVW 105,500 lb. 7-Axles (low density)
Option (ii) Triple 28 ft. of 28 ½ ft. trailers: GVW 129,000lb. 9-axles (high density)
Evaluate as A and B configurations
Note: Renderings are not to scale.
GVW = gross vehicle weight

Session B: Data, Models, Methods (Breakouts 1 & 2)

Table 3. Data, models, and methods (breakouts 1 & 2).
Topic Comments Disposition
Pavement Data Sources
Look at Wisconsin Study 2009. The 2009 Wisconsin Study was included in the relevant Desk Scans.
A 2012 Virginia Department of Transportation (VDOT) Study on pavement costs as a function of axle weights included all road systems. VDOT will send it to FHWA. Because data required to assess a change in truck size and weight changes on local roads was not available on a national basis, the discussion of impacts on local roads was limited to a qualitative assessment in the Study.
Maine, Minnesota, and Vermont Studies all included analysis of actual larger truck pavement effects. Maine and Minnesota used Equivalent Single Axle Load (ESAL) assumption, and Vermont uses distress Load Equivalency Factors. These are outdated tools; the Study used the latest pavement assessment capability available through AASHTOWare® Pavement ME Design.
Some previous studies have been done with preconceived conclusions. We should only use independent analyses. In conducting the Desk Scans, any bias evident in previously completed work was accounted for and controlled in cases where it was used in the conduct of the Study.
Some previous pavement studies are great scientifically, but would have resulted in permit fees too great for the trucking companies to absorb. If we need to charge more, the fees need to be practical. Recommendations on setting user fees or permit fees were not relevant to or included in the Study.
Pavement Models and Methods
Look at the Vermont study and figure out a way to apply the approach nationally while accounting for differences between States and scale. In the Desk Scan phase of the project, the Vermont Study was considered; the latest pavement models were employed in analyzing impacts on pavements in the Study and were not available when the Vermont Study was conducted.
Use the Pavement Damage Assessment Tool (PaveDAT) model to analyze differences in specific truck configurations. National Pavement Cost Model was used to allocate costs; to the extent costs were allocated within the Study, not directly to assess pavement impacts. PaveDAT did not yield any value in doing so.
The team should evaluate different types of pavement. There are key differences between rigid and flexible pavement. We analyzed both types of pavement in the Study. Differences in the performance of rigid and flexible were understood from the outset.
Make sure to validate any use of past study results to see if they used the same kind of pavement we do today. We did not directly use any previous study results.
Ensure that cost of pavement damage includes costs imposed on trucks by poor quality pavements. Impacts on other highway users are beyond scope of this Study.
Consider that the biggest pavement impact will be off the Interstate System, including on local roads, ramps, and connectors. We sought to include all highway systems in our analysis. (Note: Although it was originally intended, non-National Highway System (NHS) roadway sections were not included in the Study due to data availability challenges).
Pavement Impacts
The Study should look at western mountain passes. Trucks traveling through the mountains tend to be heavier, and there are examples in all environmental conditions from snow to rain to desert. Trucks braking downhill also cause more damage. We included a full range of environments and traffic conditions in the Study, but our pavement models do not include braking effects.
Look at wet areas particularly since pavements are less stable in wet conditions. We included a full range of environments in the Study.
Egress/ingress issues will affect pavement impacts. We looked at all highway systems. (Note: Although it was originally intended, non-NHS roadway sections were not included in the Study due to data availability challenges).
Use Weigh-in-Motion (WIM) results to focus our efforts on roads that have a significant amount of overweight vehicles to guide our analysis. We included a full range of traffic levels on the NHS. Consideration of shoulders, curbs, and damage due to braking forces and or the static weight of stopped trucks was beyond the scope of the study.
Include damage to shoulders and curbs, and look especially at stoplights for damage caused by sitting and stopping trucks. Shoulders were included in our pavement damage cost assessments; curbs were not due to the Study focus.
Take pavement sections from the right lane and compare it with left lane-- there are obvious differences in how much wear there is where the trucks travel. Ample empirical evidence showed that trucks cause damage. Our damage models looked at the lanes truck use.
Consider distribution of weights to each axle. Uneven loading has different impact than uniform loading. We used actual observed axle weights as basis for our analysis.
Existing conditions need extensive data for accuracy, but we have a limited number of WIM sites, and limited knowledge of truck types and how they might be operated. The data that FHWA compiles from the States through the Traffic Monitoring Program was used as the primary data source for conducting analysis in this area of the Study.
The Study should look at western mountain passes. Trucks traveling through the mountains tend to be heavier, and there are examples in all environmental conditions from snow to rain to desert. Trucks braking downhill also cause more damage. We included a full range of environments and traffic conditions in the Study, but our pavement models do not include braking effects.
Look at wet areas particularly since pavements are less stable in wet conditions. We included a full range of environments in the Study.
Egress/ingress issues will affect pavement impacts. We looked at all highway systems. (Note: Although it was originally intended, non-NHS roadway sections were not included in the Study due to data availability challenges).
Use Weigh-in-Motion (WIM) results to focus our efforts on roads that have a significant amount of overweight vehicles to guide our analysis. We included a full range of traffic levels on the NHS.
Include damage to shoulders and curbs, and look especially at stoplights for damage caused by sitting and stopping trucks. Shoulders were included in our pavement damage cost assessments; curbs were not due to the Study focus.
Take pavement sections from the right lane and compare it with left lane-- there are obvious differences in how much wear there is where the trucks travel. Ample empirical evidence showed that trucks cause damage. Our damage models looked at the lanes truck use.
Consider distribution of weights to each axle. Uneven loading has different impact than uniform loading. We used actual observed axle weights as basis for our analysis.
Existing conditions need extensive data for accuracy, but we have a limited number of WIM sites, and limited knowledge of truck types and how they might be operated. The data that FHWA compiles from the States through the Traffic Monitoring Program was used as the primary data source for conducting analysis in this area of the Study.
Consider full range of roads, including pavements on local roads. We intended to include all highway systems in our analysis. Ultimately, non-NHS roadway sections were not included in the Study due to data availability limitations.
Consider the confidence level of not having enough data. This was considered and results were presented in alignment with confidence levels.
Bridge Models and Methods
Watch out for bridges designed for old standards and not rehabilitated (they don’t even meet current load). A full range of bridge construction dates were considered in selecting bridges analyzed. Bridges that require posting were specifically assessed and reported in the findings generated through the analysis.
Ages and design loadings of the bridges in the sample of 500 bridges should match inventory distribution of actual bridges. This step in selecting samples was conducted and described in the Technical Report.
Bridges on the Interstate System have different design loadings than bridges off the Interstate System. All bridges designed and built in the last 50 years on the NHS, which includes the Interstate, follow guidelines from AASHTO. Bridges designed and built off the NHS can use State specifications. All bridges, regardless of system, are load rated for the legal and unrestricted permit vehicles that use them in each State. When a bridge’s load rating is not adequate for those vehicles, it is posted or restricted for load.
Consider original and current design loadings and ratings. We considered loadings for the current truck fleet as well as the future truck fleet and estimated truck travel levels, known as the scenario traffic, from the Modal Shift Analysis.
Consider deck and substructure separately. The AASHTOWare® Bridge Rating (BrR) assesses the structural performance of bridges including superstructure. Bridge decks were not assessed due to the lack of generally accepted modelling tool. The development of such a tool is recommended as a finding reported in this Study.
Watch for static load issues, with peak hour and construction equipment on bridges like the I-35 bridge collapse. The AASHTOWare® BrR software used in the Study accounts for static loads, dynamic loads, and truck trains. Construction staging issues are outside the scope of the Study.
The team should load test bridges in the field (ambient field loading). This recommendation was outside of the scope of the Study. Studies conducted by others where this was performed were considered as part of the Desk Scans phase of the Study.
There is not a complete dichotomy between the hypothetical bridge models and real experience. Some States allow our hypothetical configurations, so why live in a hypothetical world? Maine study, for example, showed little effect. Vermont’s bridges are built differently, however, so be wary of extending those results or we may have an apples and oranges situation. This was designed to be a national study that looked at regions and corridors with similar trucks in the current fleet. An alternative truck type of 97,000 lb. vehicles and other longer combination vehicles were studied to better understand the current conditions compared to the potential impacts of alternative configurations.
Be careful not to extend special conditions in one State to other States. States with similar trucking issues were studied as a region.
Use instrumented bridges whenever possible, especially where study configurations are operating. Existing studies on instrumented bridges were used when possible.
Bridge Impacts
Larger vehicles mean larger risk for catastrophic failure (I-5 in Washington, for example). The bridge impact analysis looked at truck weight issues. Size issues came into play with trusses that have both horizontal and vertical limitations and need to be looked at on a case-by-case basis. Such an assessment was not included in the Study since it is very site-specific.
The Study should include effects on delayed traffic from catastrophic failures. This assessment was not included in the Study as it is very site-specific and not feasible on a national scale.
The Study should include the costs of decks and substructures. Following thorough investigations, a generally accepted bridge deck deterioration model was not identified. For this reason, deck assessments were not completed in the Study. A recommendation that analytical tools be developed to assess bridge deck interactions with heavy trucks was included in the Study’s findings.
We should consider bridge measurements under actual traffic, and how much faster a bridge will deteriorate in ratings under heavier truckloads. Technical analysis was conducted using in-use bridges and traffic that they accommodate along with the scenario traffic estimated as alternative configurations were evaluated.
The legislation may allow individual States to make decisions on whether to allow heavier six-axle trucks, rather than requiring their use. This will result in a patchwork of rules and potentially could force some States to adopt the rules of their neighbors, but will result in lower bridge costs than if all States adopted the new standards. Ultimately, the scenarios (vehicles and networks on which they operate) developed assumed size and weight impacts on a national scale. No State-option scenarios were tested in the Study. State options were interpreted to be out of scope for the Study.
Last-mile routing of heavy loads must be made to protect bridge infrastructure off the Interstate System. The analysis of structural strength of the bridges assessed in the Study considered bridges both on and off the Interstate System.
Trucks on oversize or overweight waivers cost taxpayers money. Bridge failure on I-5, for example, imposed costs on other users in the form of extra hours and miles of travel. Assessing such events is site-specific and not well-accommodated in a study of nation-wide impacts.
General Configuration Issues
There are three parts to this formula: cargo weight, cargo volume, and axle/trailer configuration. All three components figured in the selection of configurations to include in the Study.
Separate weight of truck from weight of cargo. The Study sought to look at both gross vehicle and net cargo weight, as applicable.
We should work to maximize existing volumes and capacities-- low-density cargo could benefit from belly loading with existing limits. The action recommended was outside the scope of the Study.
Take a look at the real world and how heavy some intermodal containers are now. The Study sought to use actual, observed truck weights in the analysis. This proved challenging due to data limitations.
Consider lowering weight from 80,000 lbs. to 70,000 lbs. if we really want to improve safety. MAP-21 directed a study of heavier trucks in comparison to legal weight vehicles. Lighter-weight trucks were outside the scope.
Consider wider trucks, since adding width allows a higher safe center of gravity. Configurations for inclusion in the Study did not specifically address extra width vehicles. This did not prove to be a priority for those expressing interest in specific alternative configurations.
Always keep in mind the cost to taxpayer. The Study focus related to the cost of the infrastructure.
The last time higher weights were considered, the prior studies proved we have a lot of data available and that is how they settled on 80k lbs. and design standards. We should start there. The 80,000-pound truck was used as a control vehicle in the Study.
Operational Impacts
Include operational aspects--roadway geometry, barriers, and turning lanes-- in study. To the extent possible, these factors were included in the Study, as appropriate. Barriers were not assessed due to the limitations of current modeling tools. Updating tools used to assess heavier truck impacts on median barriers and guard rail are recommended as a finding in the Study.
Modal Shift
Reflect the fact that a change in load height can also change modal choice. Load height was not assessed due to the impracticality of delivering all changes to the highway infrastructure needed to accommodate trucks with increased height.
Larger shippers can consolidate loads more readily than smaller shippers. Remember that partially loaded trucks are common. The distribution of operating weights and the extent to which many trucks are only partially loaded was reflected in the truck weight data used.
Historically, heavier trucks means more trucks. Previous studies support this finding, so we cannot assume fewer trucks. The base case and scenario case(s) assumed for simplicity that the same overall volume of freight would be transported by all modes and redistributed traffic among modes and vehicle configurations according to a total logistics cost-based model in the mode shift area of the Study.
Truck ton-miles should not be used as an evaluation tool, trucks are not rail. Truck ton-miles proved to be a useful metric for some aspects of the Study.
Factor in trip distances -- railroads should be used for longer and heavier freight trips. Traffic assignments to modes and configurations were made on an origin-destination basis accounting for variability in trip distance.
Many well-documented modal split models are available, but some assume that all trucks are full (which they are not). We did not assume all trucks were full. The truck weight data used in the Study, where possible, was valuable in understanding loading.
The Study team should interview shippers. The Study team considered soliciting input from shippers as well as other segments of the freight transportation industry. The project schedule did not enable Study Team to conduct such time-intense activities.
Structural shifts within trucking industry (concentration) affect modal choice. The Study did not forecast geo-spatial structural changes in the trucking industry; this was beyond the scope.
Look at GAO 11-134-- A Comparison of the Costs of Road, Rail, and Waterways Freight Shipments That Are Not Passed on to Consumers. This Study was included in the Desk Scan phase of the Study.
Detention times affect costs, and are a function of how much freight you need to load and unload. This is a larger issue for independent drivers than for larger fleets. Assessing the impact of detention times on trucking operations was not within the scope of the Study.
The Study should not just look at total logistics costs, but look at before and after case studies of locations where they have increased weight limits--in some cases, the shippers’ prices stayed the same. The Study focused primarily on freight transportation costs, not shipper prices.
The team needs to understand how goods actually get from place to place. It is much more complicated and detail oriented than previous studies have assumed. Cannot assume perfect operations-- what are the actual practices and challenges? The point was understood and, to the extent practical, used in the Study.
Ideally, we should look at each configuration as a separate scenario, so we can isolate the effects of each, but there are practical constraints. The Study reflected this recommendation.
Build in behavioral factors in modal choice analysis-- do not assume a strict cost-based choice basis. The modal shift analysis did not include any behavior-based factors in modeling shifts among truck types or between modes. Choice and shift was driven by logistics costs.
There are many types of shifts, not necessarily just between the modes. Which configurations are used? How can trucking operations be more efficient and competitive? Estimating shifts among different truck configurations was a key requirement of the Study. The Study focused on the impacts that various alternative configurations could be expected to generate; it was not intended to develop strategies to optimize operations.
Everything is not a truck to rail shift. Truck-to-truck shifts were estimated in the Study as well as truck-to-rail shifts.
Is there a way to account for traffic that would not shift (paper for example)? Each commodity has its own unique set of cost parameters that affect mode and configuration choice. This consideration was included in the modal shift analysis portion of the Study.
Remember the very short truck trips-- a large share of trips are not county to county, but within county. This was considered and, within the constraints of the modal shift model used, reflected in the modal shift analysis area of the Study.
Prior DOT studies have a lot of data and analysis. We should use these studies as a start. The Desk Scan phase of the Study was conducted for that purpose.
Virginia did a freight study a few years ago that we should look at. The Virginia study was included in the Desk Scan phase of the project.
Consider that there are already many State exemptions for certain commodities, some of them seasonal. These were included in the base case to the extent that they are reflected in truck weight data used in the Study.
Safety Data Sources
Some fleet data is available from current LCV operations in Western States and we should use it. Fleet data was considered for use in the Study but was not ultimately used due to its adequacy in fitting the analytical needs of the Study.
The State of Florida has a database that combines crash and permit data. Florida data was considered but did not meet the needs of the Study as stated in the comment.
There are some crash data for truck weights. Trucks Involved in Fatal Accidents (TIFA) provides fatality data by weight up to 2005, but we only know data for weight at time of crash, based on what trucking company reported. TIFA sources are extensive and were included in the Study where appropriate.
Multi-trailer crashes are noted in TIFA reports. Noted.
VMT data by weight and configuration is more difficult to obtain than is crash data, but we need VMT data to calculate crash rates. Carrier data may be available. The Study team considered this to the extent possible and appropriate to the Study.
States may have to change accident reporting processes. Virginia, for example, will change their reporting to better report crash data and capture weight info, but changes in processes will not be done in time for this Study. The Study was based on existing, available data and this area was identified as suffering from a lack of data; this was noted in the findings generated from the Study.
We should look at studies in other countries This was done in the Desk Scan phase of the Study.
There are problems with the current Motor Carrier Management Information System program in capturing fault. Even a parked truck can show up as a crash-- the system is flawed. Noted.
Safety
The team should look at driver and other fleet characteristics (policies, logs, equipment, etc.) when analyzing safety. The team could get some of this data voluntarily from associations. The Study included driver factors to the extent possible where relevant in the Safety analysis area of the Study.
If we use Web data collection, look out for hackers. Noted.
Perhaps, there could be an endorsement process for new weight and limits and configurations that would create a system of checks and balances. Solicitation of endorsements for changes in truck size and weight limits is outside the scope of this Study.
The analysis should account for fleets that use various crash-avoidance technologies, speed limiters, etc. If there are higher limits more generally, the firms that take advantage of the greater weights might not adopt all the crash-avoidance technologies. Any fleet study will attempt to account for all factors that affect crash probability, including technologies, to the extent they are present in data sets used in the Study. Evaluation of safety technologies is not within the scope of the Study.
Are the States with new higher weight limits collecting data? Idaho, Michigan, and Washington were the sources of such data used in the Study.
The Study should look at United Kingdom’s (UK) experience with bigger trucks, but should realize limitations in using the data. European trucks are speed regulated, hours of service are less, and piecework is illegal, for example. If looking at non-U.S., consider all the differences. Differences between the United States and the European Union or other international entities are described in the research.
The Study should look at how heavier and oversized trucks interact with roadway safety infrastructure (guard rails, etc.). Current testing of median barriers and guard rail are cited in the recommendations as needing updates and improvement.
If weight increases, it may overwhelm driver protection, and increase collision severity. The evaluation of truck crash severity data included this factor to the extent that crashes involving over-weight permitted load movements reflect this situation.
The team should evaluate safety on a ton-mile basis since trucks might carry 20percent more cargo. This is how rail safety is evaluated. Ton miles was a metric used in the Study, where it was relevant.
Current system undervalues effect of driver training and experience. Driver factors were accounted for to the extent that available data enabled such an assessment.
Truck safety should be held to a very high standard, especially for heavier trucks, since heavier weights are optional. The safety Study identified the safety effect of alternative configurations and account for the effect of other factors.
Ideally, for safety, trucks need to be lighter and slower. Technology would also help, however, paying drivers by the hour and not by the mile would make the biggest difference. Driver pay is outside the scope, though it was considered in the fleet analysis.
Look at vehicle wear and other impacts as a function of weight (tire and brake wear, for example, and component design). The inspection data evaluation looked at the association of violations in critical mechanical systems related to operating weight.
Dynamic performance
Truckingvideo.com/SafetyTruck has an online video that covers stability of trucks and considers the effects of uneven loads. The video was reviewed as part of the Crash/Safety Desk Scan work.
Vehicle Braking
Engine horsepower is a major part of the truck braking systems. Heavier trucks must be built with bigger engines to keep their ability to stop, since engines and technology are as important as brakes in stopping trucks. Horsepower and carrying capacity were evaluated in the modal shift analysis and used in the fuel consumption and air quality areas of the modal shift analysis.
Talk to truck manufacturers. What does it take to change vehicles and maintain safety? Also, talk to mechanics and component manufacturers. In the simulation analysis conducted, appropriate braking power was assessed.
Driver Certification
The Study team should interview experienced truck drivers (more weight means more responsibility). The Study schedule did not lend itself to conducting widespread interviews. The research team sought input from a trucking industry expert for specifics on driver certification.
Driver experience is important. Current operations pick experienced drivers. If use became widespread, it would bring in less-experienced and brand new drivers to operate the larger equipment. Driver age was included in the analysis of violation and citation analysis conducted as part of the Crash/Safety area of the Study.
Seek opinions and data from drivers about effects of higher weights using a voluntary response option--perhaps from the trucking satellite radio station and/or using the crowdsourcing software from IdeaScale, since FHWA mentioned that they cannot get Office of Management and Budget (OMB) clearance to survey drivers within the time limitations of the Study. The Study schedule did not lend itself to conducting widespread interviews. The research team sought input from a trucking industry expert in the relevant areas of the Study.
FMCSA has driver data/scorecards. The Study did not extensively evaluate driver issues.
The team should look at the results of a FMCSA recent listening session on new entrant standards. The quality of drivers and the details on driver regulation have large impacts on safety. The violation and citation analysis conducted as part of the Crash/Safety area of the Study looked at driver age as a safety factor.
Drive cams could be effective safety devices. The effect of driver monitoring was considered out of the scope of the Study.
Network Considerations
We should consider the most effective network for each configuration rather than assuming universal operation. We should focus logical economic analysis of where and how each configuration should be used and not simply assume using a configuration throughout a corridor where we might have to replace 15 bridges. We considered the extent to which each configuration could operate on different parts of the overall highway network and identified those types of highways suited for each configuration from a safety and geometric perspective.
Fleet Size Issues
When standards are increased, small fleets and independent drivers have to adapt all of their equipment immediately, or they have to turn down loads, whereas larger companies only need to convert 10 percent to 15percent of their fleets. The analysis assumed and measured the impacts at the point of full adoption of any of the alternative configurations studied. Estimating the time span to reach such a point was not included as part of the Study.
How much does it cost to be safe? Cost of safety is greater for independents. This issue can be discussed qualitatively, but a quantitative analysis of the issue was beyond the Study scope.
Permit Operations
The team should consider permitted and illegal overloads separately. This was assessed in the Crash/Safety area of the Study.
Current Federal legal limits include operations above 80,000 pounds through grandfather rights and provisions for special permits, so it is hard to separate legal and illegal loads based on observation. Noted; the researchers encountered this challenge.
Environmental impacts
Environmental and economic impacts are mentioned in legislation but do not seem to be reflected in the Study plan. Environmental, energy, and economic impacts were estimated based on estimated modal shifts caused by each of the alternative configurations assessed.
Look at the expressed values on the DOT Web site, where it implies that we should be moving away from the highway mode toward a more balanced system. We should be asking what would happen if we lowered weights, rather than raising them. This was outside of the Study’s scope.
Look at environmental and fuel consumption impacts. Environmental and fuel consumption impacts were examined in the modal shift area of the Study.
Parking
Truck stops will incur added costs for turning radii and other costs. This was not extensively researched due to data limitations.
Longer configurations will have special parking demands limited by current capacity and geometry. This was not extensively researched due to data limitations that prevented a national analysis.
Highway design standards
Consider costs of changes to ramps, roadway geometry. Configurations and the networks they were envisioned to use were selected based partially on whether they could operate within existing roadway geometry.
Bridge Formula
Bridge formula in the 1980s was based on how bridges were built. It was a scientific formula, and we should revisit how it came to be and the reasoning behind it before we abandon it. The bridge formula has not been part of the bridge design standard specification used in the U.S. It was addressed in the Study as a factor for enforcement effectiveness in the compliance assessment area of the Study.
Enforcement
Look at out of service violations as a function of weight. This assessment was completed in the Crash/Safety area of the Study.
Look particularly at the rate of bridge posting compliance. Compliance with bridge weight restrictions was not included in the Study as it is considered out of the Study’s scope.
Interview police officers and weight enforcement officers as part of this Study. Input from the Commercial Vehicle Safety Alliance (CVSA) informed and contributed to the Study.
Turn drivers into enforcer-- now shippers can overload axles and driver is held responsible. This aspect is outside the scope of the Study.
More trucks imply either a need for more enforcement effort and staffing or lower enforcement rates. This point was assessed in the compliance area of the Study.
The FMCSA crash study underway will send FHWA citations of congressional studies concerning this issue. We currently have very low rates of truck inspections. Data from this FHWA/FMCSA Study was used in the safety/crash area of the Study.
Look at percentage rates of waiver approvals, when waivers can be issued, annual vs. trip permits, and cost of not enforcing. Truck inspections were a factor for evaluating enforcement efficiency.
Go to States that grandfather trucks to find out how they run their programs, what kinds of special driver requirements, maintenance schedules, etc. are in place. States with grandfather exceptions were included in the Study.
Obsolescence of Older Equipment
If truck weights increase, what happens to intermodal? We will need chassis upgrades and perhaps other intermodal equipment modifications. An assessment of intermodal chassis needs is outside the scope of the Study.
ITS Can Improve Safety
Must focus on human factors. Technology can fail, which adds stress to drivers. These areas were outside the scope of the Study.
A major source of stress to drivers is that electronic devices do not record detention time, so those hours count against hours of service requirements. This is going to be aggravated by new hours of service requires and potentially increased detention times with increased size/weight. The comment is outside the scope of the Study.
AASHTO = American Association of State Highway and Transportation Officials • BrR = bridge rating • CVSA = Commercial Vehicle Safety Alliance • DOT = U.S. Department of Transportation • FHWA = Federal Highway Administration • FMCSA = Federal Motor Carrier Safety Administration • GAO = U.S. Government Accountability Office • LCV = longer combination vehicle • MAP-21 = Moving Ahead for Progress in the 21st Century Act • NHS = National Highway System • OMB = Office of Management and Budget • PaveDAT = Pavement Damage Assessment Tool • TIFA = trucks involved in fatal accidents • UK = United Kingdom • VDOT = Virginia Department of Transportation • VMT = vehicle miles traveled • WIM = weigh-in-motion

Session C: General Discussion (Breakouts 1 & 2)

Table 4. General discussion (breakouts 1 & 2).
Topic Comments Next Steps
Operational Impacts
Impacts of heavier trucks on small businesses. The impacts of heavier trucks on small businesses was included as a transportation cost in the modal shift analysis.
Movement to small truck engines is a factor for hauling more weight Engine size to operate the alternative configurations was included in the impact assessment on fuel consumption and air quality in the modal shift area of the Study.
Safety
Correlation of experience with safety The Study analyzed experience and safety factors in the Crash/Safety assessment.
Bigger trucks are detrimental to safety The comparative safety implications of the six alternative configurations were included in Crash/Safety area.
Dynamic performance
Truck growth is dynamic and must be factored into the Study and not held constant The estimates of scenario traffic resulting from introduction of each of the alternative configurations was an important step included in the Study.
Network considerations
Study the impact of State and local roads carrying higher weight trucks The impact of heavier trucks on State and local roads was qualitatively addressed in the Study; quantitative assessments were not possible due to limited data availability.
Trucks use certain roads or corridors-not all roads-study those well used roads This was done in the Study.
Fleet Size Issues
Impacts of heavier weights on small truckers/owner operators: higher equipment costs, driving jobs, driver training, etc. Small truckers will not have leverage to set and collect higher rates to recoup higher costs and for more productivity for shippers. Issues listed are very specific and data was not available to conduct an adequate assessment of these aspects.
International Aspects
Comprehensive review of European methods to cover all aspects. European studies were included in the Desk Scan phase of the Study.
Foreign Competitiveness-higher weights to the ports The trucks assessed in the Study have implications in this area; a comparison of competitiveness by commodity is not within the scope of the Study.
Economic impacts/productivity & Environmental impacts
Shipper inefficiencies at ports, etc. affect trucking productivity. This comment is not within the scope of the Study.
Economic impacts-thoroughly address The economic impacts of changes to current Federal truck size and weight limits were addressed in the Study.
Include fuel usage for full as well as empty trucks. Both of these factors were included in the Study. Fuel use was assessed in the modal shift area of the Study while empty trucks were part of the truck weight data base used widely in the Study.
Larger trucks potential to reduce number of trucks and positively affect congestion This comment was assessed in the modal shift area of the Study.
Study the do-nothing option-has costs The Study focused on the MAP-21 requirement to identify and assess the impacts of various truck sizes and weight limits. The comment is not in the scope for the Study.
Deficiencies of deadheading larger trucks Deadheading alternative configurations was not assessed in the Study. The modal shift analysis would reflect empty trucks in the scenario traffic.
Review and address truck size and weight increases in the post-deregulation era. Trailers have increased several times: 45 ft. to 48 ft. to 53 ft. and 57 ft. (in selected States) Where prior studies have been completed in this area, they were included in the Desk Scans for the project.
Enforcement
Static scale dimensions may be inefficient for weighing larger/longer trucks, increase time. The time differential for weighing and inspecting the different configurations was included in the enforcement cost area of the compliance analysis of this Study. The need to replace weigh bridges currently in use was assessed with the assistance of CVSA.
Previous Studies
Industry and Government may submit study materials The Desk Scans provided opportunity to do this.
Control for bias to heavier trucks on contract team and in administration FHWA controlled for potential bias throughout the Study process.
Impacts on State laws
Study States that have larger configurations on Interstate by grandfather provision or State road provision The States of Idaho, Michigan, and Washington are examples of such States that were included in the Study.
State Option for truck configurations Analysis of State options was not in the scope of the Study.
Impacts on State laws
Driver Training effect on retention and safety by truck configurations An assessment of the effect of driving training is not in the scope of the Study.
Modal Shift
Commodities that will use larger trucks. The modal shift analysis identified and applied impacts to shipping choice for general commodity types caused by the introduction of alternative configurations.
Modal shift-LTL’s not affected The modal shift assessment reflected this input.
Key to freight haulage is intermodal and choice relates to rates for all modes The Modal Shift analysis included in this Study addressed the issue of rate adjustment for truck and rail modes.
Bridge Formula
Consider bridge formula in determinations The Study included an application of the bridge formula in the compliance section, as a factor in enforcement effectiveness.
CVSA = Commercial Vehicle Safety Alliance • FHWA = Federal Highway Administration • ft = Foot • LTL = Less than Truckload • MAP-21 = Moving Ahead for Progress in the 21st Century Act


Table 5. Webinar - vehicle configuration.
Topic Comments Next Steps (Safety Group)
Specific Configurations recommended
10-axle Rocky Mountain Double This configuration was considered but not included in the Study in light of alternative configurations of greater interest to stakeholders.
9-axle turnpike double at 120,000 lbs. This configuration was considered but not included in the Study in light of the alternative configurations of greater interest to stakeholders.
53 ft. turnpike doubles as used in Ontario pilot program This configuration was considered but not included in the Study in light of the alternative configurations of greater interest to stakeholders.
The 8 and 9-axle B-double is in wide use in Canada and elsewhere. Highly recommend it be one of the configurations studied. The 8-axle B-double with 33-37-foot trailer lengths, coupled with performance-based standards This configuration was considered but not included in the Study in light of the alternative configurations of greater interest to stakeholders.
4- or 5-axle truck cranes, dump trucks, other specialized hauling vehicles These vehicles are not in the scope of the Study. Congress required that a six-axle semitrailer and other tractor-semitrailer configurations be assessed.
Quad tractors and quad tankers for dairy industry – 120,000 lbs. This configuration was considered but not included in the Study in light of the alternative configurations of greater interest to stakeholders.
5-axle 88,000 lb. vehicles since many States have ag [agriculture] and forestry exemptions. This configuration was included in the Study.
5-axle at 88,000 would not require large investment in new equipment This configuration was included in the Study.
5-axle at 88,000 would result in 20 percent fewer trucks used to deliver to customers This configuration was included in the Study.
6-axle 107,000 lb. tankers widely used in New York. Study configurations used in some parts of country, but not in all parts. Two 6-axle trucks were included in the Study: 91,000 lb. 6-axle truck and 97,000 lb. 6-axle truck. A 107,000 six-axle truck was not included in the Study in light of the alternative configurations of greater interest to stakeholders.
It would be very efficient if one tractor could haul two 40 ft. containers into/out of ports on an appropriately designed configuration that was stable and maneuverable. This configuration was not included in the Study in light of the alternative configurations of greater interest to stakeholders.
The Study should consider heavier Canadian weight limits. The Volume I Summary Report discusses truck weight limits in Canada and Mexico.
28 ft. doubles, a current legal configuration, needs to be part of this Study. The stability, and thus safety, of this setup is much different from the 53 ft. singles. The 28 ft. double configuration was used as a control vehicle in the Study for comparative analysis purposes with the multiple trailer combinations that were assessed.
Needs of different industries
Consider what changes to configurations may result from the new port operations projected in response to the Panama Canal expansion. Check with MARAD before final decision on configurations. The Study included participation and input of MARAD staff on the POG. The alternative configurations studied reflected the input and interest of a wide range of stakeholders.
Lift axles, different axles spreads
These change the infrastructure impacts of vehicles. While axle positioning does change the impact of the vehicles, doing an extensive comparison of axle placement within a configuration was beyond the scope of the current Study.
Safety
LCVs do not always operate in perfect conditions, e.g. bad weather This is true for all vehicles. Furthermore, scientific literature in the Desk Scans indicated that special policies may be needed for LCV operations.
Braking
Longer, heavier (10/11 axle Rocky Mountain Doubles) have twice as many brakes for only 60 percent more weight. They corner and stop better than 80,000 lb. 5-axle trucks. Rocky Mountain Doubles were not included in the Study in light of the alternative configurations of greater interest to the stakeholders.
Would trucks need to be retrofitted to accommodate the need for stronger brakes? This is outside the scope of the Study.
88,000 lbs. on 6 axles would not increase stopping distance nor cause any additional road/bridge degradation. An 88,000 pound, six-axle configuration was not included in the Study in light of the alternative configurations of greater interest to stakeholders.
Network considerations
Interchange ramp clearance. This analysis was not conducted due to a lack of data.
Operations in mountainous terrain. Various terrain types were included in the assessment of the alternative configurations assessed in the Study.
Operations in urban areas. Large trucks have massive blind spots and require large road geometrics that in turn encourage fast driving by other vehicles. Both create hazards for pedestrians. Smaller, well-designed trucks are more appropriate for urban areas. Vehicle tracking was included in the vehicle stability and control area of the Crash/Safety area of the Study.
Parking and break-up issues for B-train configurations, other LCVs. Break-up issues were qualitatively assessed in the modal shift area of the Study. Changes in truck parking needs were not addressed due to limitations on adequate, available data.
Impacts on State networks. The Study primarily addressed impacts on NHS routes due to the availability of adequate data.
Need for staging areas when LCVs get to State roads. Staging areas or break-up/make-up lots were qualitatively addressed in the modal shift area of the Study.
Same degree of reasonable access likely will not be possible for longer vehicles. Data availability limitations inhibited an assessment of reasonable access routes unless those routes were on the NHS.
Port access and other last mile needs may not be feasible with LCVs. Some LCVs may not be able to travel directly to ports or other destinations.
Bridges
Total distance between axles should comply with the Federal Bridge Formula The Study was not limited to vehicles that comply with the bridge formula.
Allow States to increase gross weight on the Interstate system as long as it meets Federal Formula B The Study was not limited to vehicles that comply with the bridge formula.
The most important issue for States such as Washington with existing higher weight limits is the impact on bridges. We follow AASHTO bridge standards, and believe that higher weights proposed by some groups will damage bridges, regardless of axle configuration. The Study assessed the extent of damage and the cost in relative terms.
Pavements
10 axle Rocky Mountain doubles at 129,000 lbs. put less weight per axle group than 80,000/88,000 semis. Rocky Mountain Doubles were not included in the Study in light of the alternative configurations of greater interest to stakeholders.
Balance fuel efficiency with pavement damage. The assessments completed in the Study included both elements. Pavement was an area of analysis in the Study and fuel consumption implications were included in the modal shift area of the Study.
Test configurations with alternative axle loads to determine at where pavement impacts become unacceptable. The Study assessed the impact that the alternative configurations were estimated to have on pavements including an analysis of the full spectrum of axle weights observed in WIM data.
Performance-based standards
Consider configuration’s handling, stability characteristics as well as its low-speed off tracking This work was completed in the vehicle stability and control area included in the Crash/Safety analysis of the Study.
Focusing only on dimensions/lengths instead of focusing on the configuration’s operational performance characteristics limits design possibilities. The value of assessing the alternative configurations in the vehicle stability and control area of the Study was understood and completed.
Low speed off tracking performance assessment as it is now done assumes fixed trailer wheelbase lengths. If a performance standard approach was used, it is highly likely steerable axles could become prevalent while still enabling good maneuvering performance. This possibility should be considered. Assessments of vehicle stability and control did not include recommendations as to how to improve the tracking of the configurations; that was outside the purpose and scope of the Study.
Permit operations
Would certain vehicles operate only under special permit? Whether certain vehicles would operate under special permit in the future did not relate to the analysis. Legal permitted loads were included in the truck weight data set used in the Study.
AASHTO = American Association of State Highway and Transportation Officials • ft = feet • lb = pound • LCV = longer combination vehicle • MARAD = Maritime Administration • NHS = National Highway System • POG = Policy Oversight Group • WIM = weigh-in-motion

Table 6. Webinar - data, methods, and models.
Topic Comments Next Steps
Economic Impacts/ Productivity
A more productive trucking industry could lead to an increase in Gross Domestic Product (GDP). Macroeconomic modeling to estimate impact on GDP is beyond the scope of the Study.
Fewer trucks would be required to haul the same amount of freight. The modal shift analysis area of the Study estimated the changes in truck travel levels needed to haul a given amount of freight using all modes.
Do studies not show that when weight limits go up, number of trucks also increase, since per ton mile cost goes down? The Desk Scans did show that truck traffic has not decreased following size and weight increases, but did not indicate a link between this increase and changes to costs per ton-mile.
Separate study for non-divisible loads, i.e. bulk liquids/tankers. Vehicle dimensions do not change; simply add a 6th axle (tri-axle trailer) and increase productivity by almost 50 percent from 80k to 107k. The Study examined different alternative configurations including (in a limited way) various axle sets and configurations and the kinds of commodities carried by these configurations.
Safety
Societal costs of crashes should be included in the Study The Study analyzed changes in crashes and safety associated with operating each of the alternative configurations but did not specifically determine the broader societal cost of crashes. Lack of truck weight data inhibited the extent to which this consideration could be conducted.
ATRI recently completed study on large truck safety trends that should be considered. Previously completed studies by ATRI were considered in the Desk Scans for the Study.
The major limitation of TIFA is the lack of specificity with regard to the specific weight of the truck involved in the fatal accident. This was true for all data sources examined and evaluated for use in the Study. The lack of truck weight data linked to truck crashes was reported as a finding in the Crash/Safety area of the Study.
Will [the researchers] review and utilize the Dynamic Performance Indicator (DPI) method for determination of heavy truck safety? This model includes accident statistic data. Author/developer of the model is an Alfonso Corredor, PhD. Simulated data to consider rollover threshold, front and rear out-swings, off-tracking (low and high speed)? The same metrics used for the 2000 CTSW Study were used in the current Study. DPI requires crash rates for specific configurations. Since crash rates by configuration are generally not reported, the use of DPI was not feasible. Tracking was a key element assessed in the vehicle stability and control area of the Crash/Safety analysis.
When looking at historical crash data on oversize and heavier trucks, a researcher needs to look beyond the success stories and look at the additional driver training, screening and monitoring that exists behind the scenes. Generally, this was considered in the assessments completed in the Crash/Safety area of the Study.
Safety analysis: cannot simply extrapolate data from one State and apply nationally. What may be "safe" in Michigan may not be safe in a mountainous State or on high volume roadways. Findings from the truck crash assessments were not extended to the national level, partially for this reason.
FMCSA-sponsored "Cost- Benefit Analysis of Onboard Safety Systems," breaks out the real-world, line-item costs of crashes by truck type, severity, commodity-involvement An evaluation of on-board safety systems is outside of the scope of the Study.
It has been a long time since the last DOT sponsored "Technology Scan" of Europe and Scandinavia but both places have vast amounts of safety info and wisdom and folks who may well be willing to share it. Specific to truck size and weight (TSW), there has been much recent good work accomplished--hope you can include it in the American Study. Studies completed in Europe were included in the Desk Scan phase of the Study. Data used in the Study was limited to U.S.-relevant data since differences in a variety of factors relating to trucking in other countries limit the applicability of the data to this Study.
Data on Truck Configurations and Operating Weights
Consider using virtual weigh station data. This would be what is actually out there. The truck weight data sets reported to FHWA by the States was extensively used in the Study. To the extent that virtual weigh stations are a source for this reported data, it was used in the Study.
Any States that have done or are doing calibration for Mechanistic-Empirical Pavement Design Guidelines (MEPDG) implementation should have higher quality truck and truck damage data than States that have not done this calibration In selecting pavement sections to be assessed in the Study, Long Term Pavement Performance (LTPP) sites were used to the extent practicable, for this reason.
A State WIM network is probably the minimum requirement for providing competent data. Truck weight data reported to FHWA by the States was used extensively used in the Study.
WIM data not always reliable. Quality control procedures applied by the States and FHWA render the best available truck weight data currently available; this data was extensively used in the Study. Additional evaluation of the truck weight data was applied to ensure the use of quality data.
Environmental Impacts
Optimization of freight produces fewer grams of CO2/ton-mile. The modal shift analysis examined emissions resulting from the introduction of each alternative configuration.
Bridge Impacts
Must consider impacts of functionally obsolete bridges, not just the structural characteristics of the bridges. Look at the effect of heavier trucks on functionally obsolescent facilities. We studied impacts on the most common and representative bridge types in FHWA’s National Bridge Inventory (NBI). Functionally obsolete bridges were not included; bridge analysis focused on structural strength and the ability of the nation’s bridges to accommodate the configurations.
Truck weight limits are based on a 1950’s study when most bridges and tunnels were new; most bridges are at a satisfactory rating so should we not be looking at lowering the weight limits until the infrastructure is back to 100 percent? Load rating analysis reflected the current reported condition of all bridges; Study findings included the additional investment that would be required to accommodate the alternative configurations.
In SCDOT, we did fatigue analysis for four archetype bridges. The Study was included in the Desk Scan phase.
The number of sample bridges seems insufficient. Bridges selected for Study are representative of those located on the Interstate and NHS. The number of bridges included in the Study is affected by the availability of data needed to perform structural strength assessments using AASHTO’s BrR.
Not all States use Load Resistance Factor Rating. Determine fatigue of steel members and deck, salt induced decks and vibrations. Determine use of Posting, enforcement, re-evaluate bridge formula. Understand and use of practical rehabilitation and strengthening techniques to ensure level of uniform. Contact States and AASHTO 2010 posting analysis completed before Michigan. No deterioration models exist that determines quantifiable service life loss as weights increase. We used Load Factor Design where quality Load Resistance Factor Rating models in ABrR (VIRTIS) were not available.
Number of Bridges is too low. The sample should be based on the corresponding percentages of different types of structures on the Interstate. The sample was drawn in consideration of this and of bridge types located on the NHS. Data available through the NBI was used to determine the bridge types that were included in the Study.
The deterioration models from Bridge Management System consider time and service environment, but not load. Fatigue models consider load explicitly. For other impacts, more basic work is needed to relate bridge deterioration to truck weight. Load was an important factor assessed in the bridge analysis area of the Study.
Cluster data analysis on the various bridge structure types around the country. This technique was applied in the bridge analysis area of the Study.
Really should look at the process that National Cooperative Highway Research Program (NCHRP) 12-78 used to make a sample set of bridge models that was reflective of the real-life bridges found in the NBI. NCHRP 12-78 was identified in the Desk Scan phase of the Study.
Suggest you get both Boeing Aircraft engineering and ATI Wah Chang Corrosion analysis division in on the Study. The reason for and relevance of this comment is not given.
Idaho DOT did a bridge analysis in conjunction with an LCV pilot program. The studies completed by Idaho DOT and reported to the State Legislature were included in the Desk Scans.
Pavement Models
Joints can be examined via the load transfer efficiency, but current models may not address durability issues in concrete States collect pavement condition data. The AASHTOWare® Pavement ME Design model that was used is calibrated to empirical data.
SCDOT used DARWIN in its pavement deterioration project. AASHTOWare® Pavement ME Design is the latest pavement assessment and design model available and it was the primary tool used in the pavement assessment area of the Study.
In GA, we are going through M-EPDG calibration now. It is apparent that WIM is critical. Currently, we have indications that we have high levels of non-compliance with weight limits. "Non-compliant" trucks may be carrying a legally issued overweight hauling permit. Such vehicles were included in the Study to the extent that they are present in the truck weight data set supplied by FHWA.
Operational Impacts
Impacts of heavy trucks that are not able to maintain speed in mountainous terrain Operational considerations, including operations in various terrain settings, were assessed in the modal shift analysis.
Congestion in highway system or railway could be an issue. Impacts on congestion levels were assessed in the modal shift analysis area of the Study.
Independent from injuries and fatalities, major highway shutdowns and closures seem to be from twin and triple trailers, but I have no data for this. Agreed that LCV crashes may take longer to clear, but we were not able to evaluate the full extent of this impact due to data availability limitations.
Acceleration data is needed since heavier trucks with same horsepower, torque, and gear ration will take longer to accelerate, which can affect signal timing, work zone stoppages, on-off ramps and safety when mixing in with cars. Truck engine performance was evaluated for each of the alternative configurations included in the Study as part of the analysis completed in the modal shift area of the Study.
Dynamic Performance
Consider full dynamic performance analysis. Safety analysis must not only include accident statistics but also real world simulation techniques such as low-speed off-tracking, high-speed off-tracking, transient off-tracking, etc.. Compare wide based single tires with dual tire set-up. Tire type comparisons and evaluations are outside the purpose and scope of the Study. The vehicle stability and control area assessed vehicle tracking. Results in this area are included in the Crash/Safety technical report.
If increased weights mean higher loads, we will have even more rollovers. Talking about axles and brakes neglects this issue. Simulation and safety analysis sensitive to changes in the vehicle’s center of gravity was completed as part of the vehicle stability and control assessment included in the Crash/Safety area of the Study.
Modal diversion
Consider the amount of freight tonnage that will be diverted from rail to highway due to the various configurations, and thus the acceleration in roadway deterioration Outputs that measured the effect of introducing each of the alternative configurations on shifts between modes were completed in the modal shift analysis area of the Study.
Take into account differing freight trends for each State. State trends were not separately derived in the Study; rather, they were based on modal shift impacts assessed on a corridor basis. Results were reported on a national basis.
Identify commodities that are candidates for modal shift. At the margin, there are commodities that are more likely to shift than others. Also, distance and time are important characteristics for modal shift. This approach was followed in the modal shift analysis area of the Study. It was understood that certain commodities are more susceptible to rail-to-truck shifts and this consideration was applied in the Study.
Financial impacts on short-line railroads are important. Impacts on regional and short-line railroads were assessed in the Study. An enhanced capability to evaluate regional and short-line rail shifts is included as a recommendation of the Study.
If you focus on commodities within a BEA - BEA level comparison may get around county details. You should also use this to get a base modal share within regional corridors. The modal shift analysis area of the Study was conducted at the county level in order to get the finest level of Origin/Destination data to provide the best estimate of modal shifts among different vehicle configurations
Need to consider the capacity of other modes to handle modal shift. This was considered as part of the modal shift analysis area of the Study.
Many private sector companies likely have modal diversion models and related data. In stakeholder input events, we requested information on such models but none were offered for use in the Study.
Consider impacts associated with larger vessels using Panama Canal, especially for southern ports This was considered in the modal shift area of the Study to the extent that it is reflected in existing freight forecasts.
AASHTO = American Association of State Highway and Transportation Officials • ATRI = American Transportation Research Institute • BEA = Bureau of Economic Analysis • BrR = Bridge Rating • CO2 = Carbon Dioxide • CTSW = 2000 Comprehensive Truck Size and Weight Study • DOT = U.S. Department of Transportation • DPI = Dynamic Performance Indicator • FHWA = Federal Highway Administration • FMCSA = Federal Motor Carrier Safety Administration • GDP = Gross Domestic Product • LCV = Longer Combination Vehicle • LTPP = Long Term Pavement Performance • MEPDG = Mechanistic-Empirical Pavement Design Guidelines • M-EPDG = Mechanistic Empirical Pavement Design Guide • NBI = National Bridge Inventory • NCHRP = National Cooperative Highway Research Program • NHS = National Highway System • SCDOT = South Carolina Department of Transportation • TIFA = Trucks Involved in Fatal Accidents • TSW = truck size and weight • WIM = Weigh-in-Motion


Table 7. Webinar - general comments.
Topic Comments Next Steps
Driver Education
Driver education will be important This point is qualitatively addressed in the Crash/Safety area of the Study.
Driver Certification
LCV operators should be certified This point is qualitatively discussed in the Crash/Safety area of the Study.
Previous studies
How will the Study address previous studies, like the Vermont Study? The Vermont Study was included in the Desk Scan area of the Study.
Reviewing findings of previous studies may help in assessing the vehicles to examine in this Study. The Desk Scan phase of the Study was designed in part to accomplish this.
Western Governors Association (WGA) study included many aspects of what will be covered in the current Study. The WGA study was included in the Desk Scan phase of the CTSWL Study.
Parking
Parking and truck rest areas not designed for LCVs. Parking facilities were not extensively assessed in the Study due to data availability limitations. This issue was qualitatively discussed in the Study.
Weigh stations
Most State scale facilities are not designed to weigh combination vehicles. The Compliance and Enforcement area of the Study addressed this with input from the CVSA.
Operating environment
LCVs do not always operate under perfect conditions. Consider operations in inclement weather, in mountainous terrain, in dense urban areas. The operation of the alternative configurations operating in a variety of terrain types was completed in the modal shift analysis area of the Study.
Number of drivers
Fewer, more experienced drivers required if LCVs allowed. Fewer drivers is not a benefit. LCV driver qualifications were not specifically analyzed but a discussion on qualifications is included in the Crash/Safety area of the Study.
Highway design standards
Longer, heavier vehicles could create need to modify highway design standards The findings from the vehicle stability and control analysis area of the Crash/Safety analysis are useful in considering this need.
New truck configurations would require new load ratings for bridges. The bridge analysis area of the Study assessed the structural strength state of the bridges included in the Study; results of this analysis can be used to evaluate this need.
Should include an impact study on cable barriers of trucks over 80k; could also recommend no trucks over 80k allowed in left lane to keep them away from the median cable barriers. The issue of cable barriers was considered in the Study but could not be rigorously examined due to current limitations in the evaluation tools. A recommendation to enhance these tools is presented as a recommendation in the Study.
Would need collision force criteria for bridge rail and piers. Collision force criteria is an aspect of barrier and guard rail assessment modeling capabilities that need upgrading, as discussed above.
What would be the impact on the majority of the Interstate designed to old geometric requirements? (particularly interchanges) See the vehicle stability and control area of the Crash/Safety analysis.
Bridge Formula
Would need a new bridge formula since 6-axle 97,000 tractor semitrailer does not comply with current bridge formula. The issue that seems to get pushed aside all too often...the Federal Bridge Formula is the prevailing standard...how will it be factored into this Study? Is it obsolete? Does it need to be amended? Either use it or get rid of it. An evaluation of the Federal bridge Formula-B was not within the scope of this Study. The bridge formula was relevant to the compliance analysis area of the Study.
Enforcement
Bridge limits would need to be posted, enforced heavily, and made available for use in truck-specific GPS units. Implications that each of the alternative configurations have on bridge postings was addressed in the bridge analysis area of the Study.
Consider on-board weighing technology Evaluation of on-board weighing technology was outside the scope of the Study.
The Study needs to evaluate and acknowledge current issues with existing trucks exceeding weight limits, in particular on local bridges, and lack of enforcement. Violations are an everyday occurrence with economic impact to counties. How might this be increased with heavier trucks? The truck weight data set included trucks of this type and was included in the assessments completed in the bridge analysis area of the Study.
Viable size and weight enforcement provision is inextricably linked to this Study. The Study assessed the impacts on the delivery of effective enforcement generated through the operation of each of the alternative configurations.
Truck maintenance costs
Maintenance costs increase as truck weights increase. Assessing vehicle maintenance needs is outside the scope of the Study.
More frequent inspections of truck frames, floors, and other load-bearing components. Specific truck inspection actions were generally considered in the violation and citation area of the Crash/Safety analysis completed in the Study. Element-specific inspection assessments are outside the scope of the Study.
Consistency with other agencies’ regulations
Consider impacts of performance on related rules such as Environmental Protection Agency (EPA)/NHTSA greenhouse gas and EPA SmartWay and State rules. An evaluation of the elements included in EPA’s SmartWay Program is beyond scope of the Study. The Study’s fuel consumption analysis and air quality impacts, including greenhouse gas emissions, were included in the modal shift analysis area of the Study.
Obsolescence of older equipment
Apparent concern about existing equipment becoming obsolete and need for trucking companies to purchase new equipment. The Study did not include an analysis of equipment obsolescence; rather, it assessed the impacts of each alternative configuration in areas outlined in the law.
Productivity
Cannot make current vehicle less competitive. The modal shift analysis assesses the truck-to-truck shifts in load movements, including consideration of the impacts on the baseline vehicle, as part of the modal shift analysis.
Separate passenger and freight traffic
The best possible thing we could do is to build a separate, parallel Interstate highway system and separate cars and trucks. Would be great for everyone. The Study did not include an assessment of the need for a duplicate, parallel Interstate System.
Truck/bike interaction
Bike use is growing and actively encouraged in cities. Bikes and trucks are operating in shared space. Will bike/truck safety be a priority in the Study? Also, can FHWA prepare expanded safety promotional materials to educate bikers and truckers about better safety practices, including blind spots, low profile recumbent bikes, wide turns, and loose equipment? Consideration of the impacts on bicycle/truck safety was not within the scope of the Study. The recommendation for expanded safety materials is noted and has been shared with the relevant program offices.
Permit fees
Overweight permit fees do not typically cover cost of additional infrastructure damage. The adequacy of permitting fees and charges required by the States was not addressed in this Study.
ITS can improve safety
Tomorrow’s Intelligent Transportation Systems (most especially ITS safety systems) can change enhance yesterday's constraints re: truck size and weight issues and prospects. Suggest paying careful attention to 5.9 GHz technologies. An assessment of Connected Vehicle Program benefits was outside the scope of the Study.
Impacts on State laws
Should also include an inventory of all State laws that would be affected by a change in Federal truck size and/or weight limits. A separate provision of MAP-21, Section 32802, called for a compilation of State truck size and weight laws. This additional report was conducted separately from this Study and was released in the fall of 2015.
CTSWL = comprehensive truck size and weight limits • CVSA = Commercial Vehicle Safety Alliance • EPA = Environmental Protection Agency • FHWA = Federal Highway Administration • ITS = intelligent transportation systems • LCV = longer combination vehicle • MAP 21 = Moving Ahead for Progress in the 21st Century Act • NHTSA = National Highway Traffic Safety Administration • WGA = Western Governors Association

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