Comprehensive Truck Size and Weight Limits Study - Volume 1: Technical Reports Summary

Executive Summary

This summary describes the approach and presents the technical results of the U.S. Department of Transportation’s (USDOT) Comprehensive Truck Size and Weight Limits Study (CTSWL Study or "the study") required by Section 32801 of the Moving Ahead for Progress in the 21st Century Act (MAP-21) (P.L. 112-141).

The statute directed the Secretary of Transportation, in consultation with States and appropriate Federal agencies, to conduct a comparative analysis of the impacts from trucks operating at or within current Federal size and weight regulations to trucks operating above those limits. The legislation also specified that the analysis include six-axle tractor-trailers and other alternative configurations. In response to the congressional direction, the study analyzes:

• Highway safety and truck crash rates, vehicle performance (stability and control), and inspection and violation patterns;
• Pavement service life;
• Highway bridge performance; and
• Truck size and weight enforcement programs.

FHWA did not intend to develop or support a position on changes to current Federal truck size and weight limits in this study; rather, the agency intended to assess the impacts that any such changes might have in the various areas included in the study to better understand the impacts that trucks operating above current Federal truck size and weight limits have today. The study was set up to provide the results of the assessments that were completed and to provide a summary of this analysis to Congress.

A key required step in the analysis was to estimate the effects that changes in current Federal truck size and weight limits could be projected to have on the movement of freight by truck type, by roadway type, and by freight transportation mode. The projected shifts in goods movement among truck types and between modes generated estimates of travel demand changes and affected the magnitude of potential impacts in the areas of highway safety, vehicle performance, and violation patterns; pavement and bridge performance; and in the delivery of effective truck enforcement programs in each of the scenarios. Estimated changes in truck travel demand also provided the basis for analyzing projected fuel consumption, air quality, and traffic and modal operations.

The last comprehensive study of this type was completed by the Federal Highway Administration (FHWA) in 2000. That was followed by the Western Uniformity Scenario Analysis, which was published for the Western Governors’ Association by FHWA in 2004 and focused on the impacts of expanding Longer Combination Vehicle (LCV) operations in the Western States. Since then, other agencies and organizations have looked at various aspects of truck size and weight regulations in individual States or regions and at freight transportation issues in general. These reports present a range of findings that address changes in truck size and weight regulations and the impacts of those changes on industry productivity, infrastructure, safety, and the environment. To understand these diverse views, FHWA conducted extensive outreach and a thorough literature search of prior research at the outset of this study.

This study builds off of the body of previously completed work, introducing improved models and data sets. Nevertheless, significant limitations in data availability persist, which also affected prior studies. For example, the lack of descriptive information regarding commercial motor vehicles involved in crashes continues to prevent adequate analysis of highway safety and truck crashes. The lack of data on gross vehicle weight (GVW), number of axles on a vehicle, and the spacing between the axles imposed significant constraints in drawing national-level conclusions. In addition, the lack of crash data relevant to oversize trucks impeded the study team’s ability to project crash rates of different truck sizes and configurations on a national scale.

Section 32801 also required an assessment of the impacts that a six-axle and other alternative tractor-trailer combinations would have if they were allowed to operate throughout the Nation. Accordingly, the USDOT selected six alternative truck configurations to examine, each the subject of a separate scenario analysis with a related control vehicle that meets current Federal size and weight standards. The six different scenarios were developed to see what the likely results would be if an alternative truck configuration were allowed to operate on a specified highway network in comparison to a control vehicle. In general, the scenarios’ alternative truck configuration uses the nationwide network and access rules of the control—with the exception of the triple truck configuration, which has a restricted network and access rules. Table ES-1 shows the vehicles that were considered under each scenario as well as the existing configuration from which the most traffic would likely shift.

The balance of this executive summary presents the high level study process and results.

About the Study Process

The study process included: 1) analysis in five separate focus areas, 2) extensive stakeholder and public input, 3) peer reviews by the National Academies of Science, and 4) website publication of all focus area project plans and desk scans. Furthermore:

• Section 32801 of MAP-21 established the requirement for the study;
• Congress specified the technical areas of focus;
• USDOT chose the alternative truck configurations and scenarios, incorporating stakeholder input;
• The study team conducted a Desk Scan (literature searches) of previous work on truck size and weight issues;
• The study team proposed data and models for the analysis;
• Detailed project plans were prepared for each focus area, identifying approaches to analyze the impacts on safety, pavement, bridge and enforcement and on modal diversion;
• USDOT-led teams conducted the analysis; and,
• Technical reports were prepared for each of the five focus areas.

The key findings, assumptions and limitations by focus area are summarized below.

Table ES-1: Truck Configurations and Weights Scenarios Analyzed in the 2014 CTSWL Study

Scenario	Configuration	Depiction of Vehicle	# Trailers or Semi-trailers	# Axles	Gross Vehicle Weight (pounds)	Roadway Networks
Control Single	5-axle vehicle tractor,53 foot semitrailer (3-S2)		1	5	80,000	STAA 1 vehicle; has broad mobility rights on entire Interstate System and National Net­work including a significant portion of the NHS
1	5-axle vehicle tractor, 53 foot semitrailer (3-S2)		1	5	88,000	Same as Above
2	6-axle vehicle tractor, 53 foot semitrailer (3-S3)		1	6	91,000	Same as Above
3	6-axle vehicle tractor, 53 foot semitrailer (3-S3)		1	6	97,000	Same as Above
Control Double	Tractor plus two 28 or 28 ½ foot trailers (2-S1-2)		2	5	80,000 maximum allowable weight 71,700 actual weight used for analysis 2	Same as Above
4	Tractor plus twin 33 foot trailers (2-S1-2)		2	5	80,000	Same as Above
5	Tractor plus three 28 or 28 ½ foot trailers (2-S1-2-2)		3	7	105,500	74,500 mile roadway system made up of the Interstate System, approved routes in 17 western states allowing triples under ISTEA Freeze and certain four-lane PAS roads on east coast 3
6	Tractor plus three 28 or 28 ½ foot trailers (3-S2-2-2)		3	9	129,000	Same as Scenario 5 3

Modal Shift

The modal shift analysis provides the foundation for assessing a range of potential impacts associated with the truck size and weight scenarios analyzed in this study. “Modal shift” refers to shifts in freight usage between truck and rail modes as well as across vehicle types and operating weights within the truck mode.

• The FHWA is projecting a 45 percent growth in freight tonnage by 2040 that will generate an increase in demand for capacity to move freight, regardless of any changes in truck size and weight limits. However, for study purposes, the amount of freight to be moved was held constant at 2011 levels. If growth in freight were considered, the VMT reductions calculated by the model would be offset in 1 year by the forecasted growth due to freight demand. In light of this, the following results should be considered for their effects relative to other scenarios, but they are not predictive of real, long-term effects on truck VMT.
• Several data limitations were encountered including:
  1. Lack of precise origins and destinations of shipments,
  2. Unknown routes used to ship commodities,
  3. Limited WIM data availability off the Interstate System, and
  4. A model that does not account for state weight exemptions for truck hauls of certain commodities in bulk to rail or water head.
  USDOT does not believe that these limitations affect overall study conclusions, but the limitations must be kept in mind when considering study implications.
• The vehicle miles traveled (VMT) needed to haul the volume of freight estimated in the 2011 Freight Analysis Framework declined under all six scenarios relative to the control or base case VMT. As would be expected, changes in VMT mostly varied by the gross vehicle weight allowed in each scenario.
• Total logistics costs for transporting freight declined for all scenarios relative to the control situation, with greater declines estimated for Scenarios 1 through 3. This reflects higher transportation costs for shipping bulk commodities in the more lightly loaded control vehicle.
• The modal shift analysis assessed shifts between the truck and rail modes, as well as shifts in vehicles and operating weights within the truck mode. The amount of freight that shifted from existing truck types to the other truck scenario types was significantly higher than shifts estimated from rail to truck for each of the scenarios modeled. The greatest projected level of truck-to-truck shifts occurred in Scenarios 1, 2 and 3.
• Truck and rail modes are partners in some transportation markets, but are competitors in other markets. Although diversions from rail to alternative configuration trucks were seen under all six scenarios, these diversions were much greater for the five-axle, 88,000-lb. configuration in Scenario 1, the six-axle, 91,000-lb. configuration used in Scenario 2 and the six-axle, 97,000-lb. configuration used in Scenario 3. Scenario 3 produced the largest impact on rail share of freight with approximately $562 million in rail shipments shifting to the six-axle 97,000-lb. truck configuration trucks.
• Special attention was applied to assessing the impacts that the scenarios could have on regional (Class II) and short line (Class III) railroads. Estimates of the impacts on regional and short line railroads were completed using data reported on the Surface Transportation Board’s Carload Waybill Sample. The commodities hauled by short lines are moved in quantities that would only be affected by the truck size and weight changes in Scenarios 1, 2, and 3. Using the same general methods as were used to analyze rail impacts for Class I railroads, short line railroads were estimated to lose between one and four percent of total revenue under each of Scenarios 1, 2, and 3. Revenue losses under Scenario 3 would be somewhat greater than losses under Scenarios 1 and 2. Losses for some individual short line railroads could be greater. Although the analysis identified waybills that would be diverted under Scenarios 4, 5 and 6, the results were not included in the analysis due to significant data constraints with reported revenue.
• As a result of reduced truck VMT, road congestion-related costs would decline, with cost savings ranging from $256 million in Scenario 1 to $875 million in Scenario 4. All truck configurations used in the six scenarios would result in a decline in fuel costs; carbon dioxide emissions, the most prevalent greenhouse gas; and emissions of nitrogen oxide, an air pollutant, when compared to the control situation.

Safety

The safety comparative analysis explores the differences in safety risk and truck crash frequency between truck configurations currently operating on the Nation’s roadways at and below current Federal limits to those operating above such limits. The safety analysis also compares crash frequency and severity associated with base-line control vehicles with the six alternative truck configurations. To accomplish these purposes, three different analytical approaches were pursued: 1) crash-based analyses; 2) vehicle stability and control analyses; and, 3) safety inspection and violations data analyses.

• It is not possible to draw national conclusions or present findings concerning national crash rates due to a lack of relevant crash data. In many cases, crash data are drawn from a very limited sample of one or two States due to the actual range of operation of some of the truck configurations and problems with the quality of the data.
• Safety analysis results were, in part and to the extent possible, based on crash data from actual operations on U.S. roads. Weight data was not present in State truck crash reports, so an axle-based comparative analysis was completed. This analysis included data from those States that allow truck weights at or close to the alternative configuration weights as a proxy data set for weight.
• Crash rates for the six-axle alternative truck configuration in Washington State are significantly higher than the five-axle control truck rates. However, it is not possible to draw national conclusions or present findings concerning national crash rates due to a lack of comparable crash data in other States.
• The study did not analyze five-axle, 88,000-lb. trucks in Scenario 1 and 33-ft., twin-trailer combinations in Scenario 4. The five-axle, 88,000-lb. trucks could not be separately identified in State truck crash data reports due to the lack of weight information. In addition, the twin 33-ft. trailer combination is not in current use in the U.S. (other than in limited application on one route in one State), so no crash data was available.
• For analysis of maneuvering capability, the six-axle combinations used in Scenarios 2 and 3 did not differ appreciably from the five-axle semitrailer (maneuvering includes low- and high-speed off-tracking, stopping distance, and avoidance). Both the triple- and twin-trailer combinations used in Scenarios 4, 5, and 6 were most challenged by the avoidance maneuver. The “amplification” response of the third trailer in Scenarios 5 and 6 was greater than that of the second trailer in the control vehicle.
• The weight or size of a truck was not a strong predictor of the probability of driver and vehicle inspection violations (which included all driver and vehicle violations excluding over-weight violations). Other factors like driver age, vehicle age, and company “out-of-service” records were identified as stronger predictors of the probability of a violation. Note that the violations analysis excluded vehicles with over-weight violations to be consistent with the crash comparisons and the effort to compare legally operating vehicles in excess of 80,000 lbs. This analysis of violation data showed that trucks operating at or below current Federal weight limits had 2.8 to 3.5 violations per inspection, whereas trucks operating legally above those limits had 6.3 to 7.6 violations per inspection.

Pavement

The purpose of the pavement analysis is to address two major questions: how will changes in axle weights and types resulting from each scenario affect pavement performance and expected pavement costs, and how much pavement damage is currently caused by trucks operating above the current Federal weight limit versus trucks operating at or below those limits?

• For the pavement analysis, the study considered only Interstate and National Highway System (NHS) roads.
• The estimated impacts of the truck size and weight scenarios vary among both the scenarios and the pavement type and service conditions considered in the analysis.
• For the purposes of this study, life-cycle-cost (LCC) is defined as the agency cost for pavement rehabilitation (e.g., overlays, retexturing) over a 50-year analysis period. User costs, while important, were not considered in order to avoid complicating the analysis with the assumptions required for the estimation of user costs. Two interest rates were used in estimating the LCC for the pavement sections analyzed: a conservative rate of 1.9 percent was used, and a higher rate of 7.0 percent was used. As a result, the LCC estimates are reported as ranges.
• On average, the twin 33-ft. trailer combination used in Scenario 4 resulted in the largest overall LCC with an increase of 1.8 to 2.7 percent from the base scenario.
• The six-axle, 91,000-lb. configuration used in Scenario 2 resulted in a 2.4 to 4.2 percent decrease in predicted Life Cycle Costs (LCC) from the base scenario. This configuration features an additional axle with a weight increase of 11,000 lbs. compared to the five-axle, 80,000-lb. combination used as the base in the comparison. The six-axle, 97,000-lb. configuration used in Scenario 3 resulted in a 2.6 to 4.1 percent decrease in predicted LCC from the base scenario.
• The five-axle, 88,000-lb. configuration used in Scenario 1 and both triple trailer combinations used in Scenarios 5 and 6 showed small increases in LCC due to the higher axle weights as compared with the control vehicles.

Bridge

The bridge technical analysis work is focused on two main analytical objectives: a structural analysis and a bridge damage cost allocation.

The bridge structural analysis was designed to determine and assess the implications of the structural demand on U.S. bridges due to the introduction of the proposed alternative truck configurations.

The bridge damage cost allocation was designed to determine the increase or decrease in bridge damage-related costs expected to accrue over time due to the introduction of the proposed alternative truck configurations as compared with the costs attributable to the current truck fleet. For these analyses:

• The impacts of each scenario truck were assessed independently. The total number of bridges included in the sample that was assessed on the NHS, including the Interstate System, is 490 comprising 153 Interstate System bridges and 337 non-Interstate NHS bridges.
• It was not possible to draw national conclusions or present findings concerning the effect on overall bridge service life. While it is highly likely that bridge deck deterioration will accelerate with additional or heavier axle loads, the complex relationship of parameters that determine that performance is not well-defined.
• The introduction of the Scenario 2, 3, and 6 trucks affected the greatest number of bridges with posting (i.e., the need for strengthening or replacing a bridge) issues. The Scenario 3 truck configuration is projected to result in 6,215 bridges that would require strengthening or replacement, or 4.6 percent of Interstate bridges and 9.5 percent of other NHS bridges. The introduction of the Scenario 2 and 6 trucks is expected to produce 4,845 and 5,425 bridges with posting issues, respectively.
• Costs were estimated for bridge strengthening and replacement using project cost information from FHWA’s Financial Management Information System (FMIS). A unit cost for this type of work was calculated ($235.00 per square foot of deck space), applied to bridges requiring strengthening or replacement and summarized for each scenario modelled. Bridges requiring improvement action on the Interstate System (IS) and National Highway System (NHS) were flagged for improvement when a rating factor equal to or less than 1.0 was observed. Costs by span length for IS and NHS bridges are found in Table 23 of the Bridge Structure Comparative Analysis Report.
• The upper bound for projected one-time strengthening or replacement costs resulting from the introduction of alternative vehicles ranges from approximately $400 million for Scenario 1 to approximately $5.4 billion for Scenario 6.
• Relatively heavier axle loads and axle groupings tend to affect bridge fatigue life negatively when compared to the existing truck fleet. For the steel bridge analysis, the following ranges represent the incremental (per truck pass) effects on remaining fatigue life for each scenario truck as compared to the corresponding control vehicle:
  1. Scenario 1 – 25 to 27 percent greater incremental effect on fatigue life,
  2. Scenario 2 – 29 to 41 percent greater effect,
  3. Scenario 3 – 42 to 54 percent greater effect,
  4. Scenario 4 – 10 percent less to 17 percent greater effect,
  5. Scenario 5 – 29 percent less to 31 percent greater effect, and
  6. Scenario 6 – 54 to 64 percent greater effect.
  The overall effect on bridge fatigue life depends on the number of relatively heavier trucks that are in the traffic stream and the truck and axle weights.

Compliance

This area of the study assesses the cost and effectiveness of enforcing truck size and weight (TSW) limits for trucks currently operating at or below current Federal truck weight limits as compared with a set of alternative truck configurations in six scenarios.

• States spent approximately $635 million on truck size and weight enforcement in 2011. Personnel costs accounted for 85 percent of the spending, while facilities (including technology investments) accounted for the remainder.
• In all six scenarios, personnel costs for enforcement showed a slight decrease of approximately 1 percent or less relative to the base-case personnel costs, reflecting a reduction in truck vehicle VMT projected by the compliance analysis. This is not viewed as a significant finding. It should be noted that the reduction in personnel costs does not necessarily translate into lowering the level of enforcement; rather, it should be interpreted to mean that enforcement officials are able to weigh more trucks per truck mile of travel or shift investments toward emerging technologies. Either strategy adds effectiveness to enforcement programs.
• Comparisons of 13 States that use the 80,000-lb. weight limit as the beginning point for overweight enforcement to 16 States that allow higher weights under grandfather clauses showed little difference in enforcement costs relative to truck VMT in the State or in program effectiveness using the relationship between citation rate and enforcement intensity as the measure.

Table ES-2 summarizes the technical results of the study for each of the five focus areas: 1) modal shift, 2) safety, 3) pavement, 4) bridge, and 5) compliance. Following the table is a compilation of study highlights from each of the technical reports.

Table ES-2a. Study Results: Scenario Configuration Compared to Control Vehicle 1; Heavier Single Semi-Trailer Trucks

Scenarios	Modal Shift		Safety			Bridge Projected One Time Costs	Pavement Changes in Life-Cycle Cost	Enforcement Program Costs and Effectiveness
	Truck VMT	Total Logistics Costs	Crash	Vehicle Stability and Control	Violations and Citations
Five-axle truck @ 88k pounds	-0.6%	-1.4%	No national data or results; no analysis completed.	- Longer stopping distances - No difference in vehicle path or tracking	-Overall slightly higher violation rate and slightly lower out-of-service and citation rates -Configurations operating over 80k pounds had 18% more brake violations and a higher number of brake violations per inspection -Vehicle weight or configuration not predominant factors in predicting a violation	$.4 B	+0.4% to +0.7%	-0.3%; Positive (185,000 more trucks could be weighed for the same cost)
Six-axle truck @ 91k pounds	-1%	-1.4%	No national data or results; significant crash rate increase (+47%) in the one State (WA) analyzed.	6-axle heavy truck configurations did not differ significantly from the control vehicle in any of the maneuvers.	-Overall slightly higher violation, out-of-service and citation rates -Configurations operating over 80k pounds had 18% more brake violations and a higher number of brake violations per inspection -Vehicle weight or configuration not predominant factors in predicting a violation	$1.1 B	-2.4% to -4.2%	-0.4%; Positive (266,000 more trucks could be weighed for the same cost)
Six-axle truck @ 97k pounds	-2%	-3.2%	No national data or results; significant crash rate increases in the two States (ID +99%, MI +400%) analyzed.	6-axle heavy truck configurations did not differ significantly from the control vehicle in any of the maneuvers.	-Overall slightly higher violation, out-of-service and citation rates -Configurations operating over 80k pounds had 18% more brake violations and a higher number of brake violations per inspection -Vehicle weight or configuration not predominant factors in predicting a violation	$2.2 B	-2.6% to -4.1%	-1.0%; Positive (625,000 more trucks could be weighed for the same cost)

Table ES-2b. Study Results: Scenario Configuration Compared to Control Vehicle Longer Combination Trucks

Scenarios	Modal Shift		Safety			Bridge Projected One Time Costs	Pavement Changes in Life-Cycle Cost	Enforcement Program Costs and Effective-ness
	Truck VMT	Total Logistics Costs	Crash	Vehicle Stability and Control	Violations and Citations
Twin 33’ trailers @ 80k pounds	-2.2%	-6.3%	N/A [Configuration not in common use]	-Did not perform as well as the control vehicle in avoidance maneuver -Slightly longer stopping distance -Path deviation not affected by the ABS malfunction	-Twin trailers generally have higher vehicle inspection violation rates than five-axle 80k pound single trailers	$1.1 B	+1.8% to +2.7%	-1.1%; Positive (653,000 more trucks could be weighed for the same cost)
Triple 28’ trailers @ 105.5k pounds	-1.4%	-5.1%	No national data or results; Decrease in crash rate (-42%) in one State (ID) analyzed.	- Did not perform as well as the control vehicle in avoidance maneuver -Amplification of the third trailer’s response was greater than in the control -Some performance differences between the triples and twins in terms of braking or in the ABS malfunction -Off-tracking was greater than the control	-Sample size too small to conduct analysis	$0.7 B	+0.1% to 0.2%	-0.7%; Positive (452,000 more trucks could be weighed for the same cost)
Triple 28’ trailers @ 129k pounds	-1.4%	-5.3%	No national data or results; Minimal decrease in crash rate (-1%) on one roadway (KS Turnpike) analyzed.	- Did not perform as well as the control vehicle in avoidance maneuver -Amplification of the third trailer’s response was greater than in the control -Some performance differences between the triples and twins in terms of braking or in the ABS malfunction -Off-tracking was greater than the control	-Sample size too small to conduct analysis	$5.4 B	+0.1% to +0.2%	-0.7%; Positive (446,000 more trucks could be weighed for the same cost)

Table ES-3 provides a reference guide to Section 32801 requirements, FHWA responses to the legislative provisions, and where to find the study results in both the Volume 1 summary report and in the Volume II technical reports. The table is organized by Section 32801 subsections:

• Subsection (a)(1) to (a)(4): Provisions Related to Vehicles Currently Operating Above and Below Federal Truck Size and Weight (TSW) Limits
• Subsections (a)(5) to (a)(6): Provisions related to Alternative Configurations: Compare and contrast the potential safety and infrastructure impacts of current Federal TSW law and regulations;
• Subsection (a)(6) A to D: Under the assumption the Alternative Configuration is allowed, estimate extent to which freight would likely be diverted to other surface modes and to principal arterial routes and NHS intermodal connectors; and the effects of the diversion on public safety, infrastructure, cost responsibilities, fuel efficiency, freight transportation costs, and the environment; effect on the transportation network; and increases/decreases in total number of trucks on principal arterials and NHS connectors.
• Subsection (a)(7): Identify all Federal rules and regulations impacted by changes in truck size and weight limits.

Table ES-3. How/Where Study Addressed MAP-21, Sect. 32801 Requirements

Subsection (a)(1) to (a)(4): Provisions Related to Vehicles Currently Operating Above and Below Federal Truck Size and Weight (TSW) Limits with regard to:
Legislative Requirement	How Addressed	Where Addressed
Subsection (a)(1) Accident frequency	Crash-based analyses, using data from States and limited data from fleets.	Highlights: Volume 1. Technical Reports Summary, Chapter 3.2 (Safety Analysis) Technical report: Highway Safety and Truck Crash Comparative Analysis
Subsection (a)(1) Factors Relating to Accident Risk	Desk scan; analysis of vehicle stability and control, and analysis of safety inspection and violations data.	Highlights: Volume 1. Technical Reports Summary, Chapter 3.2 (Safety Analysis)
Subsection (a)(2) Impacts on Infrastructure (See also Bridge Impacts below)	Seven-step process employing latest pavement models, with existing databases to ascertain pavement impacts on specific sample pavement sections.	Highlights: Volume 1. Technical Reports Summary, Chapter 3.3 (Pavement Analysis) Technical report: Pavement Comparative Analysis
Subsection (a)(2) Costs and Benefits of infrastructure Impacts (in dollars)	Identification of life-cycle costs related to highway agency costs for pavement rehabilitation.	Highlights: Volume 1. Technical Reports Summary, Chapter 3.3 (Pavement Analysis) Technical report: Pavement Comparative Analysis
Subsection (a)(2) Percentage of Trucks Operating in Excess of Federal size and weight limits	Estimation of Vehicle Miles of Travel for truck traffic currently operating within and above existing Federal truck size and weight regulations.	Highlights: Volume 1. Technical Reports Summary, Chapter 2.1, Table 3 Technical report: Modal Shift Comparative Analysis
Subsection (a)(2) Ability of States to Recover Costs or Realize the Benefits	States could raise user fees or permit fees on vehicles operating above current Federal limits.	Highlights: Volume 1. Technical Reports Summary, Chapter 1.4
Subsection (a)(3) Frequency of enforcement violations of vehicles in excess of the Federal size and weight laws and regulations	Comparison of 13 States that enforce the 80,000 pound Federal truck weight limit with 16 States that allow higher weights under exemptions and grandfather clauses.	Highlights: Volume 1. Technical Reports Summary, Chapter 3.5.4 Technical report: Compliance Comparative Analysis
Subsection (a)(3) Cost of Enforcement	Estimations made from enforcement costs and resources data in State Enforcement Plans.	Highlights: Volume 1. Technical Reports Summary, Chapter 3.5.4 Technical report: Compliance Comparative Analysis
Subsection (a)(3) Effectiveness of Enforcement Methods	Analysis and comparison of: (1) enforcement program activities (e.g., weighings, citations, citation rates); and (2) compliance for various vehicle types.	Highlights: Volume 1. Technical Reports Summary, Chapter 3.5.4 Technical report: Compliance Comparative Analysis
Subsection (a)(4) Bridge Impacts	A structural analysis was performed on about 500 bridges representing the 12 most common bridge types. An axle-load based cost allocation approach was used to estimate costs related to different truck weight configurations.	Highlights: Volume 1. Technical Reports Summary, Chapter 3.4 Technical report: Bridge Structure Comparative Analysis
Subsections (a)(5) to (a)(6): Provisions related to Alternative Configurations: Compare and contrast the potential safety and infrastructure impacts of current Federal TSW law and regulations in relation to:
Legislative Requirement	How Addressed	Where Addressed
Subsection (a)(5) Six-axle and other alternative configurations of tractor-trailers	USDOT selected six alternative scenarios, each involving one alternative configuration and control vehicle. The methods discussed above under Section (a)(1) to (a)(4) were then applied to produce the comparison for each scenario.	Highlights: Volume 1. Technical Reports Summary,Chapter 2 Technical reports: Each of the five technical reports compares the six scenarios for the specific topic addressed.
Subsection (a)(6) Safety records of other nations with different truck size and weight limits than U.S. Federal limits	Desk scan (Literature search) of selected foreign nations.	TS&W limits in other countries: Volume 1. Technical Reports Summary, Chapter 1 Foreign country safety records: Draft Safety and Truck Crash Analysis Report, Appendix A, Safety Analysis Desk Scan, A.4 International experience.
Subsection (a)(6)(A) Freight diverted from other surface modes to principal arterial routes and NHS intermodal connectors	Mode shifts estimated using the Intermodal Transportation and Inventory Cost (ITIC) model. The Freight Analysis Framework (FAF) was the primary commodity flow data base. The Carload Waybill Sample was used for rail diversion analysis	Highlights: Volume 1. Technical Reports Summary, Chapter 3 Technical report: Draft Modal Shift Comparative Analysis
Subsection (a)(6)(A) Effect diversion would have on: other modes of transportation	Developed assumptions necessary for the modal shift analysis and identify limitations in the data and analytical methods that will affect the analysis. Estimated modal shifts associated with each scenario using the analytical tools and data chosen for the analysis.	Highlights: Volume 1. Technical Reports Summary, Chapter 3.1 Technical report: Modal Shift Comparative Analysis, Chapter 6
Subsection (a)(6)(B) Effect diversion would have on: Public safety Infrastructure Cost responsibilities Fuel efficiency	The approach taken in (a)(1) above was applied to each of the six alternative scenario vehicles and their control vehicles. The approach taken in pavement and bridge (a)(2) and (a)(4) above was applied to the scenario vehicles. See pavement and bridge descriptions in (a)(2) and (a)(4) above. Change in fuel consumption (gallons) was estimated for each scenario.	See (a)(1) above. See pavement and bridge (a)(2) and (1) (4) above. See pavement and bridge (a)(2) and (a)(4) above. Highlights: Volume 1. Technical Reports Summary, Chapter3.1.4. Technical report: Modal Shift Comparative Analysis, Chapter 5. Highlights: Volume 1. Technical Reports Summary, Chapter 3. Technical report: Modal Shift Comparative Analysis, Chapters 3 and 4
Freight transportation costs Environment	Estimation of total logistics costs for the alternative scenarios. Change in carbon dioxide emissions and oxides of nitrogen emissions were estimated for each scenario.	Highlights: Volume 1. Technical Reports Summary, Chapter 3.1.4 Technical report: Modal Shift Comparative Analysis, Chapter 5
Subsection (a)(6)(C) Effect on Transportation Network	Diversion between truck types and diversion from rail to truck under each scenario. Highway user delay and congestion costs were assessed using three traffic simulation models—one for Interstate highways, one for rural two-lane highways, and one for urban arterials.	Highlights: Volume 1. Technical Reports Summary, Chapter 3.1 and Tables 6 and 7 Technical report: Modal Shift Comparative Analysis, Chapter 6
Subsection (a)(6)(D) Increases/decreases in total number of trucks on principle arterials and NHS intermodal connectors	The study analysis used changes in VMT and did not use an estimate of trucks.
Subsection (a)(7): Identify all Federal rules and regulations impacted by changes in truck size and weight limits.
Legislative Requirement	How Addressed	Where Addressed
	Reviewed statutes and regulations on all roads/highways on which Surface Transportation Assistance Act vehicles now operate.	Highlights: Volume 1. Technical Reports Summary, Chapter 3.5.4 Technical report: Compliance Comparative Analysis, Chapter 4. 4.4.

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