Table 10. Disposition of June 18, 2015, event comments.
| Topic |
Comments |
Response |
| Safety |
| The WA State data shows there were no fatalities on 6-axle trucks and fewer injuries on 6-axle trucks vs. 5-axle trucks. You chose to highlight a higher crash rate on a very small sample, but didn’t mention the lower injuries and fatalities. Why? |
Crash severity differences are included in the Safety and Crash Analysis Report and are presented on pages 30-35. |
| There are numerous references to inadequate data for truck configurations that are generally uncommon. I fear we have to conclude that any future/speculative configuration (or any transportation modification) will be DOA since there won’t be adequate data. Is it more appropriate to conclude that we didn’t build the models necessary to draw conclusions? |
From the outset, the Study was proposed as a data-driven effort. The Study teams did not anticipate the pervasive lack of accurate, complete, replicable, available data that could be extrapolated to draw national-level conclusions. There was no intent on the part of the FHWA, DOT or Study teams to do less than necessary to achieve the requirements of MAP-21. The first report of the NAS Peer Review identified potential issues for drawing national-level findings but was similarly unable to identify any better models for this purpose. |
| What is the impact of the increase in truck weights on roadside safety, i.e., roadside appurtenances? |
The Safety and Crash Analysis technical report found that current testing methods for roadside appurtenances cannot adequately assess the impacts of heavy trucks. |
| When you reference that trucks weighing more than 80,000 pounds had an 18 percent higher level of brake violations, this appears very similar to work FMCSA has long done on overweight 5-axle trucks, not properly loaded 6-axle configurations. Does this 18 percent figure apply to the two 6-axle configurations, and can you share that specific data. |
The higher level of brake violation applies to both six-axle configurations; the analysis on citations and violations lacked crash data so a comparison was made between trucks with 5 axles versus 6 axles. This data can be shared by making a request of the FHWA Office of Freight Management and Operations. |
| In a 1992 air brake performance study the NTSB found in an inspection of 15,000 brakes that the 5th axle brake on a 5-axle truck tractor semitrailer was most often out of adjustment followed by axles 4,3,2 and #1. The reason was disruption of aerodynamic air flow to cool the brakes. Since it is not just a function of added weight but adding an additional axle. I would expect that a three-axle semitrailer would frequently have defective brakes on the rear axle. Perhaps this could be addressed. I would expect an overall increase in defective brakes found on longer combination units with more axles. |
Comment noted. The research phase concluded with the release of the technical reports and is not open to modification at this time. |
| Could you go over the logic of higher weights resulting in greater numbers of truck weight measurements? |
All scenarios modeled showed a reduction in truck VMT. Under the assumption that States would keep enforcement resource levels and expenditures constant, the potential existed for enforcement to weigh more trucks. That was one way of representing the savings. |
| Maine and Vermont implemented statewide pilot programs to allow Interstate access for six-axle trucks in 2011 and have seen record low highway fatality rates following implementation. The UK implemented widespread use of heavier, six-axle trucks in 2001 and issued an extensive report in 2006 documenting impressive productivity and safety gains, yet it doesn't appear DOT made any use of this data. Can you comment? |
These referenced efforts were included in the Desk Scan phase of the project from which they informed the development and selection of the analytical framework, models and data. |
| The various data sets reviewed appear to ignore Maine and Vermont. Why? |
Data available from all States, including Maine, and Vermont, was considered and used in the Study as appropriate, within the limitations imposed by specific data. |
| I commend DOT for including specific recommendations for improving the quality of crash rate data. Do you have any plans yet to follow up on these recommendations and will there be an opportunity for stakeholders to participate in this process? |
Stakeholders may have the opportunity to participate in follow up activities if or when an entity acts to undertake subsequent research in these areas. The DOT and FHWA will conclude their responsibilities regarding this Study with the release of the final Report to Congress for the CTSWL Study. |
| Did you receive voluntary submissions of truck crash data or other data from motor carriers or trucking associations and, if so, how was this data used and evaluated? |
Data was received but not used in the Study due to its lack of completeness and adequacy for use in the intended analysis. |
| DOT/FHWA did a great job on this Study, but I do have a question on slide 24: 1) Vehicle weight reported and did not provide meaningful analysis. 2) Yet, as noted in points 2, 3, and 4 show higher violation rates correlated to heavier vehicles. 3) Then what is the basis for point 5 that indicates vehicle weight is not a strong overall factor for predicting probability of violation? |
The analysis found that violation rates were higher for heavier vehicles. When the regression model was applied to the data, weight was not identified as a strong factor in predicting the probability of receiving a citation. These are two separate analyses that were conducted and are not contradictory. |
| Pavement |
| Did you do any analysis on fire damage to the pavement? |
No, the focus of the Study was on the potential impacts of the alternative configurations on pavement condition and integrity. |
| The six-axle vehicle configurations that were studied were both reported as reducing life-cycle pavement costs. The savings are expressed as percentages. As the pavement study was for the entire National Highway System, modest percentage savings could translate to significant dollar savings. What are the estimated life-cycle savings for pavement costs in dollars as a result of six-axle trucks? |
We did not calculate such an estimate in the Study. We focused on assessing the differences between the base case and the scenarios to address the research areas outlined in MAP-21. |
| Bridge |
| Any updates to November 15, 2013, Krolak Memo Load Rating of Specialized Hauling Vehicles? |
This vehicle type and referenced topic is not within the scope of the Study. |
| Some studies have shown that the dynamic increase factor decreases for higher truck weights. Have you considered this in your analysis? |
We used the AASHTOWare® BrR software. The AASHTO Manual for Bridge Evaluation does not recognize a decrease in dynamic load allowance with increase in truck weight. This is also the case with AASHTOWare® BrR. |
| The FHWA revised its pamphlet "Bridge Formula Weights" (August 2006). Specifically, footnote 2 on page 6
is superseded and replaced with the following: "Pursuant to 23 CFR 650.3 13, all bridges must be inspected, rated to safe load-carrying capacity, and if required, posted or restricted with respect to the maximum allowable weight." |
This comment does not relate to the scope of this Study or meeting. |
| Regarding bridges, the Study document described one-time bridge costs related to accommodating study configurations as "an extreme upper bound." See page ES-7 of the bridge paper in Volume 2 of the technical report. What are the lower range and mid-range cost estimates, not just the "extreme upper bound"? |
Lower bound and mid-range costs were not calculated. The framework for estimating the costs as upper bound costs is predicated on the assumptions that were applied in developing this analysis. Lower and mid-range costs would depend on state policies and vary by state. There is no available data to calculate such estimates. |
| In estimating modal shift, the Study assumes (Vol.1, page 36) that all bridge one-time cost improvements are made and does not assume that a State would, instead, post some bridges. Given current infrastructure budgetary pressures, if some bridges are posted rather than modified, wouldn’t that result in less modal shift under the model? |
The Bridge Analysis Report includes an estimate of bridges that may need posting associated with each scenario. Refer to page 62 of the Volume I Summary Report to find: Table 10. Projected Number of Bridges with Posting Issues for the Entire NHS Inventory. It is not possible to accurately predict the number of bridges that would be posted as opposed to modified, so a straight calculation was made assuming one-time replacement. |
| Do these test vehicles fall within the HL-93 loading that States are currently designing to? Or, are these vehicles that we need to add to our State-specific design loads? |
The configurations that were studied were not specifically compared to HL-93 as the focus of the bridge areas of study was the impact on bridge posting, which is independent of design loading. Such analysis could help determine the effect of configurations in relation to HL-93. |
| Enforcement/Compliance |
| RE: Commercial Weight Enforcement Innovation Weight Methods for Detecting Vehicles -- These methods will prove essential tools for enforcement, provide data to State DOTs when considering impacts of SHVs. |
Specialized Hauling Vehicles were not included in the Study; they are out of the scope of the Study. |
| Modal Shift |
| How do you account that VMT decrease would only be short-term (e.g., in increases back to normal levels) with the assumption that traffic was kept constant in the 50 year analysis? |
These are two different scenarios. When you remove the artificial freeze on freight growth, the projected VMT levels using the alternative configurations rises and outstrips the prospective reduction within a year: For analytical purposes, the ton-miles of freight hauled were assumed to remain constant over the analysis period. Under this assumption, reductions in VMT associated with each scenario would extend throughout the analysis period. In reality, future ton-miles of freight are expected to increase, although VMT under each of the scenarios would be expected to remain lower than VMT under current limits. |
| Is modal shift expected across the board for all RR’s, or will short-lines be disproportionately affected? |
No analysis of impacts on individual railroads was conducted and there was insufficient data to reliably estimate differential impacts on short-line railroads. |
| Does the modal shift analysis assume ideal levels of efficiency, that is, 97,000 pound trucks always carrying payloads of 97,000 pounds. Did the analysis consider alternative scenarios in which less than optimal efficiency would occur? |
As shown in the modal shift chapter, not all scenario vehicles were assumed to operate at the maximum gross vehicle weight for the scenario. The operating weight distribution for each vehicle was typical of current operating weight distributions for those vehicles adjusted to reflect the maximum gross vehicle weight limit for the scenario. |
| The report indicates that very extensive consultations were undertaken with short line railroads regarding data and modeling. Were there any such consultations with shippers (companies that are neither trucking companies nor railroads)? |
We did not have extensive discussions with the shipper community. |
| Did the speaker say that the truck VMT reduction would only last for 1 year? |
Yes, the absolute reduction in heavy truck VMT was estimated to last about a year, but relative to VMT under base case truck size and weight limits, scenario VMT would be lower into the future. |
| Why is it assumed that, in terms of the net impact of the S&W shift, the VMT shift is temporary? |
The VMT shifts under each scenario would not be temporary, but the absolute reductions in heavy truck VMT would be expected to be temporary. In the long term total truck VMT would be expected to increase, but VMT under scenario size and weight limits would remain below VMT under existing size and weight limits. |
| Miscellaneous |
| Can you provide the axle spacing and weights for the cases that were used? |
That information is found in the Safety and Crash Analysis Report on pages 56 and 57 of the Vehicle Stability and Control section. |
| Relative to my comment above, we don’t have any operational networks of 5.9 DSRC/Connected Vehicles -- yet NHTSA and RITA have documented detailed (albeit modeled) crash reductions. |
Comment noted; no reply required. |
| CTSWL = Comprehensive Truck Size And Weight Limits • DOT = U.S. Department of Transportation • FHWA = Federal Highway Administration • FMCSA = Federal Motor Carrier Safety Administration • MAP-21 = Moving Ahead for Progress in the 21st Century Act • NAS = National Academy of Sciences • NHTSA = National Highway Traffic Safety Administration • NTSB = National Transportation Safety Board • RITA = Research and Innovative Technology Administration • RR = Railroad • SHV = specialized hauling vehicles • UK = United Kingdom • VMT = vehicle miles traveled |
