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Comprehensive Truck Size and Weight Limits Study - Compliance Comparative Analysis Technical Report

Executive Summary

Background

This report documents analyses conducted as part of the U.S. Department of Transportation (USDOT) 2014 Comprehensive Truck Size and Weight Limits Study (2014 CTSW Study). As required by Section 32801 of MAP-21 [Moving Ahead for Progress in the 21st Century Act (P.L. 112-141)], Volumes I and II of the 2014 CTSW Study have been designed to meet the following legislative requirements:

  • Subsection 32801 (a)(1): Analyze accident frequency and evaluate factors related to accident risk of vehicles to conduct a crash-based analyses, using data from States and limited data from fleets;
  • Subsection 32801 (a)(2): Evaluate the impacts to the infrastructure in each State including the cost and benefits of the impacts in dollars; the percentage of trucks operating in excess of the Federal size and weight limits; and the ability of each State to recover impact costs;
  • Subsection 32801 (a)(3): Evaluate the frequency of violations in excess of the Federal size and weight law and regulations, the cost of the enforcement of the law and regulations, and the effectiveness of the enforcement methods; Delivery of effective enforcement programs;
  • Subsection 32801 (a)(4): Assess the impacts that vehicles have on bridges, including the impacts resulting from the number of bridge loadings; and
  • Subsections 32801 (a)(5) and (6): Compare and contrast the potential safety and infrastructure impacts of the current Federal law and regulations regarding truck size and weight limits in relation to six-axle and other alternative configurations of tractor-trailers; and where available, safety records of foreign nations with truck size and weight limits and tractor-trailer configurations that differ from the Federal law and regulations. As part of this component of the study, estimate:
    • (A) the extent to which freight would likely be diverted from other surface transportation modes to principal arterial routes and National Highway System intermodal connectors if alternative truck configuration is allowed to operate and the effect that any such diversion would have on other modes of transportation;
    • (B) the effect that any such diversion would have on public safety, infrastructure, cost responsibilities, fuel efficiency, freight transportation costs, and the environment;
    • (C) the effect on the transportation network of the United States that allowing alternative truck configuration to operate would have; and
    • (D) the extent to which allowing alternative truck configuration to operate would result in an increase or decrease in the total number of trucks operating on principal arterial routes and National Highway System intermodal connectors.

To conduct the study, the USDOT, in conjunction with a group of independent stakeholders, identified six different vehicle configurations involving six-axle and other alternative configurations of tractor-trailer as specified in Subsection 32801 (a)(5), to assess the likely results of allowing widespread alternative truck configurations to operate on different highway networks. The six vehicle configurations were then used to develop the analytical scenarios for each of the five comparative analyses mandated by MAP-21. The use of these scenarios for each of the analyses in turn enabled the consistent comparison of analytical results for each of the six vehicle configurations identified for the overall study.

The results of this 2014 Comprehensive Truck Size and Weight Limits Study (2014 CTSW Study) study are presented in a series of technical reports. These include:

  • Volume I: Comprehensive Truck Size and Weight Limits Study – Technical Summary Report. This document gives an overview of the legislation and the study project itself, provides background on the scenarios selected, explains the scope and general methodology used to obtain the results, and gives a summary of the findings.
  • Volume II: Comprehensive Truck Size and Weight Limits Study. This volume comprises a set of the five comparative assessment documents that meet the technical requirements of the legislation as noted:
    • Modal Shift Comparative Analysis (Subsections 32801 (a)(5) and (6)).
    • Pavement Comparative Analysis (Section 32801 (a)(2)).
    • Highway Safety and Truck Crash Comparative Analysis (Subsection 32801 (a)(1)).
    • Compliance Comparative Analysis (Subsection 32801 (a)3)).
    • Bridge Structure Comparative Analysis (Subsection 32801 (a)(4)).

Purpose of the Compliance Comparative Analysis

The purpose of this report is to assess 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.

The first three of the six scenarios asses the impacts of heavier tractor semitrailers than are generally allowed under current Federal law. Scenario 1 would allow five-axle (3-S2) tractor semitrailer to operate at a maximum gross vehicle weight (GVW) of 88,000 lb. while Scenarios 2 and 3 would allow six-axle (3-S3) semitrailers to operate at maximum GVWs of 91,000 lb. and 97,000 lb., respectively.

Scenarios 4, 5 and 6 examine vehicles that would serve primarily lower density cargoes commonly associated with those trucks that carry cargo from more than one shipper (known as less-than-truckload traffic or LTL). Scenario 4 examines twin trailer combination with 33-foot trailers (2-S1-2) with a maximum GVW of 80,000 lbs. Scenarios 5 and 6 examine triple trailer combinations with 28 or 28.5-foot trailers having maximum GVWs of 105,500 lb. (2-S1-2-2) and 129,000 lb. (3-S2-2-2), respectively.

At this point it is important to note that while the control double has an approved GVW of 80,000 pounds, the GVW used for the control double in the study is 71,700 pounds based on actual data collected from weigh-in-motion (WIM)-equipped weight and inspection facilities and is a more accurate representation of actual vehicle weights than the STAA authorized GVW. Using the WIM-derived GVW also allows for a more accurate representation of the impacts generated through the six scenarios.

Table ES-1 on the following page depicts the vehicles assessed under each scenario as well as the current vehicle configurations from which most traffic would likely shift (the control vehicles).

This Compliance Comparative Analysis is supported by a comprehensive scan of recent literature and insights obtained from TSW enforcement stakeholders and experts from around the world (Appendix A and Appendix B).

The cost analysis portion of this study includes a description of the principal TSW enforcement methods used in the United States, including the application of enforcement technologies, meaning that the enforcement costs assessed reflect the resources required to undertake the truck size and weight enforcement task. The analysis examines national-level trends in enforcement program costs and conducts enforcement cost comparisons between States and for different truck configurations. Finally, the analysis estimates the enforcement cost impacts of introducing the alternative truck configurations into the traffic stream.

Enforcement program effectiveness reflects how the resources provided to the enforcement program translate into TSW enforcement actions and ultimately contribute to achieving regulatory compliance. The effectiveness analysis examines trends and relationships pertaining to enforcement program activities (such as truck weighings) and compares effectiveness between States and for different truck configurations. WIM data gathered at sites where alternative truck configurations currently operate provide the basis for comparing the compliance impacts of introducing these configurations into the traffic stream.

Methodology

Despite the widely held notion of a linkage between truck weight enforcement and compliance, there remains an inability to fully understand this relationship because of differences in how enforcement occurs and a lack of systematic and reliable evidence concerning overweight trucking. Additionally, understanding this relationship for specific truck configurations—one of the main issues of interest in this 2014 CTSW Study—has generally been constrained by insufficient data. Increasing investments in proven enforcement technologies, including tools for identifying non-compliant trucks or carriers and the expanded use of WIM devices for monitoring truck weights, provide some opportunity to address these historical data limitations; however, certain data gaps persist which preclude a definitive analysis of the subject.

Table ES-1: Truck Configurations and Weight Scenarios Analyzed in the 2014 CTSW 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) 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) 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) 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) 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) 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) 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) 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) Tractor plus three 28 or 28 ½ foot trailers (2-S1-2-2) 3 9 129,000 Same as Scenario 5 3

1 The STAA network is the National Network (NN) for the 3S-2 semitrailer (53 feet) with an 80,000-lb. maximum GVW and the 2-S1-2 semitrailer/trailer (28.5 feet) also with an 80,000 lbs. maximum GVW vehicles. The alternative truck configurations have the same access off the network as its control vehicle. Return to Footnote 1

2 The 80,000 pound weight reflects the applicable Federal gross vehicle weight limit; a 71,700 gross vehicle weight was used in the study based on empirical findings generated through an inspection of the weigh-in-motion data used in the study. Return to Footnote 2

3 The triple network is 74,454 miles, which includes the Interstate System, current Western States’ triple network, and some four-lane highways (non-Interstate System) in the East. This network starts with the 2000 CTSW Study Triple Network and overlays the 2004 Western Uniformity Scenario Analysis, Triple Network in the Western States. There had been substantial stakeholder input on networks used in these previous USDOT studies and use of those provides a degree of consistency with the earlier studies. The triple configurations would have very limited access off this 74,454 mile network to reach terminals that are immediately adjacent to the triple network. It is assumed that the triple configurations would be used in LTL line-haul operations (terminal to terminal). The triple configurations would not have the same off network access as its control vehicle–2S-1-2, semitrailer/trailer (28.5 feet), 80,000 lbs. GVW. The 74,454 mile triple network includes: 23,993 mile network in the Western States (per the 2004 Western Uniformity Scenario Analysis, Triple Network), 50,461 miles in the Eastern States, and mileage in Western States that was not on the 2004 Western Uniformity Scenario Analysis, Triple Network but was in the 2000 CTSW Study, Triple Network (per the 2000 CTSW Study, Triple Network). Return to Footnote 3

The analysis of costs and effectiveness undertaken in this study takes a performance-based approach. This approach considers enforcement program performance (or effectiveness) in terms of inputs, outputs, outcomes, and pertinent relationships between these measures. Enforcement program inputs reflect the resources (i.e., personnel, facilities, technologies) available to carry out the TSW enforcement task. State Enforcement Plans (and the subsequent certification of these plans) submitted by each State are the principal data source used to analyze program inputs.

Outputs reflect the way enforcement resources are used, the scale or scope of activities performed, and the efficiency of converting allocated resources into a product (e.g., quantity of weighings, weight citations). These output measures are sourced from the Annual Certifications of Truck Size and Weight Enforcement database. While these outputs on their own provide some indication of program effectiveness, additional outputs and inputs can improve the overall understanding of program effectiveness.

The relationship between citation rate and enforcement intensity (measured as the number of weighings per truck vehicle-miles of travel) is one example. Outcomes reflect the degree of success of the TSW enforcement program in achieving its goal, which from an operational and programmatic perspective, is to achieve compliance with TSW regulations. The outcome measures used in this study are the proportion of axle or truck observations that fall within the Federal weight compliance limits compared to the severity of overweight observations.

Applying the performance-based approach provides the supporting framework for a comparative analysis designed to reveal insights about the costs and effectiveness of TSW enforcement programs. Data limitations, consistency, and availability constrain a comprehensive, representative understanding of these costs and effectiveness, particularly regarding vehicle-specific comparisons. To accommodate these limitations and leverage existing datasets and institutional knowledge, this study applies two types of comparisons:

  • At a broad level, readily available State-specific data provides the foundation for comparing costs and effectiveness between States that currently allow trucks above Federal weight limits and those that do not. As the State-level data used in these comparisons do not allow disaggregation by vehicle configuration, these comparisons can be understood as a surrogate way of revealing potential vehicle-specific differences at a State level.
  • A more detailed comparative analysis of enforcement program costs and effectiveness involves vehicle-specific comparisons (where possible). These comparisons focus on enforcement cost and effectiveness differences between the control vehicles and the six alternative truck configurations introduced into the traffic stream for the six 2014 CTSW Study scenarios. Thus, the results of the vehicle-specific comparisons directly support the scenario analysis, which estimates system-wide cost and effectiveness impacts that could result from the operation of the alternative truck configurations relative to the 2011 base case.

Summary of Results

Owing mainly to a lack of systematic and consistent data, prior research on TSW enforcement identifies the need for improved understanding of how enforcement resources, methods, and technologies can be effectively deployed to achieve better compliance. A configuration-specific understanding is particularly needed when considering the potential introduction of alternative truck configurations into the traffic stream, as is the case in this 2014 CTSW Study. The State-level and particularly the vehicle-specific comparisons conducted in this analysis leverage existing datasets and, together, reveal insights about potential differences in enforcement costs and effectiveness for trucks operating within current Federal sizes and weight limits versus alternative truck configurations with higher sizes and weights. Additionally, these comparisons support a system-wide estimation of overall cost and effectiveness impacts that could occur under the scenario conditions.

Key findings concerning enforcement costs follow:

  • From a national-level programmatic perspective, States spent a total of approximately $635 million (in 2011 US Dollars) on their TSW enforcement programs in 2011. Personnel costs represented about 85 percent of total costs, while facilities expenditures (including investments in technologies) accounted for the remaining costs. Technologies play an important role in TSW enforcement and are increasingly deployed by State enforcement agencies.
  • Based on the State-level comparisons, there is no indication of a change in enforcement costs that can be attributed to whether or not a State allows trucks to operate above Federal limits. Rather, differences in how States deliver enforcement programs (e.g., methods of enforcement used, technologies, intensity of enforcement) may have greater influential on total costs.
  • The vehicle-specific comparative analysis indicates that, because the alternative truck configurations have more axles or axle groups than the control vehicles (except the Scenario 4 configuration with two 33-foot trailers), they will require more time to weigh using certain standard weighing equipment and thus result in higher personnel costs.
  • When estimating cost impacts on a system-wide basis in the scenario analyses, personnel costs decrease because the reduction in VMT predicted by the scenarios necessitates fewer weighings overall (assuming the rate of weighing vehicles relative to VMT is held constant) and this outweighs the increased costs associated with weighing the alternative truck configurations. Viewed another way, the rate at which weighings occur (per VMT) or the time spent conducting a weighing could be increased under the scenario conditions for the same level of expenditures on enforcement personnel.

Key findings concerning enforcement effectiveness follow:

  • Considering national-level trends, both the weighing cost-efficiency (personnel costs per non-WIM weighing) and citation rate (citations per non-WIM weighing) decreased during the period from 2008 to 2012. The relationship between citation rate and enforcement intensity revealed that the citation rate decreases as enforcement intensity increases (i.e., more weighings per million truck VMT), but reaches a point of diminishing return. Moreover, those States that conduct a higher proportion of portable and semi-portable weighings generally have a lower overall enforcement intensity and a higher citation rate. Measuring enforcement effectiveness in terms of a citation rate is complex because both relatively low and relatively high citation rates could be interpreted as a reflection of an effective enforcement program.
  • Based on the State-level comparisons, as with the cost results, there is no indication of a change in enforcement effectiveness (as measured by the relationship between citation rate and enforcement intensity) that can be attributed to whether or not a State allows trucks to operate above Federal limits.
  • For the vehicle-specific comparison of enforcement effectiveness, an analysis of data from selected WIM sites indicates that, except for six-axle tractor semitrailers operating off Interstates, the alternative truck configurations exhibit a higher proportion of compliant GVW observations than the control vehicles—hence our use of the 71,700 lb. average GVW for those calculations involving the control double configuration. However, for all the comparisons, the intensity of overweight observations is higher for the alternative truck configurations than the control vehicles.
  • System-wide, in each of the scenarios analyzed, the impact on the proportion of total weight-compliant VMT for the control vehicle and alternative truck configuration is limited relative to the base case.

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