Longer combination vehicles (LCVs) have operated in Western States for many years. Grandfather rights in effect since 1956 have allowed those vehicles to exceed the 80,000 pound federal weight limit on Interstate Highways. Until 1991 States could determine the weights and dimensions allowed under their grandfather rights, but the LCV freeze instituted in the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA) prohibits States from increasing allowable LCV weights on the Interstate System or allowing longer LCVs on the National Network established in the Surface Transportation Assistance Act of 1982. Because grandfather rights in each of the Western States differ, allowable weights and dimensions for LCVs in most Western States vary.
As the U.S. Department of Transportation’s Comprehensive Truck Size and Weight (CTS&W) Study was nearing completion, the Western Governors’ Association (WGA) asked the U.S. DOT to analyze another illustrative truck size and weight scenario in addition to the scenarios already included in the study. The “Western Uniformity Scenario” requested by WGA would assess impacts of lifting the LCV freeze and allowing harmonized LCV weights, dimensions, and routes among only those Western States that currently allow LCVs. Specifically the WGA requested that DOT analyze impacts of expanded LCV operations assuming that weights would be limited only by federal axle load limits and the federal bridge formula, with a maximum gross vehicle weight of 129,000 pounds.
Scenario impacts are assessed using the same general methods used to analyze impacts of illustrative scenarios in the CTS&W Study, although substantial improvements in data and certain analytical methods have been made since that study. Specifically, impacts on safety; pavement, bridge, and other infrastructure costs; shipper costs; energy consumption; environmental quality; traffic operations; and railroad revenues and costs associated with expanded LCV use in Western States are estimated. States included in the analysis are Washington, Oregon, Nevada, Idaho, Utah, Montana, Wyoming, Colorado, North Dakota, South Dakota, Nebraska, Kansas, and Oklahoma. No changes in size and weight limits were assumed for California, Arizona, New Mexico, or Texas. LCVs are not allowed in these States except on a short section of I-15 in Arizona that provides continuity of LCV operations between Nevada and Utah.
Throughout the report impacts are estimated for operations of two different long twin-trailer configurations, one that would have two 48-foot trailers as specified in the WGA request, and one that would have trailer lengths of 45 feet which is consistent with the Western Association of State Highway and Transportation Officials (WASHTO) “Guide for Uniform Laws and Regulations Governing Truck Size and Weight Among the WASHTO States.” In this summary, only the impacts of the longer configuration are reported.
Estimated impacts, both positive and negative, of expanded LCV operations in the Western States are substantially smaller than impacts of nationwide LCV operations estimated in the CTS&W Study. Several factors account for these smaller impacts including the substantially lower volume of traffic that would be affected by the regional scenario, the lower weights and smaller dimensions assumed for LCVs in the Western Uniformity Scenario compared to the CTS&W Study, and the fact that at least some LCV operations already occur in each of the States analyzed in the scenario. This latter factor reduces traffic shifts to the new LCV operations assumed under the scenario and reduces infrastructure costs because the greater weights and dimensions of LCVs have already at least partially been reflected in infrastructure design.
Several types of traffic could be affected by the truck size and weight changes assumed in the scenario. These include short haul truck traffic that moves less than 200 miles, long haul truck traffic that shifts to LCVs from other configurations, rail carload traffic, and rail intermodal traffic. Table ES-1 shows 2010 freight traffic forecasts in the Western States under both current (base case) and scenario size and weight limits. Total truck traffic in the region is estimated to decrease by 25 percent under the scenario assumptions, with the vast majority of that decrease coming from the long-haul trucking sector. Less than one-tenth of one percent of rail traffic in the region is estimated to divert to LCVs under scenario assumptions.
|Base Case Traffic Volume (millions)||Volume (millions)||Percent change|
|Total truck (VMT)||18,823||14,028||-25.5%|
|Short haul truck (VMT)||1,844||1,743||-5.5%|
|Long haul truck (VMT)||16,978||12,285||-27.6%|
|Rail Carload (ton-miles)||785,399||785,181||-0.03%|
The extent to which traffic would actually shift to LCVs depends on relative transportation and other logistics costs for LCVs compared to the current mode of transportation. These relative costs, in turn, depend on specific characteristics of the shippers, the commodities being shipped, and the origins and destinations of the shipments. The Federal Highway Administration has analytical tools that estimate the influence of these various factors on mode and vehicle choice.
While the data may not reflect the actual costs that a specific firm would face when deciding which mode and which type of vehicle to use in transporting specific commodities from one point to another, they are believed to be representative of commodity movements within and through the study region.
Table ES-2 shows 2010 forecasts of truck traffic by major vehicle configuration for the base case and under scenario assumptions. Estimates of base case LCV travel rely on State-reported traffic counts and analyses of vehicle classification and weigh-in-motion data, but these data collection systems are not designed to provide statistically reliable estimates of total LCV travel. Other data sources including the Census Bureau’s Vehicle Inventory and Use Survey have been used to supplement the State reported data, but there is considerable uncertainty about the amount of LCV traffic in the scenario States. Previous studies, especially those focusing on LCV safety, have also noted this uncertainty in the extent of LCV use.
|Base Case Traffic Volume (millions)||Volume (millions)||Percent change|
|5-axle Tractor Semitrailer||14,476||3,442||-76%|
|6-axle Tractor Semitrailer||1,924||938||-51%|
|5- or 6-axle Double||1,351||750||-44%|
|6-axle Truck Trailer||626||607||-3%|
|8- or more axle Double||213||5,626||+2,541%|
Despite the fact that LCVs are allowed in all States covered by the scenario, conventional tractor-semitrailers and short twin trailers currently are estimated to account for 94 percent of total heavy truck travel in the region. If all Western States covered by the scenario adopted the scenario weight and dimension limits, there would be an estimated 76 percent reduction in travel by conventional 5-axle tractor-semitrailers, a 44 percent reduction of STAA doubles (5 or 6-axle twin trailers with maximum trailer lengths of 28.5 feet) travel, and a 25 percent reduction in total heavy truck travel. Because shipments that would divert to LCVs are longer than shipments that would not divert, the decrease in total travel is greater than the decrease in shipments by tractor-semitrailer. On a tonnage basis less than half of tractor-semitrailer shipments were estimated to divert to LCVs.
Reductions in conventional truck travel would result in large percentage increases in LCV travel. Nearly a twenty-fold increase in LCV travel is estimated if LCVs were allowed to operate in Western States according to assumptions in the Western Uniformity Scenario. Over half of that travel would be expected to occur in twin trailer combinations with 8 or more axles that can carry gross weights up to 129,000 pounds.
Table ES-3 shows how current and projected LCV use varies by the type of shipment. LCVs currently account for about 9 percent of total VMT for shipments entirely within the region. Under scenario assumptions that percentage is projected to grow to 78 percent. Currently LCVs are used very little for shipments where one or both trip ends are outside the region. Under scenario assumptions about half the VMT within the region for such shipments would shift to LCVs. This would require carriers to assemble and disassemble the LCVs for travel in States outside the region that do not allow LCVs. Clearly the ability of various types of carriers to efficiently manage such operations would vary, but the cost savings of operating LCVs throughout the region would make them attractive, even for many shipments with trip ends outside the region.
|Shipment Type||Percent of VMT in LCVs|
Changes in the amount and characteristics of truck travel under scenario assumptions would affect long-term pavement and bridge costs, and could necessitate interchange and other geometric improvements to accommodate the larger trucks. Table ES-4 shows estimates of these added infrastructure costs associated with expanded LCV operations under the Western Uniformity Scenario. Despite the fact that more LCVs with higher gross weights could be expected to operate under the scenario assumptions, total pavement costs could actually decrease somewhat. Estimates in this study are that pavement costs in the scenario States could decrease by more than 4 percent under the Western Uniformity Scenario. Several factors account for this decrease including the reduction in total truck VMT, a shift of some traffic from lower-order highway systems to the Interstate System that typically has stronger pavements, and the fact that axle load limits are assumed to continue to control loads on individual axle groups. Incremental pavement costs attributable to the scenario were estimated by calculating the difference between total pavement improvement costs over a 20-year period in the scenario States under current size and weight limits and total pavement costs assuming the estimated VMT and weight distributions under the scenario size and weight limits.
As noted in Chapter V, many factors would affect bridge costs if States were allowed to change size and weight limits in accordance with scenario assumptions. Based on information in FHWA’s National Bridge Inventory, many bridges in the Western States are being stressed beyond their design levels by vehicles operating under current State size and weight limits and permitting practices. Since bridges are designed with large safety factors, the overstressed bridges are not in danger of collapsing, but their safety margins are reduced. Based on assumptions discussed in Chapter V about long term needs to replace or strengthen overstressed bridges, base case bridge improvement costs attributable to overstress by vehicles currently operating in the scenario States range from about $1.6 billion to $3.3 billion. Incremental costs to accommodate vehicles assumed to operate under the scenario range from $2.3 billion to $4.1 billion. Thus bridge improvement costs in the region attributable to bridge overstresses are estimated to more than double under the Western Uniformity Scenario. Twenty-year average annual bridge costs to either replace or strengthen overstressed bridges were estimated by simply dividing total estimated costs by 20. In practice, States might not be able to spread bridge improvement costs over a 20 year period, but they would not have to improve or replace all bridges before LCVs could use the bridges.
|Infrastructure Element||Base Case Improvement Costs||Total Incremental Cost||20-Year Annual Incremental Cost||Percent Change in Base Case Costs|
|Bridge Improvements||High 3,257||4,125||206||+127|
* Total estimated pavement preservation cost in scenario States. Base case costs cannot be linked to vehicles with particular weights and dimensions as can bridge and geometric costs.
Incremental pavement and bridge costs attributable to the Western Uniformity Scenario are primarily related to the increased weight of vehicles operating in the region. Increases in vehicle length could affect the ability of vehicles to stay within their lanes on curves and to negotiate intersections and freeway interchanges. Like bridges, some highways have geometric design deficiencies to accommodate operations of the current fleet. For instance long vehicles may not be able to avoid running on the shoulders of some interchange ramps or may not be able to stay within their lane when traveling on winding sections of road. Ideally such geometric problems should be corrected, but within the scope of a highway agency’s total highway improvement needs, such improvements may be deferred unless they are judged to be a significant safety issue. Base case costs to improve curves, intersections, and interchanges to accommodate vehicles already operating in the Western States are estimated to be $864 million, $713 million of which is on the Interstate System. Under assumptions of the Western Uniformity Scenario, geometric improvement costs would nearly double to $1,640 million. Like bridge improvements, geometric improvements do not all have to be made before the longer vehicles could operate, but in certain locations safety could be compromised if geometric improvements were delayed. In other locations the primary impact of geometric deficiencies is higher maintenance costs, although when a vehicle cannot stay within the traveled lane there can be a potential safety problem.
In addition to infrastructure costs, there would be several other potential impacts of expanded LCV operations under assumptions in the Western Uniformity Scenario. The most important of those impacts is safety. Other impacts include traffic operations, energy consumption and emissions, and rail competitiveness.
The CTS&W Study highlighted many uncertainties that make estimating safety impacts of changes in truck size and weight limits difficult. Data on the number of fatal crashes involving LCVs are available from the National Highway Traffic Safety Administration’s Fatality Analysis Reporting System and the University of Michigan Transportation Research Institute’s Trucks Involved in Fatal Accidents databases. However, even in States where LCVs currently operate, estimating LCV crash rates is difficult because most States do not collect data on LCV travel. Estimates of LCV travel were available from several States and from some of the larger carriers that operate LCVs, but the data were not complete enough or representative enough to estimate overall LCV crash rates in the Western States. In the CTS&W Study the point was made that even if current LCV crash rates were available, those rates might not apply to expanded LCV operations because many companies that had never operated LCVs before would begin using those vehicles, many drivers with little or no previous LCV experience would begin driving LCVs, and large LCVs would be used in places where they have never operated before. Under the Western Scenario some of those uncertainties would be reduced since expanded LCV operations would be in States where LCVs currently are operating. Nevertheless, under the scenario LCVs would be operating in some States at greater weights and larger dimensions than is currently allowed and could be operating on highways they currently are not allowed to use. Even though reductions in overall heavy truck VMT estimated under the scenario would reduce crash exposure, there would still be uncertainties about the safety of expanded LCV operations that would warrant monitoring.
Without data on crash rates it is difficult to quantify safety impacts of allowing more widespread LCV operations in Western States. One set of safety-related factors that can be quantified are stability and control properties of different vehicle configurations. The analysis of vehicle stability and control characteristics conducted for the CTS&W Study was updated for this study to reflect the types of trucks currently being operated in Western States and the size and weight limits assumed in this scenario. Three specific performance measures were evaluated, static rollover stability, rearward amplification, and load transfer ratio. Those three measures, which are described in detail in Chapter VII, indicate the susceptibility of a vehicle to rollover and to rear trailer sway. Stability and control performance of most LCVs currently used in the Western States is as good or better than the performance of STAA doubles (twin 28-foot trailers) that are widely operated in all States. Performance for some configurations is comparable to that of a standard tractor-semitrailer. There are exceptions, however. Conventional triple trailer combinations, in particular, have poorer rearward amplification and load transfer ratios than other vehicles, which makes them more prone to trailer sway and rollover if they have to make a sudden turning movement.
Offsetting the relatively good stability and control properties of LCVs are the greater time required to pass an LCV, the greater offtracking of longer double trailer combinations, the heavier weight of the vehicles which places greater demands on braking systems, and operational problems that longer vehicles create in urban areas where many weaving and merging maneuvers are required.
The Western Association of State Highway and Transportation Officials has developed model regulations for the operation of LCVs, but actual regulations governing LCV operations differ significantly from State to State. Some States have comprehensive regulations covering equipment, drivers and operations while others have no special regulations that apply to LCVs or their drivers. Most States have no program to monitor LCV safety, but in discussions with State officials they did not note particular safety problems with current LCV operations. Some, however, indicated they would not allow operations of LCVs at the weights and dimensions assumed in this study, even if they had the flexibility to do so.
The CTS&W Study presented results of focus groups and surveys that indicated a general uneasiness on the part of many motorists in sharing the roads with big trucks. No additional focus group research was conducted for this project and the extent to which these findings reflect attitudes of motorists in Western States is unknown. Many non-technical factors influence truck size and weight policy decisions and public opinion certainly is one of those factors.
The increased use of LCVs estimated under this scenario could also affect traffic operations. Some reductions in congestion and delay could result from the lower truck volumes, but those benefits could be offset by decreased passing opportunities, increased delay if LCVs cannot maintain their speeds on steep grades as well as conventional trucks, increased difficulty merging and weaving in urban areas because of the greater vehicle lengths, and potential delays at intersections and other locations caused by the larger offtracking of LCVs. Many operational problems are directly related to highway geometry. If geometric improvements are made to accommodate LCVs, some operational impacts may be reduced. Adverse impacts on traffic operations affect more than traffic delay. They also can contribute to increased crash risks. A clear demonstration of this is the lower overall crash rates on Interstate highways when compared to other highways.
As shown in Table ES-5, reductions in VMT associated with the Western Uniformity Scenario could reduce fuel consumption associated with freight transportation and could also reduce emissions and highway noise. The 25 percent reduction in truck VMT associated with the scenario is estimated to result in a 12 percent reduction in fuel consumption. Fuel savings are not directly proportional to VMT reductions because fuel economy decreases as vehicle weight increases.
Reductions in heavy truck travel estimated under the scenario could also reduce noise and emissions. LCVs generally are noisier than conventional trucks, primarily because they have more tires. However the lower volume of truck travel associated with the scenario would result in about a 10 percent reduction in noise-related costs compared to the base case.
|Impact Area||Change from Base Case|
|Energy Consumption||-12 %|
|Noise Cost||-10 %|
|Emissions *||-12 %|
* Assumes changes in emissions are approximately proportional to changes in fuel consumption.
Impacts of changes in air quality caused by changes in freight transportation under the Western Uniformity Scenario are difficult to estimate because truck emissions interact with other mobile and stationary sources in complex ways. While a specific change in emissions may not lead to a corresponding change in pollutants in any given area, estimates of changes in emissions would indicate the direction in which air pollution would likely change. There has been little past research on relationships between vehicle size and weight and emissions. Changes in overall truck volumes under the scenario are not likely to cause significant changes in speeds or other traffic characteristics that affect emissions rates. The primary factor that would cause emissions to change is the change in total truck volumes and the change in traffic composition with more LCVs and fewer conventional trucks. Since other environmental, technological, and geographical factors that might affect emissions are assumed to be the same for the base case and the scenario, it is assumed for purposes of this study that total emissions vary directly with changes in fuel consumption. This is consistent with methods used by the Environmental Protection Agency to estimate heavy truck emissions in its Mobile 6 model. Therefore, emissions under the Western Uniformity Scenario are estimated to decrease approximately 12 percent from the base case. The Transportation Research Board’s (TRB’s) Special Report 267 notes, “basic data on in-use emissions of heavy trucks are extremely limited” and additional research is needed “on how truck traffic volume, the performance characteristics of trucks, and the effect of trucks on the behavior of other drivers affect emissions of all vehicles on a road.”
The largest benefits of truck size and weight changes assumed in the Western Uniformity Scenario are shipper cost savings. If more cargo can be moved in each shipment, driver, equipment, and vehicle operating costs will be lower than in the base case. Table ES-6 shows reductions in transport costs that could be realized if all changes in truck size and weight limits assumed in the scenario were adopted. For shipments currently moving by truck, the expanded availability of various types of LCVs could reduce shipper costs by as much as $2 billion per year. This represents a savings of almost 4 percent of total shipper costs for moves by truck in and through the region. Savings would be lower if some States chose not to allow LCVs to operate as widely as is assumed in the scenario. Shippers that currently use railroads also would realize savings. The actual switch from rail to truck is estimated to be small, producing savings of about $3 million annually. A greater savings to rail users would come from rate reductions that railroads would make to keep traffic from switching to trucks. These savings would be about $26 million per year.
|Source of Savings||Amount |
(millions of 2000 $)
|Truck to Truck Diversion||2,036||3.9 %|
|Rail to Truck Diversion||3||.01 %|
|Rail Discounts||26||.11 %|
Longer combination vehicles have been operating in 13 Western States for many years. Size and weight limits in those States vary as does the extent of the highway network on which LCVs can operate. Some of these differences are due to federal truck size and weight limits, especially grandfather rights under which States can allow vehicles exceeding 80,000 pounds to operate on Interstate Highways. But some of these differences also reflect differences among the States in the vehicle weights and dimensions they believe are appropriate for their highway systems. If States were given the flexibility to increase their truck size and weight limits to levels assumed in this scenario, some States immediately would take full advantage of this flexibility, others might change some but not all size and weight limits, and several might not change truck size and weight limits at all.
Like previous studies that have examined the potential impacts of changing truck size and weight limits, this study has estimated substantial shipper benefits from allowing more widespread use of LCVs. Other benefits from the changes in truck size and weight limits assumed in this scenario are reductions in fuel consumption, emissions, and noise-related costs. The full benefits estimated in this study likely would not be realized, however, because all States would not allow LCV to operate as widely as assumed in this scenario.
Infrastructure and related costs would not be as great as has been estimated in previous studies because LCVs already operate on at least some highways in each of the 13 States included in the analysis. Thus to a certain extent States have already considered LCV weights and dimensions in pavement, bridge, and geometric design. Nevertheless improvements costing several billion dollars were estimated to be needed to correct deficiencies in bridges, interchange ramps, and other highway elements just to accommodate existing truck operations. These deficiencies may not be severe enough to require immediate improvements, but in the long run would likely have to be corrected, especially if LCV volumes increased. If LCV operations expanded under assumptions in this scenario, added infrastructure costs could be from about $300 million to more than $2 billion. Several factors would affect the magnitude of these additional infrastructure costs including the extent to which States allowed larger LCVs to operate, the length limits imposed on double trailer combinations, and the extent to which bridges can be strengthened rather than replaced. Some States may continue to defer non-essential costs as they have done under current truck size and weight limits, but doing so ultimately may increase costs and could increase safety risks as well.
Few Western States charge fees that cover the infrastructure costs associated with LCV operations. The significant exception is Oregon that routinely conducts highway cost allocation studies to estimate the cost responsibility of various truck classes and adjusts truck-related fees according to results of those studies. When LCVs and other heavy trucks do not pay the full costs of their operations, other motorists must make up the difference. This is inequitable to the highway users who must subsidize LCV operations and contributes to an uneven playing field for railroads and other competitors. States already are experiencing budgetary problems as they look to improve the condition and performance of their transportation systems, and Federal Highway Trust Fund revenues to support the Federal-aid highway program have been growing more slowly in recent years. Before any action is taken with respect to changes in truck size and weight limits that could increase highway investment needs, plans for financing those improvements should be developed that include how the longer, heavier trucks responsible for additional costs would contribute to paying those costs. This is consistent with recommendations in the TRBs Special Report 267 in which it concluded, “federal legislation creating the (TRB's recommended) permit program should specify a quantitative test for the revenue adequacy of the permit fees imposed by states that wish to participate...Fees should at least cover estimated administrative and infrastructure costs for the program...”
Safety is always the issue of greatest concern when truck size and weight issues are considered. Data simply are not available upon which to develop reliable estimates of changes in the number of crashes or fatalities that might result from a change in truck size and weight limits such as the Western Uniformity Scenario. While some LCV operators claim the safety experience of LCVs is better than for the conventional vehicles they operate, these claims cannot be borne out for LCV operations as a whole. States in which LCVs operate have not noted particular safety problems with current LCV operations, but they have no formal processes in place to monitor safety. Since there are many uncertainties about the safety of substantially increased use of LCVs as might occur under the Western Uniformity Scenario, it would be prudent to require such processes before any substantial change in federal truck size and weight limits such as the Western Uniformity Scenario was implemented. In addition to monitoring the on-road safety of LCVs, processes might also be considered to ensure that the vehicles to be used meet some minimum thresholds for stability and control, and that companies operating these vehicles have good safety records and vehicle maintenance programs.
Nationwide, the Department believes that an appropriate balance has been struck on truck size and weight. Western States included in this scenario all can allow LCVs to operate at weights substantially above the 80,000-pound federal limit on Interstate Highways, and a number of other States can allow axle loads exceeding federal limits under grandfather rights. While the widely varying State laws appear to be inefficient, they are the result of political processes that have attempted to balance economic development concerns with concerns for safety and infrastructure protection. This balance has resulted in somewhat different size and weight limits from State to State, but these differences largely reflect factors unique to each State. The pattern of truck size and weight limits that has evolved over the years may not be optimal by any objective measure, but it does allow for some appropriate regional variation without compromising safety, which is the Department’s highest priority.
Many proponents of change in truck size and weight limits point to TRB’s recommendations in Special Report 267 as a blueprint for a systematic process to more nearly optimize truck size and weight policy. However, aside from certain segments of the trucking industry and several States interested in truck size and weight increases, strong support for TRB’s recommendations has not been evident. The Department has not taken a formal position on the TRB study, in part because it does not favor change in federal truck size and weight policy, but if changes were to be made, the Department believes that the kind of strong monitoring and evaluation that TRB recommends would be essential. Without support for the kind of comprehensive approach to truck size and weight policy and permitting practices recommended by TRB, there would be no mechanism to quickly identify safety or other problems that might arise.
In recent years a number of ad hoc, State-specific exemptions from federal truck size and weight laws have been enacted. For instance, TEA-21 contained special exemptions from federal size and weight limits in four States, Colorado, Louisiana, Maine, and New Hampshire. The Department does not support this kind of piecemeal approach to truck size and weight policy. It makes enforcement and compliance with truck size and weight laws more difficult, it often contributes little to overall productivity, it may have unintended consequences for safety and highway infrastructure, and it reduces the willingness to work for more comprehensive solutions that would have much greater benefits. A regional approach such as the Western Uniformity Scenario could have greater benefits than a series of individual exemptions, but it also could have much more serious adverse consequences unless closely monitored. Unless there were very strong support from State elected officials for a carefully controlled and monitored evaluation of changes in truck size and weight limits such as those in the Western Uniformity Scenario, the risks of adverse impacts from the unmonitored use of LCVs, the divisiveness that might ensue as the current balance in truck size and weight policy is upset, and the further polarization of this very contentious issue would outweigh the benefits that might be realized. Strong support from elected officials of States within the region for a change in truck size and weight limits has not been evident to date, and there is no compelling Federal interest in promoting changes that are not strongly supported by the affected States.