Semisequicentennial Transportation Conference Proceedings
May 1996, Iowa State University, Ames, Iowa

Applicability of Performance-Based Standards for U.S. Truck Size and Weight Regulations

James York and T.H. Maze

Center for Transportation Research and Education,
Iowa State University,

Countries throughout the world have or are beginning to employ a method of regulating heavy truck size and weight known as performance-based standards, which focuses on regulating size and weight based on the vehicle's interaction with traffic and the highway infrastructure. The research presented in this paper is intended to provide an overview of international experience with implementing performance-based standards. The purpose of the research is to allow United States (U.S.) transportation policy makers and the motor carrier industry to better understand how and why other countries have embraced and benefited from performance-based standards and how such a method of truck size and weight regulation might be applied in the United States. The current method of U.S. truck size and weight regulation has predominantly evolved into a prescriptive system of fixed size and weight limits regardless of the performance of the vehicle. The objective of performance-based specifications is to control vehicle size and weight through the vehicle's performance rather than through blanket limits for all vehicles regardless of their performance. This paper examines size and weight regulation in 31 industrialized countries to determine how performance standards have been employed, the positive or negative experience with the application of performance-based standards, and methods used to apply and enforce these standards. Similar to the experience of other countries, if the U.S. were to incorporate performance-based standards into federal size and weight regulations, it would probably adopt its own unique path of migration toward standards that are compatible with its own land-based trading partners. This paper consists of four sections. The first section describes the current mood towards U.S. size and weight reform and reviews the coinciding factors making size and weight reform more timely. The second section defines the types of standards used to regulate heavy vehicle size and weight. The third section summarizes the review of the truck size and weight regulations and enforcement practices of 31 industrialized countries. The purpose of this review was to provide policy makers and industry officials with examples of applications of performance-based size and weight regulations in different economies and geographical regions. The fourth section reviews the issues and challenges related to integrating a performance-based standards into U.S. size and weight regulations.


The last change to national policy on truck size and weights was promulgated through the 1982 Surface Transportation Assistance Act (STAA). Since the 1982 STAA, 14 states adopted some type of incremental expansion (state-by-state) which promoted the use of longer combinations vehicles (LCV) though special access highway systems before it was halted by the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA). However, the ISTEA freeze was only intended to provide time to examine truck size and weight policy, and ISTEA legislation even requires studies of longer combination vehicle safety, use, and economics to support the future development of new truck size and weight policy. Three Government Accounting Office (GAO) reports were prepared in response to the ISTEA legislation (1,2,3). The end of the ISTEA legislation and the need to create a new transportation authorization bill during 1997 has created an environment which is favorable for truck size and weight policy reforms. Other factors which have made the issue of size and weight regulation reform more timely include the following:

  1. The North American Free Trade Agreement (NAFTA) requires that the trading partners implement a working program to make compatible standards related to vehicle weights and dimensions within three years after the agreement went into force (4). NAFTA entered into force on January 1, 1994; thus, the program to develop compatible standards must be in place by January 1, 1997. Because the three countries have different size and weight standards at the national level, some modifications to size and weight regulation of at least two of the three countries will be necessary. Conceivably, harmonization could result from Canada and Mexico adopting current U.S. standards, but this seems unlikely since, in general, these countries currently allow the operation of larger and/or heavier vehicles than those allowed in the U.S.
  2. Prior size and weight regulation promulgated by states was based on political considerations and is a result of compromise among a number of constituent parties. Existing national legislation seeks to promote uniformity, but national legislation only loosely ties together state based regulation. These compromises were not necessarily based on safety concerns of the roadway environment, engineering concerns of the roadway infrastructure, and economic concerns of an efficient motor freight industry. In fact, some relaxation of size and weight requirements at the state level have resulted in innovative designs that fit the requirements but have had the perverse effect of increasing wear to pavements and bridges. As a result, reform would provide the opportunity to make size and weight regulation more rational and support an efficient balance among all considerations.
  3. Over the course of the history of the trucking industry, from the 1920s until the enactment of the STAA of 1982, truck weights have incrementally grown as technology has improved and as states and the federal government have relaxed size and weight restrictions. However, from the early 1980s to the present, the average gross weight of loaded trucks on highways in the United States has remained almost unchanged (5). During the same period, truck transportation technology has changed dramatically, and, due to advances in technology and safety policy, truck transportation has improved its safety record (6). Although increased size and weight limits through further regulatory reform are not inevitable, many segments of the industry want further reforms, and history illustrates that further relaxation of size and weight regulation is likely. To allow increases to occur while simultaneously providing for traffic safety and protection of highway infrastructure investments is too important an opportunity to be missed.

These coinciding factors provide an environment ripe for size and weight reform. It is, therefore, incumbent on transportation policy makers to provide size and weight reforms which support North American trade, are compatible with an intermodal transportation system, and are based on engineering and science supporting superior safety and reduced road/bridge wear performance. The above factors, and possibly others, have coincided in time and have led the U.S. Department of Transportation to reexamine truck size and weight policy (7). The U.S. Department of Transportation's Federal Highway Administration (FHWA) is currently conducting a two-phase study of size and weight policy. While many options are being considered, one option for possible reform of current size and weight regulation is to move U.S. truck size and weight regulation away from current prescriptive standards and towards standards based on the vehicle configuration's performance (8).


Truck size and weight regulation standards can be divided into three types: prescriptive standards, like those currently applied in the U.S.; parametric standards, which include parameters known to be related to performance; and pure performance-based standards. Most size and weight regulation in the U.S. is not based on pure performance tests or on performance-related parameters. They are based on historical compromises between trucking and shipping interests and state and federal highway agencies. These are prescriptive standards, and they are relatively simple to enforce.

Parametric performance-based standards include performance criteria and regulate truck size and weight based on parameters known to be related to performance. For example, some suspensions have lower dynamic loads and thus cause less road wear than other suspensions (9). Parametric performance-based standards would regulate the natural frequency and damping ratio of a suspension because these parameters have an effect on dynamic loads. These standards are enforced through tests to monitor suspension rebound rates and the ability of the suspensions to reduce or dampen rebound. Such tests are extremely difficult to apply and enforce at the roadside.

Pure performance-based regulation governs size and weight based only on performance. In this case, the vehicle designer would develop a vehicle which meets or exceeds a specific performance level. A pure performance-based standard measures either the wear the vehicle imposes to bridges and pavements or the vehicle's impact on the safety environment of the roadway. Only the vehicle's performance is regulated, not the mechanisms that make the vehicle capable of meeting the performance standard. An illustration of a pure performance standard is shown in Figure 1, which illustrates the European Directive's turning circle performance standard (10). To meet the performance standard, the vehicle must complete a 360-degree circle within a 12.5-meter radius without crossing a 5.3-meter radius inner circle. This test has the effect of regulating a combination of dimensions which impact a vehicle's ability to maneuver.


This study revealed that some countries have begun to account for differences in vehicle performance in their size and weight regulations. Based on the experiences of these countries, the following observations could assist size and weight policy makers in the U.S. in considering size and weight regulations that are tied to vehicle performance:

  1. Single-axle weight limits among the 31 study jurisdictions are generally consistent and range from 5,500 kilograms (12,100 pounds) to 13,000 kilograms (25,600). Much of the variation in these weight limits can be attributed to fact that many jurisdictions have developed subcategories of single-axle weight for steering axles, single-tire axles, and driven axles.
  2. Tandem-axle weight limits vary significantly among jurisdictions with a range from 10,000 kilograms (22,000 pounds) to 21,000 kilograms (46,300 pounds). This is attributable to axle spacing requirements to limit the weight of those tandem-axles with closely-spaced axles.
  3. Twenty-two jurisdictions have separate categories for tridem-axles and allow higher weight than tandem-axles. The weight limit of tridem-axles is also controlled by axle spacing requirements.
  4. A wide discrepancy exists among jurisdictions' maximum vehicle weight. The discrepancy appears to be linked to the complexity of the vehicle. For example, the range in maximum weight for three-axle, non-articulated trucks is 7,000 kilograms (15,400 pounds). However, the range in the maximum weight for five-axle tractor trailer combinations is 34,000 kilograms (75,000 pounds).
  5. Countries have adopted widely different bridge formulas. The differences in these formulas result in significant variation in maximum multiple-axle group (bridge) weight.
  6. Eleven jurisdictions recognize and grant higher weight limits for vehicles equipped with "road friendly" or air-ride suspension.
  7. Jurisdictions are using performance criteria related to scientific and engineering principles to control the negative effects of vehicles on the highway infrastructure and on traffic safety. These criteria include the following:

The enforcement methods used for performance-based standards are more complex than those used to enforce prescriptive standards. A review of the enforcement methods of selected countries revealed that:

  1. The development of a vehicle type approval and annual inspection infrastructure appears to be crucial to the implementation of performance-based standards.
  2. The complexity of vehicle performance tests requires that these tests be conducted away from the roadside.
  3. The existing U.S. investment in enforcement infrastructure will provide an adequate platform for monitoring performance-based criteria (such as wheelbase, axle weight and spacing, and load distribution) that can be monitored at the roadside. Additionally, this existing infrastructure could be the nucleus for certifying test stations and monitoring the credentials of vehicles that must be submitted for testing and approval.

It is extremely difficult to glean guidance from the international experience to determine the ideal set of performance-based standards to transfer to the U.S. The exact nature of the performance-based standards adopted in each country is unique and is a result of the structure of the country's economy, the historical base of size and weight regulations in the country, issues related to regional trade with neighboring countries or within multinational trading block, the design of existing infrastructure, and many other characteristics. Australia, for example, has focused its performance-based standards on safety-related performance parameters of Longer Combination Vehicles (LCVs). Longer vehicles enhance the productivity of its sparsely distributed economic base, which has a substantial portion of economic activity focusing on agriculture and natural resources. This is not unlike the western United States, where similar issues have promoted the adoption of LCVs and LCV highway networks. Similar comparisons may be made between member countries of the European Union and the coastal and industrialized regions of the U.S., where, in the case of the European Union, performance-based regulation has focused on axle loads, intermodal transfers, and vehicle maneuverability.


Ideally, decisions related to the implementation of performance-based size and weight standards would be based on a thorough benefit/cost analysis, thus allowing an optimal balance to be struck between vehicle dimensions, road user fees, and the costs imposed on the traffic safety environment and to the infrastructure through road/bridge wear. Unfortunately, the analytical framework to perform such an analysis does not currently exist. However, the FHWA is currently developing a framework for cost allocation modeling. Once this framework is developed, which is expected to be late in 1996, it will be possible to measure the implications of size and weight changes made within the current prescriptive size and weight regulation framework, assuming all things remain equal (11). Unfortunately, the ability of these models to estimate the impacts of performance-based standards which focus on safety or reduced infrastructure wear is at least problematic. For example, current pavement designs do not have inputs for vehicle suspension type when projecting the life of a pavement of a given design and thickness. The first laboratory research to begin to quantify the impacts on pavement life of variations in suspension are still underway and no definitive field tests have been planned (12). Nor do data exist to determine the impact on traffic safety of limiting such performance parameters as off-tracking or static roll-over threshold vehicles. Without measures to determine the safety impacts of changing performance related size and weight criteria, it unclear that a firm benefit-cost analysis will be possible.

The European Union, Australia, New Zealand, and other countries were faced with this same uncertainty and they still moved forward. In the U.S. the envelope of safety and bridge/road wear performance of current vehicles which meet the 1982 STAA standards is, more or less, known. If performance-based standards were embraced, future standards could be required to meet or exceed present bridge/road wear and safety performance of vehicles permitted under the STAA of 1982. Therefore, to encourage a move to such improved equipment, vehicle operators could be provided with incentives to operate vehicles which impose less wear to highway infrastructure and impose less impact on the traffic safety environment. Incentives to vehicle operators may take the form of allowing greater gross vehicle weights and vehicle configurations which can accommodate greater cargo volume.

The most significant challenge of adopting a performance-based regime will be determining enforcement standards and then effectively enforcing these standards. Prescriptive standards currently in use require only that a vehicle not exceed a certain criterion, thus making them relatively simple to enforce. Performance-based standards, however, are likely to require a certification process and an enforcement process which either randomly or periodically checks vehicles to ensure that they conform to the applicable standards and are being appropriately maintained. Clearly, there are many contentious issues relating to enforcement that will need to be resolved. A few of the most difficult issues include identifying which organization(s) should conduct the certification process, how frequently checks are performed to ensure conformance with standards and what organization(s) conduct the checks, and the restrictiveness of the certification process (e.g., only certifying a design of tractor when it is operated with a trailer of a certain design (married standards)).

Given the inherent difficulty of enforcement, the development of any performance-based size and weight regime must consider the development of a system where enforcement is manageable. Other countries have applied performance-based regulatory regimes and enforcement structures, thus illustrating that performance-based standards can be enforced. In addition, as Intelligent Transportation Systems (ITS) functions which support commercial vehicle enforcement activities are deployed, enforcement of more complex performance-based standards will become less difficult.


Performance-based truck size and weight standards are being embraced by countries throughout the world. The principle of applying performance-based standards to U.S. size and weight regulation is attractive. However, many technical, policy, and regulation administration issues regarding performance-based standards remain to be determined. For example, some of the largest technical issues which remain unknown are the level of the impacts on the highway infrastructure and on traffic safety due to performance-based standards (12). Other technical issues involve determining which size and weight attributes to regulate with performance-based standards. Some of the most important policy issues, for example, include determining whether performance-based standards should become a platform for national uniformity of size and weight standards or whether regional and state-level differences should be allowed to continue, as is currently done in the western states with LCVs. Administrative issues might include the phasing-in of performance-based standards and developing criteria for measuring compliance and determining strategies for enforcement.

Given the numerous unanswered issues, observers note that adverse responses are possible when the motor carrier industry attempts to create innovative vehicle configurations to take advantage of performance-based standards (13). These observers assert that performance-based standards should not be applied and regulation should be continued through familiar prescriptive standards. However, even though adopting performance-based standards maybe difficult, the concepts underlying performance-based standards offer too many advantages not to move forward and use a performance-based framework as a foundation for future size and weight reform.

  1. Truck Safety: The Safety of Longer Combination Vehicles is Unknown. Report GAO/RCED-92-66. United States General Accounting Office, 1992.
  2. Longer Combination Truck Drivers Controls and Equipment Inspection Should Be Improved. Report GAO/RCED-94-21, United States General Accounting Office, 1993.
  3. Longer Combination Trucks: Potential Infrastructure Impacts, Productivity Benefits, and Safety Concerns. Report GAO/RCED-94-102. United States General Accounting Office, 1994.
  4. Land Transportation Standards Subcommittee: Annex 913.5.a-1. North American Free Trade Agreement, pp. 9–17.
  5. T.H. Maze, C.K. Walter, and A.G. Smadi. Policy Issues of an Iowa Longer Combination Vehicle Network. Midwest Transportation Center, Ames, Iowa, November 1994, p. 18.
  6. T. J. Donohue. The Truth About Highway Safety. Address to the Commercial Vehicle Safety Alliance 1995 Fall Conference, Sun Valley, Idaho, October 23, 1995.
  7. Comprehensive Truck Size and Weight Study. Federal Register, Vol. 6, No. 22, February 2, 1995, pp. 6587–6590.
  8. Framework for Guiding FHWA Policy Decisions Affecting Freight Transportation. Federal Register, Vol. 60, No. 166, August 28, 1995, pp. 44539–44543.
  9. D. Cebon. Interaction Between Heavy Vehicles and Roads. Society of Automotive Engineers, Thirty Ninth Ray Buckendale Lecture, Warrendale, Pennsylvania, March 1993, p. 53.
  10. Yearbook of Road Transport Law: 1995. Freight Transportation Association Ltd., Tunbridge Wells, Kent, England, 1995, p. 199.
  11. Highway Costs Allocations Study. Federal Register, Vol. 60, No. 28, February 10, 1995, pp. 8109–8111.
  12. C.G.B. Mitchell and R.R. Addis. Dynamic Pavement Loads and Road Wear: Scientific Questions the OECD Divine Projects is Intended to Answer. Proceedings of the Fourth International Symposium on Heavy Vehicles Weights and Dimensions, Ann Arbor, Michigan, June 1995.
  13. J.R. Billing. Implementation of Vehicle Weight and Dimensions Regulations. Proceedings of the Fourth International Symposium on Heavy Vehicles Weights and Dimensions, Ann Arbor, Michigan, June 1995, pp. 107–114.

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