Chapter 4
Mitigation

Opportunities for mitigating the harmful effects oftruck traffic and conflicts between trucks and cars on the nation’s highways are surveyed in this chapter. The committee considered mitigation relevant to its charge because evaluation of size and weight regulations must encompass consideration of alternative or complementary means of accomplishing the regulatory objective—to control the costs of truck traffic while allowing for efficient freight transportation.

The term mitigation is used here to refer to practices or policies designed to accommodate large trucks, either those already on the road or new trucks allowed by future changes in regulations. This definition is extremely broad, since it includes any action taken by public or private parties to improve efficiency or control the costs of truck transportation. Government road authorities employ an array of regulations and practices for this purpose that apply to each component of the highway transportation system: drivers (for example, commercial driver licensing requirements); vehicles (for example, size and weight regulations, motor vehicle safety standards, and pollutant emission standards); and roads (for example, design standards governing pavement and bridge strength and geometric layout, and bridge and pavement management systems that monitor truck-induced wear).

The review in this chapter is not comprehensive. It is limited to three categories of measures that are closely linked to size and weight issues:

  • Changes made in vehicle design to reduce accident risk or highway infrastructure wear—Size and weight policy proposals, including those of past TRB studies, often have included recommendations that changes in size and weight limits be accompanied by vehicle design requirements intended to offset potentially harmful consequences of the changes. The rules of state overweight permit programs sometimes incorporate such requirements. Research is active on design improvements that could overcome certain of the undesirable properties associated with greater size and weight.



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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 Chapter 4 Mitigation Opportunities for mitigating the harmful effects oftruck traffic and conflicts between trucks and cars on the nation’s highways are surveyed in this chapter. The committee considered mitigation relevant to its charge because evaluation of size and weight regulations must encompass consideration of alternative or complementary means of accomplishing the regulatory objective—to control the costs of truck traffic while allowing for efficient freight transportation. The term mitigation is used here to refer to practices or policies designed to accommodate large trucks, either those already on the road or new trucks allowed by future changes in regulations. This definition is extremely broad, since it includes any action taken by public or private parties to improve efficiency or control the costs of truck transportation. Government road authorities employ an array of regulations and practices for this purpose that apply to each component of the highway transportation system: drivers (for example, commercial driver licensing requirements); vehicles (for example, size and weight regulations, motor vehicle safety standards, and pollutant emission standards); and roads (for example, design standards governing pavement and bridge strength and geometric layout, and bridge and pavement management systems that monitor truck-induced wear). The review in this chapter is not comprehensive. It is limited to three categories of measures that are closely linked to size and weight issues: Changes made in vehicle design to reduce accident risk or highway infrastructure wear—Size and weight policy proposals, including those of past TRB studies, often have included recommendations that changes in size and weight limits be accompanied by vehicle design requirements intended to offset potentially harmful consequences of the changes. The rules of state overweight permit programs sometimes incorporate such requirements. Research is active on design improvements that could overcome certain of the undesirable properties associated with greater size and weight.

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 Separation of car and truck traffic—This direct approach to counteracting the conflicts between car and truck traffic recently has received greater consideration and limited application. Enforcement of size and weight regulations—Effective enforcement is among the most important government activities mitigating the costs of truck traffic. If vehicles exceeding the limits (either illegally or legally with permits) are common, the characteristics of this traffic will be a major determinant of costs, and the nominal statutory limits will have reduced significance. Evaluation of changes in size and weight regulations should include consideration of the practicality of enforcing the new rules. Certain mitigation actions not discussed in this chapter are described in Chapters 2 and 3: More intensive bridge management, inspection, and maintenance as an alternative to bridge posting or replacement to accommodate heavier loads; Construction of heavier, more durable pavements, which conceivably could reduce the total cost of truck traffic; and Close matching of highway user fees to the costs caused by each user, a potentially highly effective means of controlling costs by giving truck owners economic incentives to manage their operations in ways that reduce costs to the highway agency and other road users. Other important categories of measures, such as truck driver regulations, were not considered by the committee. The review in this chapter shows that a number of recent developments, including new technologies and new administrative arrangements, hold promise for reducing the costs and risks of truck operation and improving the effectiveness of regulatory enforcement and monitoring. Efforts in other countries to reduce truck costs and reform regulations, in particular the program of the National Road Transport Commission (NRTC) in Australia described in Chapter 3, may provide useful models for the United States. While enforcement of size and weight regulations in the United States has been imperfect, a proliferation of special permit operations and exemptions, where these privileges are not adequately monitored, may be as significant for the effectiveness of the regulations as are illegal operations. Nonetheless, the diversity of operating environments across U.S. roads implies that some flexibility in the regulations is necessary to derive the greatest benefit

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 from the road system. One way of providing such flexibility would be to move toward the performance-based standards approach to regulations, reinforced by user fees that reflect the costs that each vehicle generates (see Chapter 3). The vehicle identification technology described later in this chapter would provide some of the capabilities needed to manage such a regulatory system. Vehicle design improvements, separation of car and truck traffic, and enforcement as means of mitigating the impacts of truck traffic are addressed in the first three sections below. In each case, policy recommendations of others, current research, and recent innovations are described. A summary is presented in the final section. VEHICLE DESIGN How truck dimensions are related to handling and stability is described in Chapter 2. As an example, adding payload to a truck will generally raise its center of gravity, reducing the truck’s rollover threshold (the lateral acceleration the truck can withstand without rolling over). In past studies, it has been argued that such linkages between truck dimensions and performance imply a connection between dimensions and safety. The TRB Twin Trailer Trucks study committee, for example, concluded: Studies of the performance and handling characteristics of large trucks show that compared with tractor-semitrailers, twins are prone to experiencing rear trailer rollover in response to abrupt steering maneuvers, provide less sensory feedback to the driver about trailer stability, tend slightly more to encroach on outside lanes or shoulders on curves at highway speeds, and undergo greater rear-end sway during routine operations…. Taken together, these special handling characteristics are mechanisms that could lead to a higher accident rate for twins operating at highway speeds. However, it is not possible to tell from vehicle handling observations alone how differences in handling affect the frequency of accidents in on-the-road experience. (TRB 1986, 3–4) The relationship between accident risk and truck handling and stability has not been established by research, as also noted in Chapter 2. Only a few studies have attempted to measure the relationship directly. Studies comparing the accident involvement rates of double-and single-trailer configurations—the most extensive body of research

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 on the safety effects of a particular vehicle feature linked to handling and stability—also fail to provide strong support for the existence of such a relationship. If truck handling and stability are related to accident risk, they are relevant to the safety of all large trucks operating under existing size and weight regulations, not just to the matter of mitigating the consequences of increasing the limits. A recent review of truck rollover research concludes that “the rollover threshold of loaded heavy trucks extends well into the ‘emergency’ maneuvering capability of the vehicle and sometimes into the ‘normal’ maneuvering range” (Winkler 2000, 2). This conclusion implies that for some types of trucks, there is a risk of rollover in the course of maneuvers that must be performed routinely. Other potential costs of increasing truck size and weight can be mitigated or avoided by attention to truck design. For example, engine size determines acceleration capability, one of the factors influencing how trucks affect traffic congestion; likewise, suspension and tire characteristics and the spacings of axles affect pavement and bridge costs. Some of these relationships are described in Chapter 2 as well. The first subsection below summarizes past proposals for combining changes in size and weight limits with requirements for vehicle-based mitigation measures. The second subsection describes evaluations and demonstrations of such measures. Mitigation Recommendations of Past Studies Proposals for reform of truck size and weight standards in the United States, Canada, and Australia have included provisions that would fit the definition of mitigation measures stated above. These studies have followed two different lines of reasoning in arriving at their recommendations. In the TRB Truck Weight Limits study (TRB 1990a, 231–232), special safety requirements are presented as a quid pro quo arrangement. That is, issuance of the vehicle permits recommended in the study would be used as an incentive to induce carriers to adopt safer practices: “The states should use the permit process to aggressively promote safety by establishing restrictions and by revoking the permits of carriers with serious or repeated safety violations.” The Truck Weight Limits study committee recommended that standards be imposed on permit vehicle designs regarding power requirements for acceleration and hill climbing, brakes, connecting equipment between the tractor and semitrailer and between the two trailing units in a double-trailer configuration, axle width, and tires and rims. It also

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 recommended that there be special requirements regarding driver qualifications and reporting of accidents involving permit vehicles. The Roads and Transport Association of Canada (RTAC 1986) developed standards defining common vehicles to be employed in interprovincial trucking throughout Canada. It adopted the performance standards philosophy: that liberalization of limits is acceptable provided certain fundamental safety and road compatibility conditions are maintained. The results of a program of vehicle testing and simulation modeling of vehicle dynamics supported RTAC’s recommendations. The Canadian study’s recommendation for weight limits for double-trailer configurations illustrates how RTAC applied the performance standards concept. The study evaluated three alternative forms of coupling between the two trailers, called the A-, B-, and C-train configurations. The B-train has a fifth-wheel coupling device permanently affixed at the rear of the frame of the first trailer; in the A-train and C-train configurations, the coupling device is a detachable dolly between the trailers. The study’s maximum weight recommendation for the B-train is higher than for the A-train and C-train configurations. Research showed that the B-train configuration is less susceptible to high-speed offtracking (that is, the rear trailer’s wheels follow the path of the tractor axles more closely during a high-speed turn) and more resistant to rollover than the other double-trailer configurations, and that its performance according to these measures is equal to that of existing tractor-semitrailers (RTAC 1986, 13). Regarding the safety significance of such differences, RTAC concludes: “Many of the differences in performance are seen as implicating higher or lower safety risks. Although it is not generally possible to quantify the magnitude of the safety risks, there is good reason to believe that the probability of involvement in certain kinds of accidents is significantly higher with some types of vehicles than others…” (p. 11). For a specified double-trailer configuration, high-speed offtracking and rollover susceptibility tend to increase with weight (RTAC 1986, 34; TRB 1990b, 100–103); therefore, allowing greater weight in the B-train, as RTAC recommends, offsets some portion of that configuration’s advantage over the other double-trailer designs. The apparent rationale for the recommendation is that B-trains can operate at a greater maximum weight than the other double-trailer configurations without exhibiting a higher rate of stability-related accidents (RTAC 1986, 17). The intended effect of the B-train weight limit recommendation is to promote use of this vehicle design and consequently to mit-

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 igate the possibly hazardous consequences of expanded use of double trailers. NRTC is developing a proposal for comprehensive reform of vehicle dimension standards in Australia that also applies the performance standards concept (ARRB 2000). Initial plans called for considering the development of vehicle performance standards organized into five categories: Safety, Access (i.e., compatibility with the roadway and with other traffic), Infrastructure impact, Truck freight productivity, and Environmental impact. The safety category includes 19 safety-related performance measures regarding stability, braking performance, mechanical integrity, and speed and acceleration capabilities (Stevenson 1999). The NRTC uses a diagram that it calls a “performance map” to illustrate its performance standards concept (NRTC 2000a, 54–55). The diagram shows the trade-off between two performance measures for a class of vehicles. For example, in Figure 4-1 (Stevenson 1999), the points at the vertices of the triangle plot the load transfer ratio (a safety performance measure) on the vertical axis with respect to gross weight (a productivity performance measure) on the horizontal axis for three truck-trailers. The load transfer ratio is a measure of the fraction of a vehicle’s weight that shifts to the outer wheels during a specified turning maneuver and is related to the likelihood of rollover. The oval represents the range of variability in these two performance measures among the population of truck-trailers; the horizontal band is the range within which the minimum acceptable load transfer ratio value is judged to lie. The lower left vertex is a truck-trailer with conventional steel spring suspension. The upper left point is a vehicle of the same configuration and weight, but equipped with air suspension, which improves the vehicle’s load transfer ratio. The lower right point is a truck-trailer with air suspension and a higher gross weight. Its load transfer ratio is no worse than that of the vehicle with conventional suspension and lower gross weight. The diagram is intended to convey the performance standards philosophy that it is acceptable to allow productivity measures (in this example, gross weight) to increase as long as the vehicle remains within the performance measure thresholds.

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 FIGURE 4-1 Application of performance standards. (Adapted from Stevenson 1999; used with permission.) A similar performance standards framework has been put forth as the basis for international harmonization of size and weight regulations under NAFTA (LTSS 1999). A minimum allowable rollover threshold regulation was recently proposed by the government in New Zealand (Land Transport Safety Authority 2001). The goal of programs for the development of performance standards is not enactment of regulations setting standards for each performance measure, to be enforced on vehicles in use. There would be no practical way, for example, to measure a truck’s load transfer ratio during a roadside inspection. Instead, performance standards would be implemented through approval of packages of standard vehicle specifications on the basis of tests showing that the standard vehicles could meet specified threshold values of the performance measures. The vehicle specifications would address length, width, coupling design, suspension design, tire characteristics, power requirements, and other features. The performance measures would provide the justification for these specifications. The specifications thus would be

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 performance-based standards as defined in Chapter 3. Presumably, operators or manufacturers could devise and seek approval for new vehicle specifications that met the performance measure thresholds. All of the above proposals involve linking size and weight liberalization to vehicle redesign in order to maintain acceptable levels of performance with respect to accident risk and other costs of truck traffic. This approach appears promising, but the credibility of the proposals suffers from the lack of quantitative estimates of the costs and benefits of the vehicle design features and other mitigation measures contemplated. Consideration of Figure 4-1 reveals the necessity of cost and benefit estimates. Even if it is assumed that a high load transfer ratio value increases accident risk (a relationship that has not been established empirically), there is no way to tell from the diagram which of the three truck types is superior from the standpoint of overall public welfare. If the safety gains of a low load transfer ratio are large, the truck with lower gross weight and superior load transfer ratio may be best instead of the vehicle with high productivity and safety no worse than that of the baseline vehicle, which is the preferred choice according to the performance threshold approach. Research and Evaluation Programs The development of methods for improving the stability of tractor-semitrailers and double-trailer combinations has been an active area of research since at least the 1970s. In the past decade, one focus of this research has been the application of electronics and information technology to improve vehicle performance. Research has been active as well on the relationship of vehicle dynamics, as influenced by suspension and tire characteristics, to infrastructure costs. One major objective of the safety research in this area has been to reduce the risk of rollover accidents. The susceptibility of a large truck to rollover is affected by its weight and configuration. The relationship among load, center-of-gravity height, and rollover threshold was noted above. In a multitrailer combination, the rearmost trailer may roll over as a consequence of rearward amplification, a “crack-the-whip” phenomenon in which the rear trailer sways laterally in response to a steering maneuver. It is because of these relationships that all of the regulatory recommendations reviewed in the preceding subsection include some provision for reducing susceptibility to rollover. Although much effort has been devoted to studying the relationship of vehicle design to dynamic behavior, few efforts have been made to

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 measure the relationship of dynamic properties to accident risk. As described in Chapter 2, research has shown a correlation between rollover threshold (the lateral acceleration a truck can withstand without rolling over) and accident rate (Ervin and Mathew 1988; Mueller et al. 1999), although the relationship appears to be weakly supported by the available data, so that the magnitude of the risk is not well known. Some examples of vehicle design research are described below. These examples indicate the promise of technological advances in vehicle design for mitigating truck impacts, as well as the obstacles to be overcome. Industry Concept Vehicles The FACT experimental vehicle, a specification for a six-axle tractor-semitrailer with tank body proposed by two manufacturers in 1989, is described in Chapter 2. According to its designers, the vehicle would show at least a 25 percent improvement in rollover threshold compared with then-standard tankers [0.45 to 0.50 g (acceleration of gravity) compared with 0.36 g]. Thus the FACT vehicle would be substantially more resistant to rollover, even though its gross weight would be 88,000 lb, 10 percent above the federal maximum weight, and its cargo capacity would be 13 percent greater than that of existing tankers (Klingenberg et al. 1989). The improved rollover threshold is achieved primarily by lowering the height of the fifth-wheel connection between tractor and trailer and increasing the width of the axles from 96 to 102 inches. The lower fifth-wheel height is made possible by the use of air suspension on the tractor. The proposal represents an adaptation to U.S. conditions of TOPAS, a concept vehicle developed in Europe by Daimler-Benz with German government support (Weatherly 1988). The FACT proposal did not lead to widespread changes in vehicle design. Attracting both market support and government regulatory sanction for the proposal would have been a complex undertaking. More recently, one of the developers of the FACT vehicle proposed another concept vehicle called Argosy, a six-axle tractor-semitrailer designed for low-density freight, with a 58-ft semitrailer (longer than any in common use today) and 90,000 lb maximum gross weight. The vehicle is reported by the manufacturer to have improved rollover resistance and an electronic suspension control feature that gives it acceptable cornering maneuverability during low-speed turns in spite of its trailer length (Moore 1998). Once again, the proposal has apparently failed to attract strong public or private interest.

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 DOT Evaluations of Information Technology Applications DOT, as part of its Intelligent Vehicle Initiative, has under way three field tests of information technology and electronics applications designed to improve truck safety, described in the following subsections. The tests are organized as partnerships between DOT and the private participants and are intended to facilitate the transition of the applications from research and development to commercial deployment. They are thus a critical step in a nearly two-decades-long development program involving vehicle and equipment manufacturers, researchers, and the government. In their organizational aspects, these tests provide possible models for pilot studies for evaluation of new truck types and alternative size and weight limits as proposed in Chapter 3. An important distinction, however, is that the pilot studies described in Chapter 3 would constitute a formal, established element of a regulatory process. That is, states, carriers, or others seeking federal authorization of the use of new vehicles or of other changes in size and weight regulations could instigate pilot studies under the control of the Commercial Traffic Effects Institute described in Chapter 3. The Institute would be then be required to recommend to the Secretary of Transportation or to the Congress, on the basis of the outcome of a pilot study, whether the associated change in the regulations would be justified. The total cost of the three tests will be $14 million. The larger tests are designed as controlled experiments and will generate sufficient experience to support direct estimates of safety benefits. Results are to be available by 2003 (DOT n.d.). Electronic Braking Systems and Collision Avoidance Electronic braking systems (EBS) represent a potential breakthrough technology for mitigating the stability problems of combination vehicles. In conventional brake systems, pedal pressure is transmitted pneumatically to the brakes. In EBS, pedal pressure is translated into an electronic signal that is sent to the brakes on each wheel. Present EBS translate this signal into pneumatic pressure at the wheel to activate the brakes. In future systems, an electric motor at each wheel may be activated to apply the brakes, eliminating any fluid pressure in the operation. Two forms of potential benefits are being evaluated. First, the technology is intended to improve the ability of the driver to slow and stop the truck quickly and without loss of control. One source of improved stopping ability is that the brakes on the rearmost axles are activated more rapidly than is the case with present pneumatic-only

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 systems, resulting in greater control and shorter stopping distance. Second, EBS can be employed to apply brakes automatically and selectively to maintain vehicle control during maneuvering. Microprocessors can receive data from each wheel regarding load, instantaneous tire traction, and other factors and compute the optimal braking force for each wheel. Systems in development are designed to use this capability not only to improve stability when the driver is braking, but also to avoid rollover and dampen rearward amplification during turning, lane changing, or evasive maneuvering, regardless of whether the driver is applying the brakes. U.S. manufacturers now offer EBS as an option on their newest trucks (to improve performance during driver-initiated braking) (Cullen 1999), and EBS for trailers may be offered soon. Present federal vehicle regulations pose some deterrents to the technology’s adoption; however, revisions to the standards in question are under consideration. The technology also is in commercial use in Europe. In the Intelligent Vehicle Initiative trial, the ability of EBS to avoid or mitigate the severity of crashes by reducing stopping distance and improving stability during braking is being evaluated. EBS is combined with disc brakes on the test trucks in an effort to further improve braking performance. Drum brakes are standard on U.S. trucks today. Trucks in the trial also are equipped with a collision warning system that uses radar to detect impending collisions and warn the driver, and a system that automatically slows the truck to avert a collision, provided the truck’s cruise control is activated. There are 97 trucks in regular revenue service involved in the trial, including control vehicles with conventional brakes and conventional cruise control. The private-sector participants include a carrier and a truck manufacturer. Rollover Avoidance Systems A field trial of two related systems intended to reduce the risk of rollover is being conducted. The Rollover Stability Advisor system senses when the lateral acceleration of the vehicle is approaching the vehicle’s rollover threshold and issues a warning to the driver (Winkler 2000, 14). The Rollover Stability Controller system extends this capability by automatically intervening to slow engine speed when the threshold is approached. In future trucks with EBS (not included in these tests), such a system could control the application of the brakes differentially at each wheel to avert rollover. The study team includes a truck manufacturer, a truck components manufacturer, a carrier, and the University of Michigan Transportation Research Institute. Six trucks in commercial use are fitted with the devices.

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 Creation of a federally managed program for systematic collection of data on violators that would identify the responsible carrier or other operator so repeat offenders could be targeted. It is acknowledged in the report that evaluation of these proposals would be necessary before they would be ready for implementation. Although one member of the Truck Weight Limits study committee dissented from the report on matters concerning analysis of enforcement issues, that member endorsed this list of possible reform measures (p. 278). National Road Transport Commission NRTC is developing model legislation for the reform of enforcement of truck regulations in Australia. (The function of NRTC is described in Chapter 3.) Despite the institutional differences between the two countries, the principles of the NRTC proposal might be taken as a model for U.S. reforms as well. The elements of the proposal are as follows (NRTC 1999; NRTC 2000b): Unified and consistent procedures for enforcement of size and weight regulations, as well as vehicle and driver safety regulations. Procedures for targeting enforcement to operators and locations where violations are most likely. Introduction of schemes for self-enforcement, which NRTC calls “alternative compliance.” In the case of weight enforcement, operators would seek accreditation by showing that they had their own auditable load-control systems. Accredited operators would be subject to periodic audits of their weight records, but would experience reduced frequency of stops for weighing on the road. Roadside enforcement would be focused on nonaccredited operators. Use of privilege-based strategies, such as making eligibility for special permits dependent on a low rate of violations. New training programs for enforcement officers and for industry. Systematic monitoring of enforcement effectiveness. Provisions to hold accountable the parties responsible for the offenses. In the case of weight laws, the shipper might be a responsible party. Appropriate severity of fines and other penalties. Nationally consistent practices among the jurisdictions responsible for enforcement to facilitate investigation and court proceedings.

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 This proposal is awaiting action by the national and state legislatures. Some jurisdictions have adopted certain of its elements. Information Technology Applications for Enforcement The Truck Weight Limits and OIG recommendations call for expanded use of WIM, which was the only prominent technological enforcement aid available at the time the two reports were written. In the past decade, information and communications technologies with the potential to revolutionize the enforcement of highway regulations have been applied in trucking. Technology applications could greatly facilitate the administration of more complex size and weight regulatory approaches and enforcement schemes—including the permit programs that exist today, as well as the federally supervised permitting proposed in Truck Weight Limits, self-enforcement such as the NRTC alternative compliance scheme, and performance standards. The purpose of the following discussion is not to suggest that technology is the solution to the enforcement problem. The information technology applications described below can be valuable enforcement tools, but will not by themselves overcome institutional obstacles to effective enforcement. The three enforcement reform proposals described in the preceding section emphasize the development of political support and legal mechanisms as the fundamental needs. The first subsection below describes existing automated clearance systems, which approve vehicles for bypassing of enforcement stops. These systems illustrate the value and present state of development of the relevant technologies. The second subsection lists some possible future extensions of these applications, and the third identifies the need to improve the databases that serve as the foundation of any automated enforcement system. Clearance Systems Automatic clearance systems, which screen trucks on the road and allow those that meet certain criteria to bypass enforcement stops, can increase enforcement efficiency in three ways: officers can concentrate their efforts on trucks that are more likely to be in violation; some enforcement functions are automated, reducing their cost; and the cost of enforcement to carriers who obey regulations is reduced. The most extensive such system in the United States is PrePass, which allows certified commercial vehicles to bypass designated weigh stations and port-of-entry facilities (where states, in addition to weighing, check that trucks entering the state comply with registration, fuel tax reporting,

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 and other state requirements). As a truck that is enrolled in the program approaches a PrePass-equipped station, a transponder in the vehicle communicates with a terminal at the station, and the truck’s weight is checked automatically as it traverses a WIM installation. If the computer verifies that the truck’s credentials are in order and its weight is legal, the transponder in the truck displays a green light to the driver and sounds a tone. A red light alerts the driver to pull in to the station. The PrePass program is administered by a nonprofit corporation governed jointly by motor carriers and the states. It is funded by transaction fees paid by the participating carriers. PrePass began operation in 1995 and has 170,000 vehicles enrolled. It is deployed at 181 sites in 21 states and continues to expand (PrePass n.d.). Another multistate program, Norpass, is in operation in other states, and some states have their own independent systems. PrePass’s voluntary public–private structure places certain limits on its application. It is not used to collect tolls, and if a carrier found that information in such a system was causing enforcement officials to single it out for greater scrutiny, it could respond by dropping its enrollment. Possible Extensions of Applications PrePass is one example of a technology with broad potential applications. Similar automatic vehicle identification (AVI) technology is already being used for toll collection. Extended applications would require enhancement of technical capabilities, greater investment in hardware by industry and public agencies, and probably new organizational arrangements. Conceivable extensions include the following: Permit enforcement—AVI could be employed to verify that the conditions of a truck’s permit matched operations with respect to weight, dimensions, or route restrictions without requiring the truck to stop. Use of a transponder could be made a requirement for certain types of permits. PrePass may in the future have some capability to check permits, but the states do not presently enter permit information in the database of credentials against which vehicles are checked. A dense network of sensors would be required for effective enforcement of route restrictions, while PrePass installations are located mainly along major Interstate corridors. Repeat offenders—Studies of weight enforcement have revealed the high proportion of violations accounted for by repeat offenders, but the states lack effective means of targeting enforcement at these

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 offenders. Requiring repeat offenders to employ transponders on their vehicles would allow states to intensify observation of this population and would in itself serve as a deterrent. Automated enforcement—With existing technology, it is possible for systems on board a truck to monitor the truck’s weight, routes, and hours of operation continuously. This information could be recorded and made available to enforcement officials or transmitted by the truck to roadside stations. Mandatory automatic recording of driver hours of service has been proposed as a regulatory requirement by the National Transportation Safety Board. On-board weighing devices are commercially available, and vehicle tracking with the Global Positioning System (GPS) is widely used in the industry, so trucks could similarly record weights and locations to demonstrate compliance with permit requirements. Evaluating the cost-effectiveness of such schemes would require planning studies and pilot implementations. Capabilities that could be added to existing systems would be the most immediately practical; for some applications, however, such as tagging of repeat offenders, the voluntary public–private organizational model would not be applicable. Databases and Information Systems Enforcement officials recognize that databases and information systems are the key to improving enforcement efficiency. The needs include data on the histories of inspections and violations of size and weight, safety, and other truck regulations; a database showing the connections among vehicles, drivers, and carriers; and records of credentials, including registrations and special permits with their restrictions. Data must be accessible in the field, comprehensive, and current. Some examples illustrate the limitations of present information systems: As noted above, the states today cannot automatically check for compliance with special permits at PrePass sites or other WIM installations. Some states are beginning tests of this capability. States do not routinely check the safety records of permit applicants. Until recently, no database existed that would have allowed a state to perform such a check. DOT has now created a national database of carrier safety information, although its coverage remains incomplete.

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 The majority of states do not track drivers or carriers who are repeat weight violators, nor do they routinely check for past weight violations when issuing overweight permits. When a citation for a weight violation is issued at the roadside, the driver is named, and the citation in general does not record carrier or shipper identity. Therefore, it is nearly impossible in most states to identify repeat offenders (either drivers or carriers) for increased scrutiny or to impose graduated penalties. Although the remaining limitations are important, progress has been made in recent years toward developing information systems for enforcement. The assembly and updating of the safety and credentials databases needed to perform real-time clearance of vehicles in systems such as PrePass are the product of a national undertaking. Through the Commercial Vehicle Information Systems and Networks (CVISN) program of the DOT’s Intelligent Transportation Systems initiative, the federal government, the states, and industry have cooperated in designing and maintaining the database (FMCSA 2000). Progress on information systems can build on these existing organizational relationships. An integrated data system that recorded size and weight enforcement history as well as safety enforcement history by carrier would provide support for new enforcement strategies. DOT maintains and publishes safety ratings for interstate motor carriers. The ratings are derived from carrier accident experience and the results of safety inspections that check compliance with vehicle, driver, and safety management regulatory requirements (FMCSA n.d.; 49 CFR 385). Inclusion of weight violations in the determination of a carrier’s safety rating has been proposed. The rationale is that a correlation is believed to exist between a carrier’s size and weight violations and accident risk. DOT can require carriers with poor safety ratings to suspend operations. The ratings also affect the intensity of the enforcement effort directed at carriers and presumably have some competitive significance since they are published. Therefore, carriers would have strong incentives to avoid reducing their ratings through overweight violations and might be less inclined to view overweight fines as a cost of doing business. It would be necessary to evaluate such a combined rating to ensure that the practice did not detract from the utility of the rating as an indicator of accident risk. SUMMARY Promising new techniques for reducing the costs of truck travel, including safety costs, are becoming available. If these techniques prove

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 to be effective, substantial cost reductions may be possible, regardless of whether size and weight limits are liberalized. Conceivably, these techniques also could substantially alter the costs and benefits of liberalizing the regulations, for example, by reducing concerns about the possible hazards associated with the handling and stability properties of larger trucks. The techniques now emerging include improved vehicle designs for better control and stability, information technology applications for control and stability and collision avoidance, streamlining the implementation of technology applications to improve enforcement, and changes in highway design. The benefits of most of these techniques in practice have not been measured, however. More effective research, monitoring, and evaluation will be essential to progress in reducing the costs and increasing the efficiency of truck transportation. The new mitigation techniques can be expected to yield benefits only if they are properly evaluated during development and implementation. Progress on mitigating truck costs will depend on the provision of incentives for innovation. Ways to strengthen such incentives include the provision of opportunities for trials of innovative vehicles and devices, streamlining the implementation of regulatory revisions that are demonstrated to be beneficial, use of performance standards, and closer linkage of user fees to costs. Construction of exclusive truck roads to eliminate car–truck conflicts may be justifiable under special circumstances. The mixing of cars and trucks in the traffic stream generates costs that would be avoided if the two kinds of vehicles did not share the same roads. In addition to the potential traffic and safety benefits of separation, savings would occur if car-only lanes could have more lightly constructed pavement and bridges. Evaluations of proposals for exclusive facilities should include examination of how user fee policies on exclusive truck roads and on competing unrestricted routes would affect feasibility. Better understanding is needed of the value car travelers would place on access to truck-free roads. The application of information technology to enforcement has made a promising start, but substantial development work is needed before this technology can achieve its full potential for improving enforcement efficiency and facilitating the enforcement of permit operations. The immediate priorities are as follows: Development of databases and information systems needed to give enforcement officials access to the full enforcement history and credentials of vehicles, drivers, and carriers;

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 Expansion of established automated clearance systems by enhancing the value of the systems to industry and the states; and Planning and pilot studies of new technologies and applications, such as permit enforcement systems, repeat offender tracking and monitoring, self-enforcement, and GPS applications. Because evaluation and monitoring of enforcement are lacking, the magnitude of the compliance problem and the effectiveness of alternative enforcement strategies are unknown. Information technology is a valuable enforcement tool, but will not by itself overcome institutional and political obstacles to effective enforcement of truck regulations. The reviews in this chapter of mitigation and enforcement proposals have consistently revealed that evaluations essential to progress on reducing the costs of truck traffic have not been performed. In summary, these evaluations include the following: Measurement of the relationships between truck handling and stability properties (for example, rollover threshold) and accident risk; Examination of whether essential trade-offs exist between safety costs and other truck operating costs per unit of freight services (for example, trade-offs between safety and cargo-carrying capacity); Development of certification and monitoring procedures that would provide the opportunity for innovative vehicles to be demonstrated and evaluated; Measurement of the relationship of vehicle characteristics other than static axle weights and spacing, in particular suspension and tire properties, to pavement and bridge costs; Measurement of the relationship of size and weight law enforcement and size and weight violations to accident risk; Monitoring of rates of violation of size and weight regulations by road class, type of trucking operation, and other characteristics that would allow enforcement to be effectively targeted; Evaluation of alternative enforcement strategies, including applications of information technology for vehicle identification and automated enforcement, through planning studies and pilot implementations. Because all these topics are closely related to the effectiveness of size and weight regulations and to the capability of the federal government and state highway agencies to control the costs of truck traffic, conducting the evaluations would be suitable tasks for the independent

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 Commercial Traffic Effects Institute proposed in Chapter 3. The scope of the list of unfulfilled information requirements is an indication of the value such an Institute could have if it were well supported in federal law and by the interested parties. Some of the topics on this list are related to established functions of existing federal agencies; these evaluations could be conducted through cooperative arrangements overseen by the Secretary of Transportation and involving the Institute and the responsible DOT agency. REFERENCES Abbreviations ARRB Australian Road Research Board ATA American Trucking Associations DOT U.S. Department of Transportation FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration LTSS North American Free Trade Agreement Land Transportation Standards Subcommittee NCHRP National Cooperative Highway Research Program NJDOT New Jersey Department of Transportation NRTC National Road Transport Commission OIG Office of the Inspector General, U.S. Department of Transportation RTAC Roads and Transportation Association of Canada SCAG Southern California Association of Governments TRB Transportation Research Board TXDOT Texas Department of Transportation VDOT Virginia Department of Transportation ARRB. 2000. Specification of Performance Standards and Performance of the Heavy Vehicle Fleet: Discussion Paper. National Road Transport Commission, Melbourne, Australia, Aug. ATA. 2001. Transport Topics; Supplement. Bureau of the Census. 1995. 1992 Census of Transportation: Truck Inventory and Use Survey: United States. May. Bureau of the Census. 1999. 1997 Economic Census: Vehicle Inventory and Use Survey: United States. Oct. Cullen, D. 1999. Smart Brakes: Electronic Braking Systems Will Soon Be Fact, Not Fantasy. Fleet Owner, Aug., pp. 58–62. DOT. n.d. IVI Generation 0 Field Operational Test Program. www.its.dot.gov/ivi/ivifot.html. DOT. 2000. Comprehensive Truck Size and Weight Study. Aug. Ervin, R. D., and A. Mathew. 1988. Reducing the Risk of Spillage in the Transportation of Chemical Wastes by Truck. UMTRI.

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 FHWA. 1993. Overweight Vehicles—Permits and Penalties. Cited in Titus, M. J. Benefits of Electronic Clearance for Enforcement of Motor Carrier Regulations. In Transportation Research Record 1522, TRB, National Research Council, Washington, D.C., pp. 64–68. FMCSA. n.d. Safety and Fitness Electronic Records System. www.safersys.org. FMCSA. 2000. Commercial Vehicle Information Systems and Networks. U.S. DOT, Washington, D.C. www.jhuapl.edu/cvisn. Gillespie, T. D., S. M. Karamihas, M. W. Sayers, M. A. Nasim, W. Hansen, N. Ehsan, and D. Cebon. 1993. NCHRP Report 353: Effects of Heavy-Vehicle Characteristics on Pavement Response and Performance. TRB, National Research Council, Washington, D.C. Grenzeback, L. R., J. R. Stowers, and A. B. Boghani. 1988. NCHRP Report 303: Feasibility of a National Heavy-Vehicle Monitoring System. TRB, National Research Council, Washington, D.C. Hajek, J. J., and O. I. Selsneva. 2000. Estimating Cumulative Traffic Loads, Final Report for Phase 1. FHWA, July. Jasek, D., M. A. Shafer, D. L. Picha, and T. Urbanik II. 1997. Guidelines for Truck Lane Restrictions in Texas. Research Report 1726-S, Texas Transportation Institute. Klingenberg, B., G. Rossow, and R. Jacobson. 1989. FACT—The Freightliner/ Heil Advanced Concept Truck. SAE Technical Paper Series 892462. Land Transport Safety Authority. 2001. Truck Stability Scrutinized. Road Safety New Zealand, Aug. www.ltsa.govt.nz/publications/rsnz. LTSS. 1999. Highway Safety Performance Criteria in Support of Vehicle Weight and Dimension Regulations: Candidate Criteria & Recommended Thresholds. Working Draft, Nov. March, J. W. 2001. DOT’s Comprehensive Truck Size and Weight Study. Public Roads, Vol. 64, No. 5, March–April, pp. 2–9. Monson, S. H. 1990. Statement of Stephen H. Monson on Enforcement. In Special Report 225: Truck Weight Limits: Issues and Options, TRB, National Research Council, Washington, D.C. Moore, T. 1998. Fleet Managers Figure It Out: New Holistic Approach to Driver Retention . Fleet Owner, April. Mueller, T. H., J. J. De Pont, and P. H. Baas. 1999. Heavy Vehicle Stability Versus Crash Rates. New Zealand Land Transport Safety Authority, July 9. NCHRP. 1998. NCHRP Research Results Digest 229: Developing Measures of Effectiveness for Truck Weight Enforcement Activities. TRB, National Research Council, Washington, D.C. NJDOT. 2000. NJ Transportation Fact Book 2000: Goods Movement. www.state.nj.us/transportation/publicat/Facts/goods.htm, Sept. 6. NRTC. n.d. National Heavy Vehicle Dimensions, Mass Limits & Registration Charges. www.nrtc.gov.au/place/index.asp. NRTC. 1999. Alternative Compliance (Heavy Vehicle Accreditation Scheme): Information Bulletin. Melbourne, Australia, April.

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 NRTC. 2000a. 2000 Annual Report. Melbourne, Australia, Sept. 29. NRTC. 2000b. Compliance Outcomes (Smart Compliance): Information Bulletin. Melbourne, Australia, March. OIG. 1991. Report on the Audit of the Vehicle Weight Enforcement Program. U.S. Department of Transportation, Washington, D.C., Nov. 21. PrePass. n.d. PrePass, A Nationwide Weigh Station Bypass Service. www.prepass.com. RTAC. 1986. Vehicle Weights and Dimensions Study: Technical Steering Committee Report. Ottawa, Canroad Transportation Research Corporation, Dec. RTAC. 1988. The Memorandum of Understanding on Interprovincial Vehicle Weights and Dimensions: Summary Information. Feb. SCAG. 2000. Truck Lane Feasibility Study, Task Report, Task 5, Conceptual Designs: Operational Assessments and Financial Analysis. June. Sharp, K. G., P. F. Sweatman, and R. R. Addis. 1998. OECD Cooperative International Research into Vehicle-Road Interaction—DIVINE Project. Road & Transport Research, Vol. 7, No. 1, March, pp. 48–55. Skalny, P. 2001. 21st Century Truck Initiative: Developing Technologies for 21st Century Trucks. U.S. Army Tank-Automotive and Armaments Command, tacom.army.mil/tardec/nac/21ctruck/cong329.htm, June 29. Small, K., C. Winston, and C. Evans. 1989. Road Work: A New Highway Pricing and Investment Policy. Washington, D.C., Brookings. Stevenson, J. 1999. Performance Standards and Transport Reform. Presentation at ICM Intermodal Logistics Conference, National Road Transport Commission, Nov. 4. TRB. 1986. Twin Trailer Trucks. National Research Council, Washington, D.C. TRB. 1989. Special Report 223: Providing Access for Large Trucks. National Research Council, Washington, D.C. TRB. 1990a. Special Report 225: Truck Weight Limits: Issues and Options. National Research Council, Washington, D.C. TRB. 1990b. Special Report 227: New Trucks for Greater Productivity and Less Road Wear: An Evaluation of the Turner Proposal. National Research Council, Washington, D.C. Trowbridge, A., D. Nam, F. L. Mannering, and J. Carson. 1996. The Potential for Freight Productivity Improvements Along Urban Corridors. Report WA-RD 415.1, Washington State Department of Transportation, Dec. TXDOT. 1999. I-35 Trade Corridor Study-Recommended Corridor Investment Strategies. I-35 Steering Committee, Sept. 30. VDOT. 1999a. Route 81 Traffic Data. Oct. 4. VDOT. 1999b. I-81 Update. Spring. Weatherly, B. 1988. Steady as She Goes. Commercial Motor, June 2–8, pp. 50–51.

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 Whitten, D. L. 2001. Trucking Research Hampered by Fund Cuts, But U.S. Agencies, Industry Continue Efforts. Transport Topics, Aug. 27, pp. 14–15. Winkler, C. 2000. Rollover of Heavy Commercial Vehicles. UMTRI Research Review, Oct.–Dec., pp. 1–17. York, J., and T. H. Maze. 1996. Applicability of Performance-Based Standards for U.S. Truck Size and Weight Regulations. 1996 Semisesquicentennial Transportation Conference Proceedings, Center for Transportation Research and Education, Iowa State University.