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.
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.
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
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.
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
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
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-
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:
Access (i.e., compatibility with the roadway and with other traffic),
Truck freight productivity, and
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.
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
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
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.
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
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.
Advisory Systems Three diverse systems for providing timely information intended to reduce accident losses are being evaluated. The Trucker Safety Advisory system warns the driver when the truck approaches a location that historically has experienced frequent heavy-vehicle crashes. The Lane Departure Warning system observes the driver’s performance in keeping the truck within the lane and warns the driver if the truck strays near or over the lane edge. The Automatic Collision Notification system detects the occurrence of a crash and sends a message identifying the truck and its location to a dispatcher or other agent of the carrier that operates the vehicle. The system is intended as an aid to emergency response. Thirty-six trucks are to be equipped with the devices for the trial. Participants include a truck manufacturer, the companies that developed the safety devices, and a carrier.
Other Truck Technology Programs
Two other programs in the United States are aimed at making systematic improvements in large-truck performance, including safety. The federal 21st Century Truck Initiative originated as a program of the U.S. Army to reduce acquisition and operating costs and improve the safety of military trucks, but was expanded to involve civilian agencies, including the Department of Energy and DOT (Skalny 2001). Future funding for this program is reported to be uncertain (Whitten 2001). The American Trucking Associations’ Future Truck Program, in operation since 1984, is an industry effort to communicate the needs of carriers to truck and equipment manufacturers, set priorities for product development, and facilitate trials and demonstrations. The program’s focuses have included cab design, engine durability, and brake performance (Whitten 2001).
Mitigation of Highway Costs Through Vehicle Design
Truck design improvements can reduce infrastructure costs as well as safety hazards. The characteristics of truck suspensions and tires affect pavement and bridge wear. Increasing tire pressure or substituting single tires for dual tires on truck axles will accelerate some forms of pavement wear. Suspension and tire attributes influence the dynamic loads to which pavements and bridges are exposed, that is, the magnitude and frequency of peak forces that occur as a vehicle travels over a road. The distribution of load among the axles in a tandem- or tridem-axle group also depends on the suspension. Maintaining even load distribution tends to reduce pavement wear. Study of these relationships has
been an active area of research in the United States and internationally. The goals have been to understand how the dynamic characteristics of loads affect pavement and bridge wear and to test whether changes in vehicle suspension and tire designs can reduce infrastructure costs (Gillespie et al. 1993; Sharp et al. 1998).
As a result of research findings linking the dynamic characteristics of loads to pavement wear, at least 11 jurisdictions outside the United States allow greater maximum weights for vehicles equipped with air suspension, which is regarded as the most road-friendly design, or with suspension meeting other criteria related to dynamic loading characteristics (York and Maze 1996). These regulations have been viewed as prototypes of the performance standards approach to truck regulation. An alternative form of incentive would be to charge lower highway user fees to trucks equipped with suspensions and tires of designs that demonstrably cause less road wear.
The benefits of road-friendly suspension are not well established. They will depend on maintenance and enforcement, as well as on the performance of new vehicles and on careful specification of performance standards. The TRB Turner Proposal study estimates that improved suspensions could reduce the cost of pavement wear by about 5 percent (TRB 1990b, 176). The maximum gross weight allowances for road-friendly suspensions recently enacted in Australia range from 3 to 9 percent for combination vehicles with five or more axles, suggesting that authorities there may be expecting a reduction in pavement wear somewhat greater than that estimated in the TRB study (NRTC n.d.).
SEPARATION OF CAR AND TRUCK TRAFFIC
Size and weight regulation is an aspect of the problem of provision of adequate freight system capacity. Trends in the growth of freight demand, especially in certain high-density corridors, imply that substantial expansion of truck capacity, as well as improved capacity management, will be required to maintain present service levels. Exclusive truck facilities have been proposed as one design option for future additions to capacity.
Constructing dual facilities would require duplication of some features, adding to costs. The quantities of median strips, shoulders, and interchange ramps would increase. In most designs that have been proposed, it is assumed that the minimum size for the truck-only facility is two lanes in each direction to allow for safe passing. Under this assumption, separating traffic on a four-lane highway would require
construction of four additional lanes, although in a road network, it might be possible to close more than 1 mile of highway to trucks for every mile of truck-only lanes built. In operation, separation of traffic causes the loss of some economies; in particular, a lane strictly dedicated to one vehicle type that happens to be uncongested cannot be used by other vehicle types.
Offsetting these costs would be possible savings from two sources. First, mixing traffic affects road construction and operating costs. An expressway carrying 200,000 cars a day and no large trucks would cost appreciably less to build than one carrying 190,000 cars and 10,000 large trucks because truck characteristics determine requirements for pavement durability, bridge strength, specifications for guardrail and other safety appurtenances, and horizontal and vertical alignments. According to one estimate, nearly a quarter of the cost of building a typical urban expressway would be saved if the road were restricted to automobiles (Small et al. 1989, 111). If trucks could be restricted to two lanes on a new eight-lane expressway, the cost of constructing pavement and bridges for the six car lanes would be lower than if the lanes had to carry trucks, and the pavement and bridge construction costs of the two truck lanes would be no greater than those for building two mixed-traffic lanes. One consideration in evaluating such a proposal would be the practicality of excluding trucks from the car lanes for all purposes, including maintenance and emergencies.
The second and perhaps more significant source of savings would be a reduction in traffic conflicts. Cars and trucks differ greatly in dimensions, weight, acceleration, speed, braking distance, sight distance requirements, and driver skills. Mixing these very different vehicles creates operational problems and hazards that would not exist in a traffic stream of uniform vehicles. A high volume of truck traffic appears to be a source of stress and anxiety for car drivers. On urban expressways, accidents involving large trucks sometimes cause widespread and protracted delay. Therefore, separation of cars and trucks might mitigate the impacts of truck traffic by reducing accident losses, congestion, and nuisance to car travelers.
Segregation of traffic according to vehicle size can take several forms, including provision of lanes reserved exclusively for trucks, exclusive car lanes, or rules barring the largest trucks from all but a restricted network of the highest-quality roads. All of these arrangements are in use and have been subject to evaluation, although experience and information on their impacts are still limited. The restriction of larger trucks to designated networks is evaluated in the past DOT
and TRB truck size and weight studies, and a TRB policy study committee has considered the problem of providing access for large trucks from a designated network to final destinations (TRB 1989). The remainder of this section describes evaluations of exclusive truck facilities.
There has been virtually no experience with exclusive truck facilities in the United States or internationally. Apparently, the only such facility in operation in the United States in 1997 was a segment of Interstate 5 near Los Angeles, where a reconstruction project created two separate roadways through three major interchanges. The truck lanes bypassed the intersections. A few other roads have lanes designed primarily to serve trucks but allow cars as well (Jasek et al. 1997, 12–13). One substantial exclusive facility is in development in the United States; as part of its Portway project, New Jersey is planning to construct a truck-only tolled highway connecting the Newark– Elizabeth air and seaport complex to the region’s main highways (NJDOT 2000).
A number of prospective evaluations of exclusive truck lanes at particular sites have been conducted. In Virginia, the state is planning to widen Interstate 81 in stages over a period of 20 years to accommodate expected traffic growth. I-81, running from Tennessee to New York, is a major eastern U.S. truck route (VDOT 1999a; VDOT 1999b). The state studied construction of exclusive truck lanes as part of the project. The Virginia Department of Transportation’s analysis, conducted at the direction of the state legislature, questioned whether a separate facility would be justifiable, although the state is still considering the option. The design considered was for two truck-only lanes in each direction (because provision for passing would be essential) and separate truck lanes on some interchanges. The facility would have required more right-of-way acquisition than widening following a conventional design, increasing the potential for environmental damage and community disruption. Most important, if a separate truck facility were constructed and automobiles were left with the four lanes of the present highway, automobile travelers would still experience significantly degraded levels of service by 2020. That is, the truck-only lanes would not solve the underlying problem. Finally, it was concluded that the recommended design would be safer than the separate truck facility option. The analysis apparently did not include estimation of cost savings from not having to accommodate large trucks in the automobile-only lanes or any service improvements perceived by car travelers as a result of the absence of trucks, other than reduced congestion delay.
The states have recently undertaken several detailed planning studies of regional freight and passenger corridors. These studies have considered special provisions for trucks, but no firm plan for an exclusive interstate truck facility has emerged. An example is the I-35 Trade Corridor Study, which considered future development of the interstate corridor from Laredo, Texas, to Duluth, Minnesota. Further evaluation of special truck features for the most heavily traveled segment of the route was recommended, including provisions for trucks larger than current limits and truck-only lanes (TXDOT 1999).
The Southern California Association of Governments has evaluated a proposal to develop exclusive truck lanes with tolls on 37 miles of US 60 (the Pomona Freeway) in Los Angeles. The proposed design is for two lanes in each direction. A market analysis revealed that truck tolls could finance only 20 percent of the cost of constructing the truck lanes. The limit on toll revenue is competition from free roads. Most trucks are predicted to divert from the toll facility at higher toll rates (SCAG 2000). As in the Virginia I-81 study, the traffic projections indicate that if exclusive truck facilities were constructed, the adjacent car lanes would be highly congested in the forecast year of 2020. Therefore, as in Virginia, the most beneficial use of the lanes once built might be to open them to all vehicles instead of restricting them to trucks. These two studies suggest that if building truck-only lanes precludes expanding car capacity on a route, the truck-only lanes will be difficult to justify unless trucks represent a very large share of total traffic, or car travelers place a high value on truck-free traffic as an amenity.
A Washington State study produced results somewhat more favorable to traffic separation. The proposal evaluated was for trucks and buses to use existing high-occupancy vehicle (HOV) lanes in the Puget Sound region, along with high-occupancy cars. This strategy was projected to save travel time for trucks and to decrease the variability of truck trip times. The major beneficiaries in the projections were low-occupancy autos, which would save travel time because of the removal of trucks and buses from the general traffic stream. The option of designating or constructing exclusive truck lanes was estimated to have no greater benefits and much higher costs (Trowbridge et al. 1996).
The limited results of past analyses, together with evidence from the projects that are being pursued most seriously (that is, those in Southern California and New Jersey), tend to support the conclusion that exclusive truck facilities would most likely be justifiable on very-high-volume routes within urban areas rather than on long intercity
routes. Yet certain factors not adequately considered in past evaluations may have a large influence on whether exclusive facilities appear attractive. For example, no study has considered the possibility that car occupants using truck-free lanes would derive benefits beyond conventionally defined user cost savings in the form of reduced discomfort or stress. Few studies have considered the possibility of cost savings from lighter construction of bridges, pavements, and other road features on car-only lanes, and most studies have not considered how finance arrangements, in particular the use of tolls on exclusive facilities and on competing routes, would affect feasibility.
The federal government is not directly engaged in enforcing size and weight limits. Rather, federal truck size and weight laws include provisions imposing requirements on the states for enforcement of weight regulations. State enforcement of size and weight laws traditionally has concentrated on checking gross vehicle weights and axle weights at fixed stations and with portable scales. Enforcement of dimensional limits was complicated by the 1983 revisions to the federal regulations, which required the states to allow, on a limited network of major roads, semitrailers that were longer and wider than the dimensions then common. In many jurisdictions, the problem of enforcing this federal rule has diminished with time as the larger trailers have become accepted on most roads. Enforcement of special permits, which allow operation of vehicles larger and heavier than the statutory maximums and often specify route restrictions, presents special challenges.
This section addresses only enforcement of size and weight regulations. However, other areas of legal enforcement are relevant to the control of truck costs and to the effectiveness of size and weight regulation. These include enforcement of tax payment, carrier qualifications, vehicle standards regarding safety and pollution control, and driver qualifications.
As noted in the introduction to this chapter, enforcement has a large effect on the cost of truck transportation because the heaviest loads (which may include illegal overloads and trucks operating with legal permits) account for a disproportionate share of infrastructure costs attributable to trucks. It is generally believed that effective enforcement of size and weight laws can reduce truck accident losses, although this benefit has not been not established empirically. Therefore, enforcement is an important consideration in evaluating proposals for reform
of size and weight regulations. If enforcement is lax in general, reforms are less likely to produce the intended results. Furthermore, changing the regulations may affect the frequency and severity of violations. For example, new regulations might be more difficult to enforce because of complexity or might promote use of trucks with characteristics that make them easier to overload.
When evaluation and oversight are insufficient, proliferation of permit operations, grandfather exceptions, and other special exceptions for trucks with dimensions exceeding nominal limits has consequences similar to those of lax enforcement. Although data are incomplete, the incidence of permit operations and exceptions appears to be growing nationwide. It is important for legislators and policy makers planning reforms to recognize that the statutory limits do not dictate truck dimensions. Rather, they interact with many other factors to influence the diversity of the dimensions of trucks commonly operated in the United States today.
The extent and costs of overweight/oversize operation are first described below. Proposals from past evaluations for improvements in enforcement practice are then summarized. Finally, some emerging new approaches, including applications of information technology that have the potential to revolutionize enforcement in the future, are reviewed.
Extent of Oversize/Overweight Operations and Enforcement Effectiveness
Data on the actual weights of trucks in use are fragmentary and inconsistent. A meaningful estimate would require surreptitious weighing and an appropriate sample design for selection of vehicles or weighing sites. Large-scale studies meeting these requirements have not been carried out. The following subsections summarize the available information on the extent of illegal overloads, the scope of permit operations, the cost of overweight/oversize operations, and the effectiveness of enforcement.
A 1988 National Cooperative Highway Research Program study synthesized available truck weight data. The study yielded a “conservative” estimate that 15 percent of large trucks would exceed axle weight or gross vehicle weight limits on a segment of Interstate highway where enforcement was not taking place and that the minimum rate of violations would be 6 percent (the frequency of axle weight violations at fixed scales in the data examined for the study) (Grenzeback et al.
1988, 23). Only 0.6 percent of trucks exceed gross vehicle weight limits at weigh stations (FHWA 1993), but overweight trucks routinely avoid the stations.
Installation of automatic weigh-in-motion (WIM) devices in recent years has provided some new information about the frequency of overloads, although uncertainties are introduced in converting the devices’ readings to equivalent static load distributions, and data collection and analysis have not been designed for the purpose of assessing compliance with weight regulations. In WIM data from several hundred sites on all road systems in 18 states collected for the DOT Long-Term Pavement Performance program, roughly 12 percent of tandem axles exceeded 34,000 lb (the federal maximum) (Hajek and Selsneva 2000, Figure 11). This rate for all trucks (loaded and unloaded) implies a rate for loaded trucks of 15 percent of tandem axles exceeding the federal maximum. An appreciable share of the trucks exceeding the federal limit in these data would be operating legally under higher state limits or permits.
Unpublished DOT estimates, compiled from various sources, attribute 10 percent of all miles of travel by trucks with three or more axles to vehicles weighing more than 80,000 lb (the federal Interstate highway weight limit), including both legal and illegal operations. This estimate appears roughly consistent with the rate of overloaded axles from WIM data cited above. It should be recognized that the majority of large trucks on the road at any given time weigh less than the legal maximum. Trucks under the weight limit include those that are partially loaded or empty and those carrying low-density commodities.
State officials perceive the problem of illegal overloads to be concentrated in certain segments of the trucking industry. Vehicles carrying dense bulk commodities (for example, agricultural and mining products and construction materials) usually are constrained by the weight limits and therefore have a strong economic incentive to exceed them. Compared with all truck traffic, these trucks tend to be found more often on secondary roads traveling short distances and to be operated by local businesses. This segment also appears most likely to be favored with special legislative exemptions. Other categories of truck operations, such as van trailers operated by Interstate carriers hauling merchandise over long distances on main roads, are regarded as less likely violators. These trucks often are not constrained by the weight limits because their cargo is of low density, and their routes are subject to the most intense enforcement. A lack of data makes such generalizations difficult to verify, however.
Grandfather and Permit Operations
According to DOT tabulations, four states have grandfathered statutory gross weight limits over 80,000 lb on the Interstates (DOT 2000, Vol. II, II-13–II-14). In addition, an unpublished DOT tabulation shows that 27 states exercise grandfather rights (or possibly other special legislative exemptions) to issue divisible-load permits for vehicles over 80,000 lb on the Interstates. Divisible loads are cargoes that could practicably be divided and carried in more than one vehicle, such as bulk commodities or goods loaded on pallets. (Under federal law, states may issue permits allowing trucks carrying nondivisible loads, such as structural members or heavy equipment, to exceed federal weight limits on the Interstates.) Of these 27 states, 5 issue the permits only on toll road sections of the Interstates, and 5 others issue permits on other limited segments of their Interstates. Of the states allowing trucks over 80,000 lb on the Interstates, 12 are east of the Mississippi. An industry tabulation (ATA 2001) shows four more states than appear on the FHWA list with weight limits over 80,000 lb.
Since enactment of the federal Interstate weight limits, federal law has exempted certain roads and kinds of truck operations. TEA-21 [Section 1212(d)] contains special provisions for trucks hauling concrete panels in Colorado and sugar cane in Louisiana and for exemption of specified Interstate highway segments in Maine and New Hampshire from federal weight limits. Congress enacted other special provisions in the National Highway System Designation Act of 1995 (P.L. 104-49, Sec. 312) exempting specified highways in Iowa and Wisconsin from certain federal limits.
Most of the states holding grandfather rights and other exceptions use them extensively. According to DOT data, 212,000 multiple-trip divisible-load permits were issued in the United States in 1995. Nearly 90 percent of these permits were issued in states with grandfather rights to allow overweight trucks on the Interstates. According to DOT, “multitrip permits essentially allow unlimited operation with no accounting for mileage or routes for a greater length of time, generally one year” (DOT 2000, Vol. II, II-19–II-20).
Multiple-trip divisible-load permitting has been growing rapidly. According to FHWA surveys of the states, the number of such permits issued annually increased 180 percent between 1983 and 1995, from 54,000 to 212,000 (DOT 2000, Vol. II, II-21). No data are collected on miles traveled by trucks operating under these permits.
Sixteen states have statutory gross vehicle weight limits greater than 80,000 lb for highways other than the Interstates. Four additional
states that do not have grandfather rights to operate trucks over 80,000 lb on the Interstates issue substantial numbers of divisible-load permits, presumably for operation of heavier trucks on other roads. Double-trailer combinations with twin 28-ft trailers and gross weight of up to 80,000 lb operate legally in every state by federal law. In addition, 22 states allow operation of longer and heavier multitrailer combinations (DOT 2000, Vol. II, II-13–II-14, II-21, II-19).
Representative nationwide data do not exist on the frequency of legal loads (i.e., trucks operating under higher state limits or permits) over 80,000 lb gross vehicle weight. In the 1997 Vehicle Inventory and Use Survey (U.S. Bureau of the Census 1999, Table 10), vehicles that reported operating with an average loaded weight of more than 80,000 lb accounted for 3.3 percent of all combination VMT. Since these weights were self-reported, this fraction may indicate the extent of legal loads over 80,000 lb. In the 1992 survey, this share was 2.9 percent (U.S. Bureau of the Census 1995, Table 13).
Costs of Overweight/Oversize Operations
Since the extent of overweight and oversize truck operations on U.S. roads is poorly known, only rough estimates can be made of the costs of these operations (compared with the costs of truck operations and highways if all vehicles complied with statutory limits). According to the TRB Truck Weight Limits study, if all illegally overweight axle loads were eliminated and the volume of truck freight carried remained unchanged, highway agency pavement costs would decrease by $160 million to $670 million annually (TRB 1990a, 254–255). This range reflects uncertainty over the rate of violations. At today’s prices and traffic volumes, the savings would be somewhat greater. The study does not estimate bridge cost savings or the effect on shippers’ costs of eliminating illegal overloads. Under the assumption that the quantity of truck freight would be unchanged, and using other assumptions consistent with those in the Truck Weight Limits study, rigorous enforcement would cause an increase in annual VMT by large trucks of 0.5 to 2.5 percent, at a cost to shippers of $500 million to $2.5 billion annually. In other words, shippers might prefer to pay the added pavement costs generated by their overloaded trucks instead of reducing their loads.
Truck Weight Limits and the DOT (2000) Comprehensive Truck Size and Weight Study estimate the effects of eliminating the states’ exemptions from federal limits as provided for by the grandfather clauses in the federal size and weight laws. Both studies conclude that
the cost of lost productivity in truck freight transportation would be greater than the savings in highway agency costs. (TRB 1990a, 158; DOT 2000, Vol. III, V-14, VI-12, IX-9, XII-4). The uncertainties in these studies’ projections of freight traffic and infrastructure costs are described in Chapter 2. If the studies underestimate the responsiveness of the demand for truck transportation to changes in costs, then they overestimate the cost in lost productivity of elimination of grandfather rights. However, their estimates do suggest that the larger trucks operating under grandfather exemptions would be willing to pay user fees adequate to cover additional costs to highway agencies in return for the privilege of continuing operation.
Effectiveness of State Enforcement Programs
Few evaluations have been performed of the relationship between the level of effort or strategy of state enforcement and the rate of size and weight violations. A 1998 review for NCHRP led to the following conclusion:
Wide divergence in enforcement practice across that United States confounds the problem of assessing [compliance] trends. It is impossible to gauge the impact of enforcement activity without a systematic data-sampling approach…. At present, the effects of truck weight enforcement programs are generally not known in terms of (1) actual impact on weight-law compliance, (2) effect on safety of truck operations, (3) pavement service life effects, or (4) cost-effectiveness of enforcement activity. (NCHRP 1998, 2)
FHWA is responsible for certifying that states are complying with the federal requirement that they enforce weight limits on the Interstates. In 1991 the DOT Office of Inspector General (OIG) evaluated FHWA’s oversight on the basis of investigations of a sample of eight states. OIG concluded that a lack of data was preventing FHWA from assessing the effectiveness of state weight enforcement programs (OIG 1991). A need was identified for the development of automatic weight monitoring systems and statistically valid sampling plans for use in determining actual distributions of weights and changes over time. Other findings highlighted in the OIG report include an imbalance between enforcement effort on the Interstates and on other highways and the problem of repeat violators. None of the eight states audited imposed progressively higher fines for repeated violations.
Proposals for Reform of Size and Weight Enforcement
Both the 1991 OIG report and the 1990 Truck Weight Limits study propose enforcement reforms that are similar on essential points. The same reform principles underlie the enforcement program being developed by Australia’s NRTC. These three proposals are summarized below. All three call for institutional or procedural reforms with three goals: strengthening incentives for compliance (for example, by imposing higher fines and by holding shippers accountable); targeting enforcement efforts (e.g., at repeat offenders and on roads with high violation rates); and developing information systems to monitor compliance, evaluate effectiveness, and direct resources.
Office of Inspector General Report
The OIG recommendations are for changes in FHWA oversight, but would have a profound effect on state practices if implemented. It is recommended that FHWA undertake the following measures (OIG 1991, 23):
Develop a program to produce the data needed to quantify the extent of overweight traffic, for use in state enforcement and federal oversight.
Require that the states formulate annual enforcement plans based on valid monitoring data and that they demonstrate the effect of enforcement on violations in order to receive certification of their enforcement programs.
Develop standards and technological improvements for automatic WIM systems used to monitor weights and compliance.
Request Congress to restrict state use of divisible-load permits and multiple-trip nondivisible load permits on the Interstate system.
Work with the states to evaluate fine structures and demonstrate that they deter violations.
Promote nontraditional enforcement techniques, including the Relevant Evidence Audit Program introduced in Minnesota. Under this program (Monson 1990, 275; DOT 2000, Vol. II, VII-12), the state legislature gave state enforcement officials authority to inspect the terminals and offices of shippers and receivers for evidence that illegal loads had been dispatched or received.
In 1993, in response to the OIG recommendations, FHWA published a proposal to revise its oversight functions. Action on these reg-
ulatory revisions was postponed, and the proposal was republished in 2000.
Truck Weight Limits Study
Truck Weight Limits diagnoses the states’ poor enforcement record as primarily an institutional problem. Political pressures frequently work against vigorous enforcement when local industries and agriculture are the likely targets, and police and judges often are ignorant of the need for the regulations and the consequences of violations. Generally the defendant in adjudication is the truck driver, but decision-making power regarding loading rests with the carrier or the shipper (TRB 1990a, 135–143).
As a component of the permit program proposed in the study, a portion of the revenues from fees paid by carriers for permits would be dedicated to increasing the resources devoted to enforcement; the level of enforcement effort would be increased, especially on roads other than Interstates; and greater use would be made of portable scales and of WIM installations for screening trucks to increase enforcement efficiency. The study also recommends that fines be increased. It is estimated that in a typical case, the cost savings to a carrier from operating overweight would be several times the carrier’s expected liability for fines (p. 140). In fact, the appropriate fine to protect the public from loss would be equal to the added cost for infrastructure wear caused by the overload divided by the probability that a violator will be caught.
The Truck Weight Limits study committee recommended that Congress consider the following measures to strengthen enforcement:
Direct federal funding of state enforcement, possibly by amending the federal Motor Carrier Safety Assistance Program, which provides funding to states for enforcement of federal truck safety regulations;
Imposition of federal penalties for violations of federal weight limits on Interstate highways, or alternatively, mandating of minimum state penalties;
Federal provision for assessing penalties against the parties responsible for placing overweight shipments into commerce, that is, enforcement targeted at shippers as well as carriers and drivers;
Federal support for state measures to place overweight trucks out of service until they are offloaded;
Development of educational programs for judges and prosecutors regarding the overweight problem; and
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.
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.
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,
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
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.
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.
Promising new techniques for reducing the costs of truck travel, including safety costs, are becoming available. If these techniques prove
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;
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
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.
Australian Road Research Board
American Trucking Associations
U.S. Department of Transportation
Federal Highway Administration
Federal Motor Carrier Safety Administration
North American Free Trade Agreement Land Transportation Standards Subcommittee
National Cooperative Highway Research Program
New Jersey Department of Transportation
National Road Transport Commission
Office of the Inspector General, U.S. Department of Transportation
Roads and Transportation Association of Canada
Southern California Association of Governments
Transportation Research Board
Texas Department of Transportation
Virginia Department of Transportation
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