Introduction

It has often been said that highway engineers design trucks through the weights and dimensions regulated by Road Use Laws. These Laws, promulgated by the highway community through the political process, fix the loads and their distribution on truck axles and the locations of the axles, as well as the overall dimensions of the vehicle or vehicle combination. While the vehicle owner has some latitude in tailoring the vehicle to its intended mission, and to achievement of maximum productivity, the vehicle must be designed to Road Use formulae intended by law to preserve the infrastructure.

The historical base for this observation extends back to the beginning of the highway system [1]. The focus on the interaction between cargo vehicles and road and bridge structures is documented in the book, Ways of the World [2] by Max Lay, which cites a number of efforts over the centuries to achieve reasonable balance between protecting the roadway and efficient transport. Among the interesting facts he cites are:

1) The earliest recorded vehicle load limits date from 50 BC when Romans restricted loads to about 250 kg.

2) Although load limits increased with time the Roman Theodosian Code of 480 AD limited the number of animals (horsepower) that could be used to pull the vehicle as a means to limit loads.

3) A 1662 regulation in England set minimum wheel widths at 100 mm.

4) By the late 1700s English regulations allowed any number of horses if the wagon wheels were at least 400 mm wide.

Today commercial transport has evolved to the use of pneumatic-tired trucks with tires of approximately 300-400 mm width, carrying 2.5-4.5 tonnes each.

The spirit of Simultaneous Vehicle Infrastructure Design calls for communication between the highway community and the community of designers and users of trucks. A number of steps have already been taken in that direction. First among these were the "Highway/Commercial Vehicle Interface Coordinating Task Force" meetings in 1992 in which representatives of truck manufacturers, state departments of transportation, and other transportation industry groups, academics, and federal officials from the Federal Highway Administration (FHWA) and the National Highway Traffic Safety Administration (NHTSA) met to explore means to enhance communication between these groups. While this initiative did not develop further, it set the stage for the FHWA Study Tour for Highway/ Commercial Vehicle Interaction in 1995. The so-called "Scanning Tour" brought together an international cadre of highway and trucking interests to identify options and issues in highway/commercial vehicle interaction technology. The results of that Tour, published in an FHWA Report [3], included a number of recommendations; one of which was to encourage FHWA and AASHTO to provide national leadership "...to address inefficiencies in the nation’s freight transportation system and to promote appropriate solutions." These initiatives set the example for SVID by being bilateral—calling for input from both the highway and trucking interests.

The Federal Highway Administration has underway the Interactive Highway Safety Design Model (IHDSM) program that attempts to provide the highway designer with more of a perspective of the road user during the design process. The goal of the multi-year program is to consider the safety of roadway and roadside design elements in creating cost-effective highway design alternatives. The VDM RoAD Simulation [4] is an example of products from that program that represent a marriage of information and technology from both the highway and vehicle communities. With VDM RoAD the highway designer can feed proposed road design information into a vehicle dynamics model and in that "virtual world" examine how typical vehicles respond to the proposed design as shown in the image below.

Other noteworthy initiatives have been undertaken over the years but these tend to be unilateral in content. Invariably it is the highway community studying trucking and trucking operations to determine how to improve or protect the highway system with only a cursory (or

perhaps—courtesy) involvement from the trucking community. Historically, there have been few initiatives from the trucking community to improve trucking performance or operations requiring participation from highway people. The primary exceptions of late have arisen in the Intelligent Transportation System (ITS) arena—taking the form of cooperative efforts to track and clear trucks in interstate traffic in programs like the Crescent Project, Advantage I75 and others.

The absence of trucking involvement in cooperative endeavors is understandable when we remember that everyone from the truck manufacturers to the operators are in direct competition with each other. For problems of common concern they occasionally come together to seek a solution. In the 1970s and 1980s the Motor Vehicle Manufacturers Association (MVMA) served as the forum primarily for research on such topics as truck ride, handling, braking, splash and spray, and other problems. With the demise of the MVMA, the Society of Automotive Engineers (SAE) has filled the void somewhat, and hopefully the recently established Truck Manufacturers Association (TMA) will join in as well. Typical examples of recent initiatives carried out under this umbrella are studies of heavy truck crashworthiness and test procedures for measuring truck tire traction behavior.

There are many areas of common concern in which the highway and trucking communities could benefit from joint efforts. A recent National Cooperative Highway Research Program (NCHRP) project that examined truck characteristics to identify those that are significant to highway design [5] provides a framework to discuss examples of the areas and the motivations of the interests involved. The topical areas from that study are restructured somewhat in the discussion below.

Pavement and Bridge Life—As pointed out in the opening paragraphs, the relationship between truck characteristics and pavement damage has been of interest since the beginning of public road systems. This matter was approached experimentally over the years, with experiments like the AASHO Road tests [6] conducted in the late 1950s and the recent DIVINE Project [1] attempting to establish empirical relationships between vehicle properties and pavement performance. The same problem has been approached analytically in a recent National Cooperative Highway Research Program (NCHRP) Project [7], from which a more mechanistic understanding of the interactions is obtained.

Although industry participation is sometimes obtained in these programs, it tends to be supportive of the research effort, without evidence that the findings directly affect industry practice. The NCHRP Project suggested practices for truck designers and operators that would reduce road damage by such means as controlling axle loads and tire inflation pressures. However, NCHRP Reports are rarely circulated among that audience. Further, there will be no motivation for operators to observe these practices if they in anyway affect productivity.

An additional observation that came out of the analytical study relates to a potential explanation of the recent problems with rutting of asphalt pavements.

This phenomenon has become serious to highway agencies as "sudden early rutting" has appeared in new asphalt pavements (evident as dual tire tracks). The suggested explanation is the difference in camber properties of radial tires as opposed to bias-ply tires (Radial tires follow in the ruts, whereas the higher camber stiffness of bias-ply tires favors climbing out of the ruts). Radial tires are an improvement in tire technology because of lower rolling resistance, and better cornering and tracking, hence their adoption by truck operators benefits all of society. However, the consequence is creation of a problem for highway engineers that requires development of more rut-resistant asphalt mixes. Whether there is a solution by modifying radial tire characteristics has not been explored.

Intersection Geometrics—Offtracking and swept path dimensions are the metrics relevant to turning performance at intersections. Highway engineers have routinely attempted to take these concerns into account via turning templates for various vehicle combinations [8]. The constant pressure from the trucking industry to allow longer and wider vehicles challenges these standards. Occasionally, rational extensions of policies are made. The pressure to allow 53-foot trailers on public roads reached the State of Michigan in 1985. To aid policy development the Michigan DOT had the University of Michigan Transportation Research Institute (UMTRI) conduct an analysis to determine what areas of performance would be affected and recommend appropriate constraints on operations [9]. Perhaps the most notable fallout from that effort was restriction of the trailer wheelbase on 53-foot trailers (see Fig. 2) to that common with shorter trailers already in use so that maneuverability would not be compromised. A secondary benefit from that study was identification of requirements for rear guards on the trailers in order to prevent under-ride accidents with the larger trailer overhang caused by the wheelbase restriction.

As in many cases, the collaboration involved in this effort was between government and academia, without direct industry input. The industry interest was to obtain access to longer trailers. Their efforts were directed at the political level, such that they were only observers of the study conducted by UMTRI. On the other hand, one could seriously question whether they should have been participants in the study for fear that the objectivity would be hard to maintain with industry participation.

Vision and Sight Distance—Truck operations on highways are affected by the low performance of these vehicles and the differences in driver position that relate to vision issues, particularly for the truck driver. Traffic flow and safety at intersections can be compromised when it is blocked by a long truck slowly accelerating across the intersection. Adequate sight distances are needed at non-signalized intersections to allow the truck driver to assure that cross traffic will not be impeded, and drivers in cross traffic need adequate distance to readily stop should that be necessary. While the highway design guides attempt to provide good rules for design in these situations, there is always room for improvement in highway design practices. More collaboration between highway designers and truck operators could be productive when addressing these issues.

For example, improvements in traffic signal timing would be likely with input from truck operators. One illustration that comes to mind is the timing of yellow caution intervals on relatively high speed highways. Various guides suggest intervals up to 6 seconds. Yet, a loaded truck approaching an intersection at 55 mph needs more than 6 seconds to stop. Thus we create the situation where the driver knows he cannot come to a full stop before the light turns red and he must make the snap decision about whether to proceed in hopes that he can clear the intersection in time.

Truck operator vision and visibility problems are also associated with signing. Highway signs are designed to provide a high reflectance back toward the source of lighting. In passenger cars the driver eye level is not much higher than the headlights that illuminate highway signs. However, on trucks the driver sits quite high. Further, the pressure is on to keep truck headlights low in order to minimize glare in vehicles ahead. The greater difference between headlight and driver eye levels in trucks means that retro-reflective signs are not illuminated as brightly for truck drivers as for others [10]. Reflective materials with broadened reflection angles is needed. Since this problem has been recognized, UMTRI has been working with headlamp manufacturers, the SAE Lighting Committee, and manufacturers of retro-reflective sheeting materials, but its solution would clearly benefit from interaction between the highway and trucking communities.

Noise Control—It is common practice to place noise barrier walls along heavily used truck routes to shield residential areas from the high noise level created by truck traffic. It might be noted that most highway tractors have high-mounted exhaust stacks broadcasting the noise from a height of 12-13 feet. Consequently, noise barriers must be higher, adding to the expense of such measures. Although this issue has been brought to the attention of truck manufacturers, they are not fully capable of resolving the problem, as they must build trucks to the specification of buyers. If buyers want high-mounted stacks the manufacturer must be responsive to that need in order to retain that customer.

In these few examples we see illustrations of the need for better understanding between highway and trucking interests, but the model by which this can happen is not always clear. The vision of building collaborative arrangements under SVID must find solutions to several impediments:

1) The highway community is relatively homogeneous and comprised of public agencies. Thus, cooperation among these agencies is non-threatening.

2) The trucking community is private sector and highly competitive. Each operator is trying to be more productive and efficient in order to gain competitive advantage.

3) The trucking community is quite diverse. The trucks on the road today are designed by manufacturers trying to appeal to a consumer base. The consumer base ranges from individuals to large fleets who have a broad range of transport missions to satisfy. The trucks in turn are driven by individuals who range broadly in their skills and commitment to the public good.

4) Given that the trucking community is so diverse and driven by the need to remain competitive, securing their interest and participation in a cooperative program must rely on well designed programs to provide incentives that are meaningful in that world.

Thus, in order for SVID to succeed it will be necessary to carefully analyze the motivations of trucking interests to seek ways to offer advantages that will improve competitiveness. As a model, one might consider the philosophy of the World Bank in offering loans for less-developed countries to build highway transportation systems. The emphasis in management of those endeavors focuses on total road user costs. In the extreme, this philosophy favors an infrastructure and political will to maximize transportation while minimizing costs. Ultimately, society pays for both the infrastructure and transport costs. As we are making conscious decisions to develop infrastructure or constrain its use, we are making decisions about consuming the economic resources of our industrial base. So long as the goals of maximum transportation and minimum costs are evident, we may be able to attract collaboration from the members of the trucking community.

Insofar as the appeal to the private sector is based on the goal of preserving the infrastructure, there will be limited prospects for success. For even though all road users share an interest in preserving the highway system, at the individual truck operator level there is no payoff for compromising productivity in order to preserve the infrastructure. One must identify goals which are meaningful to the trucking community—goals that fit the competitive environment.

It is suggested that safety is such a goal. Initiatives that improve highway safety (specifically the trucking side) are of interest to truck manufacturers, owners, and operators because each are affected daily by the economic costs of accidents through liability and lost productivity. Even then only certain sectors of the trucking community will take interest in a particular collaborative endeavor.

Consider the matter of arrester ramps on long downhill grades intended to stop runaway trucks. Since runaway is an infrequent event, there may be little interest from individual operators or fleets. However, a fleet that operates from the top of a long grade may have more motivation because the number of its trucks operating on the long grade increases the probability of a runaway. Certainly, a fleet with its yard located at the bottom of the hill in the path of runaway trucks has even more interest.

As illustrated here, as we attempt to envision SVID topics it will be important to analyze and consider the potential motivations for involvement by private sector entities. Although the American private sector supports considerable philanthropy, we cannot expect their cooperation and involvement based simply on altruistic motives.

1) T. D. Gillespie, "Issues in Understanding Truck-Road Damage." Keynote Speech, DIVINE Concluding Conference, Ottawa, Canada June 23-25, 1997

2) M. G. Lay, Ways of the World, A History of the World’s Roads and the Vehicles That Used Them. Rutgers University Press, New Brunswick, New Jersey, (1992), 401 p.

3) "Highway/Commercial Vehicle Interaction: North America and Europe." Study Tour Summary Report, Federal Highway Administration, (March 1996).

4) M. W. Sayers, "VDM RoAD User Reference Manual: Version 1.0." University of Michigan Transportation Research Institute, Draft Report to FHWA, Contract No. DTFH 61-93-R-00142, (1997), 360 p.

5) Fancher, P. S., and T. D. Gillespie, "Truck Operating Characteristics." NCHRP Synthesis 241, (1997).

6) American Association of State Highway Officials, "The AASHO Road Test." Report 7, Summary Report, Highway Research Board Report 61G, (1962), 59 p.

7) Gillespie, T. D., et al., "Effects of Heavy-Vehicle Characteristics on Pavement Response and Performance." NCHRP Report 353, Transportation Research Board, (1993), 126 p.

8) A Policy on Geometric Design of Highways and Streets, American Association of State Highway and Transportation Officials, Washington, D.C., (1990).

9) Gillespie, T. D. and R. D. Ervin, "Safety and Operational Impacts of 53-foot Truck Trailers in Michigan." The University of Michigan Transportation Research Institute, Report No. UMTRI-86-13, (1986), 208 p.

10) Sivak, M. and M. Ensing, "Human Factors Considerations in the Design of Truck Lighting, Signaling and Rearview Mirrors." The University of Michigan Transportation Research Institute, Report No. UMTRI-89-9, (1989), 26 p.