NCHRP Task 303  DIRECTORY OF SIGNIFICANT TRUCK SIZE AND WEIGHT RESEARCH

MOTIVATION Decision-makers are challenged to identify/utilize state of knowledge from truck size and weight research Extensive volume of related research, dating back nearly 80 years Breadth of related topic areas including infrastructure preservation, enforcement, safety, congestion, environment, industry costs, modal share, etc. Diverse interests of public and private sponsoring agencies/ organizations

OBJECTIVE To develop a “directory” of significant truck size and weight research that is brief, well-organized, and neutral Address the breadth of all related topic areas Consider research performed by various sponsoring agencies Be organized topically with embedded cross-references directing readers to additional findings NOT be inclusive of all related research Only essential information is included. Each finding is carefully cited to support additional information gathering.

TECHNICAL APPROACH Task 1:Distinguish Relevant, Significant, Useful Research from Body of Research Timeliness Soundness of the methodology Scope and comprehension Conducted in response to an expressed need Task 2:Extract Key Research Findings Methodological strengths or shortcomings that may influence validity of findings Trends or commonalities among publications that suggest a higher level of confidence Conflicting findings that challenge decision-making Task 3:Produce Final “Directory of Significant Truck Size and Weight Research”

FINDINGS Infrastructure Preservation –Pavement –Bridge Modal Share Enforcement Highway Safety Highway Geometrics Industry Costs Infrastructure Financing Highway Congestion Environment Public Opinion

INFRASTRUCTURE PRESERVATION – PAVEMENTS Higher axle weights can significantly increase pavement damage/costs –3-4 exponent power for flexible –11-33 exponent power for semi-rigid/rigid Higher GVWs spread over more axles do not increase pavement damage and can even result in cost savings Multi-axle groups are –Less damaging than single axles for flexible pavements –Unconfirmed for rigid pavements Increased axle spacing within a group –Increases fatigue damage to flexible pavement –Decreases damage to rigid pavements

INFRASTRUCTURE PRESERVATION – PAVEMENTS Pavement damage/costs vary by road classification and pavement design –Example: 5-axle, 80,000 lb tractor semitrailer causes $0.09 damage/mile on rural Interstate Highways $5.90 damage/mile on rural local roads Pavement damage/costs vary seasonally; potential for damage is highest during the spring

INFRASTRUCTURE PRESERVATION – BRIDGES Bridge safety concerns –Overstress—bridge has inadequate load-bearing capacity to accommodate loads (focus of research) –Fatigue—bridge suffers from reduced life attributable to repeated loadings (generally limited to steel structures/ bridge decks) Bridge stress –Is affected more by total load than number of axles; GVWs >80,000 lb can be used without excessive stress –Increases with axle group weight –Decreases with separating distance except on some continuous bridges with long spans

INFRASTRUCTURE PRESERVATION – BRIDGES Bridge upgrade costs may be exaggerated –Assume full replacement over cost-effective alternatives Strengthening the bridge (when viable) Restricting select truck configurations indefinitely along non-essential routes Federal Bridge Formula has been criticized for –Setting overly cautious limits for shorter truck weights –Allowing too much extra weight with additional axles –Allowing trucks that could overstress continuous spans (originally considered stresses on simple-span bridges)

MODAL SHARE Complex, profit-driven, economic relationships –Increased truck limits lead to lower truck transport costs –Industry competition and regulatory pressure translates lower costs into lower transport rates –Rail industry must either match lower rates or lose freight traffic—in either instance, rail revenues will decline Estimates of traffic diversion/rail revenue losses are highly variable and sensitive to –Regional commodity movement/infrastructure conditions –Extent of truck payload capacity increases –Evaluation assumptions

MODAL SHARE Shippers consider price and service –Rail service is almost always less expensive –Truck service offers faster, door-to-door delivery –For low-value commodities—such as coal, grain, or chemicals—price is often a priority over service Highest levels of modal competition exist for –Intermodal operations with combined truck/ rail transport –Carload operations that utilize boxcars

ENFORCEMENT Challenged to accurately relate enforcement and compliance –Reliable estimates of illegal activity are lacking –Wide divergence in U.S. enforcement practices Higher enforcement levels generally associated with higher compliance –Violation rates for fixed Interstate weigh stations <1% when enforcement is present 15% when it is not –Violation rates along bypass routes and/or using mobile enforcement are higher in frequency (30%) and magnitude

ENFORCEMENT Combination of fixed and mobile enforcement can be most effective Greater reliance on technology provides increased spatial/temporal coverage with personnel constraints Laws/regulations that are complex or contain numerous exceptions challenge enforcement and subsequent prosecution

HIGHWAY SAFETY Larger, heavier trucks can affect highway safety by –Increasing/decreasing truck traffic volumes –Changing vehicle design/performance –Causing a shift to alternate road classifications with higher/ lower crash rates Interstates/Turnpikes are generally safer irrespective of truck size or weight Inadequate crash/exposure data limit ability to relate truck size and weight to highway safety Changes in driver qualifications and vehicle/roadway design can potentially offset the safety drawbacks

HIGHWAY SAFETY Larger, heavier trucks generally have –Lower crash rates (attributable to fewer truck trips) –Higher crash severities –Same or slightly higher crash risk based on vehicle handling and stability characteristics Double trailer trucks prone to rearward amplification Higher centers of gravity increase potential for rollover Truck configuration findings are inconsistent –Double trailer trucks have higher/lower/same crash rates and severities –LCVs have higher/lower crash rates and severities; recent research suggests superior safety performance Vehicle stability/control performance measures can help assess safety impacts of larger, heavier trucks

HIGHWAY GEOMETRICS Design features most affected –Horizontal curves –Intersection turning radii –Passing sight distance –Sight distance at intersections/railroad grade crossings –Ramp interchanges Increased trailer lengths increase vehicle off-tracking Wider trucks on rural 2-lane highways elicit undesirable/unsafe actions by oncoming drivers Upgrade costs are highly variable and depend upon –truck configuration –extent of roadway network to be redesigned

INDUSTRY COSTS Increased truck size and weight limits consistently result in estimated industry cost savings Magnitude of cost savings varies by –carrier type –nature of transportation services offered –commodities transported Truckload carriers and low density cargoes benefit most from larger truck sizes Estimated industry cost savings range from 1.4 to 11.4 percent of annual U.S. transport costs

INFRASTRUCTURE FINANCING Predominant truck-focused alternative financing strategies include –Tolled facilities –Weight-distance based road user fees –Container and/or U.S Customs and Border Protection fees Industry is highly fragmented—any alternative financing strategy will likely evoke varied reactions With some consistency, industry favors truck-only tolled or shared facilities that provide operational advantages (e.g., increased size or weight limits) –Toll facilities that offer only congestion avoidance benefits are insufficient in overcoming increased operating costs

INFRASTRUCTURE FINANCING Weight-distance based road user fees are commonly based on registered not actual truck weights –Levies on registered GVW may promote higher logistical efficiency by discouraging “empty” trips, but this effect has not been considered or reported in the literature –Current technology (WIM systems) allows capture of actual weight, making fees more equitable in terms of potential infrastructure damage –Weight-distance based road user fees have been demonstrated to generate more revenue than mileage- based registration fee systems

HIGHWAY CONGESTION Larger, heavier trucks can affect highway congestion by –Decreasing heavy truck VMT with increased truck capacity –Increasing heavy truck VMT in response to lower transport costs –Decreasing highway capacity as a result of compromised maneuverability and less horsepower relative to weight Larger, heavier trucks are predicted to modestly degrade traffic flow and capacity—anticipated reductions in heavy truck VMT likely offset these negative impacts Prior studies have been criticized for oversimplifying interactions between trucks and other vehicles

ENVIRONMENT Environmental impacts typically characterized as –energy consumption –harmful emissions –noise levels Estimates are often derived from anticipated reductions in heavy truck VMT Fuel consumption and CO 2 production generally decrease with increased truck size and weight Other harmful emission impacts are largely inestimable using contemporary models Noise levels have been shown to both increase and decrease with increased truck size and weight

PUBLIC OPINION Public opinion is largely shaped by safety-related media campaigns –Despite marked improvement over time, majority of drivers express safety concerns regarding large trucks Based on limited studies, increases in truck size rather than weight are of more concern –Increased truck size—particularly length—is more visible and perceived to affect safe passing maneuvers and truck driver visibility –Incremental changes in truck weight will likely not affect survivability in a collision

PUBLIC OPINION Majority prefer status quo on Federal truck size and weight limits—or a return to more restrictive limits if any changes are to be made Enforcement of existing truck size and weight regulations perceived to be inadequate –Public lacks confidence that any increased limits could be controlled

QUESTIONS