NCHRP 20-07 Task 303 DIRECTORY OF SIGNIFICANT TRUCK SIZE AND WEIGHT RESEARCH.
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Transcript of NCHRP 20-07 Task 303 DIRECTORY OF SIGNIFICANT TRUCK SIZE AND WEIGHT RESEARCH.
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NCHRP 20-07 Task 303
DIRECTORY OF SIGNIFICANT TRUCK SIZE AND WEIGHT RESEARCH
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MOTIVATION
Decision-makers are challenged to identify/utilize state of knowledge from truck size and weight research
• Extensive volume of related research, dating backnearly 80 years
• Breadth of related topic areas including infrastructure preservation, enforcement, safety, congestion, environment, industry costs,modal share, etc.
• Diverse interests ofpublic and privatesponsoring agencies/organizations
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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.
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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”
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FINDINGS
• Infrastructure Preservation– Pavement– Bridge
• Modal Share
• Enforcement
• Highway Safety
• Highway Geometrics
• Industry Costs
• Infrastructure Financing
• Highway Congestion
• Environment
• Public Opinion
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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
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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/costsvary seasonally; potentialfor damage is highest during the spring
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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
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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)
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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
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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 modalcompetition exist for– Intermodal operations
with combined truck/rail transport
– Carload operations thatutilize boxcars
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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
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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 containnumerous exceptionschallenge enforcementand subsequent prosecution
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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
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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
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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
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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
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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
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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
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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
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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 CO2 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
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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
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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
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QUESTIONS