High speed offtracking (diagramed below) is dangerous. When a tractor-semitrailer is traveling on a curve at highway speeds on the winding mountainous roads, the back of its trailer could sideswipe other vehicles traveling in adjacent lanes or stopped cars sitting on the highway shoulder. When trucks negotiate freeway exit ramps at high speeds, the tires of the trailer's rear axles may strike the curb, leading to a rollover. HIGH SPEED OFFTRACKING DIMENSION High speed offtracking for tractor-semitrailers increases as gross weight increases.17 Trucks typically accelerate more slowly than cars and have more difficulty maintaining desirable speeds on long, steep upgrades. The most important factor affecting truck speed on upgrades is the weight-to-horsepower ratio (gross truck weight divided by net horsepower). 17 Fancher et al., 1989, supra note 9, p. 74. 18 Transportation Research Board, National Research Council, Truck Weight Limits, Special Report 225, 1990, p. 117. Slower speeds are dangerous. They lead to more sudden brake applications, more overtaking and more lane changing attempts by vehicles stuck behind the slowly moving trucks. These slow truck speeds also cause disruption as the trucks themselves change lanes. Studies demonstrate that these slower speeds are much more dangerous than is commonly understood. A University of Texas study concluded that trucks which travel 15 mph below the prevailing speed of other vehicles have crash involvement rates nine times higher than those that travel at the same speed as other traffic. The same study found that the crash involvement rate is 15 times higher if the speed differential is 20 mph.' 19 Data on rear-end crashes compiled and analyzed in a U.S. Government study showed that the rates of rear-end crashes increased sharply when speed reductions exceeded 20 mph.20 Because of their length and slow acceleration rates, tractor-semitrailer trucks take longer to merge into freeway traffic from an onramp than do cars and small trucks. Acceleration lanes (merge lanes which allow vehicles coming from onramps to build up enough speed to easily merge with other vehicles already on the freeway) are designed primarily for cars and are already too short for 80,000 pound trucks.21 Heavier truck weights will mean that trucks will have to slow down or stop even more frequently than they do now to find a gap in traffic large enough to allow them to merge. This will result in traffic backup and disruption. It will also increase the probabilities of crash by increasing levels of traffic conflicts." To compensate for inadequate acceleration lane length, truck drivers may have to speed up while traveling the latter portion of interchange ramps to gather speed high enough for 19 C. M. Walton and O. Gericke, "An Assessment of Changes in truck Dimensions on Highway Geometric Design Principles and Practices," The University of Texas Center for Transportation Research, Austin, 1981. 20 D. Solomon, "Accidents on Main Rural Highways Related to Speed, Driver and Vehicle," U.S. Department of Commerce, 1964. 21 Transportation Research Board, supra note 6, p. 119. 22 Id. at p. 118. merging. Especially on ramps with sharp curves, this can threaten loss of control on the curves. Heavier truck weight causes similar problems when truck drivers need to change lanes on busy freeways. IIL CONCLUSION Studies conducted by government agencies, university research centers and independent boards demonstrate that an increase in gross vehicle weight would substantially increase the likelihood of truck crashes throughout the country. Heavier trucks would be more susceptible to rollover, runaway, serious braking problems, merging and other problems. The Congress should reject any proposal to allow overweight trucks on our nations highways. 84-609-94-6 APPENDIX The following chart shows the "rollover threshold" for tractor-semitrailer trucks at gross vehicle weights varying from 73,300 to 92,000. Rollover threshold represents the amount of force that a tractor-semitrailer can withstand when going around a curve or making a sudden obstacle avoidance maneuver without rolling over. The lower the rollover threshold, the more likely it is that a truck will rollover.24 The following graph shows that as the rollover threshold for a tractor-semitrailer becomes lower (worse), the rollover crash rate increases at an almost geometric rate.25 "R.D. Ervin et al., supra note 3, figure 30, p. 80. 25 P.S. Fancher et al., "Turner Truck Handling and Stability Properties Affecting Safety," Final Report, Vol. I, Technical Report, University of Michigan Transportation Research Institute, July 1989, Figure 3.1, p. 9. ADVOCATES AND AUTO SAFETY STATEMENT OF GERALD A. DONALDSON, PH.D., SENIOR RESEARCH DIRECTOR, COMMITTEE ON PUBLIC WORKS AND TRANSPORTATION, UNITED STATES HOUSE Let me Thank you, Mr. Chairman, for providing Advocates for Highway and Auto Safety with the opportunity of testifying on truck safety issues before the Subcommittee on Surface Transportation. state here at the start that truck safety would be advanced both for the trucking industry as well as for the travelling public by the enactment of H.R. 4496. Advocates strongly supports the truck safety legislation that is being championed by Congressman James Oberstar in the Safe Transportation and Infrastructure Preservation Act of 1994. We are an alliance of common purpose between the automobile property and casualty insurance industry and a wide array of consumer advocates, public health experts, law enforcement authorities, and other organizations and individuals who care deeply about reducing the unacceptable losses we sustain each year from crashes on our streets and highways. Advocates has entered its fifth year of operation as a organization that acts at both the state and federal levels to achieve improved highway and vehicle safety laws and regulations. We are here today to ask you, this committee, and this Congress to act strongly to put an end to the accelerating increases in truck sizes and weights. legislation is an opportunity for Congress to place appropriate Congressman Oberstar's 777 North Capitol Street, NE Suite 410 Washington, DC 20002 Tel: 202/408-1711 Fax: 202/408-1699 |