Speed and Accidents
For many years, highway professionals have known that highway safety could best be achieved by minimizing traffic turbulence and speed variance. Cooperative research by the Bureau of Public Roads and several State highway departments in the late 1950’s and 1960’s verified these views. Both two- and four- lane main rural highways without control of access, as well as urban and rural freeways, exhibited the lowest accident involvement rate for vehicles operating near the average speed for all traffic. For vehicles traveling at both lower and higher speeds, the involvement rate increased sharply. For example, at speeds 15 miles per hour below the average speed on Interstate highways, the accident involvement rate was five times as great as for vehicles operating at the average speed. When an accident occurred, the severity increased with speed, particularly at travel speeds above 60 miles per hour. The chance of being killed in an accident was found to be about four times as great at travel speeds of 73 miles per hour or higher than at 60 miles per hour.[1] These findings have been particularly useful in stimulating official and public awareness of the effects of speed.
Driver and Vehicle Characteristics
In addition to speed, studies showed that other characteristics for groups of drivers and vehicles were directly related to accidents on two- and four-lane main rural highways without control of access. Included were age, sex, and residence of driver; type, age, and horsepower of vehicle; and the seat location of individuals within passenger cars.
It was found that local drivers tend to have higher accident involvement rates than out-of-county drivers, particularly at night, and that drivers of passenger cars with low horsepower have higher involvement rates than drivers of cars with higher horsepower, regardless of several other variables studied, including travel speed.[2]
Highway Safety Study
In the late 1950’s in response to a congressional requirement, a comprehensive study of highway safety was undertaken by the Bureau of Public Roads. The report included a discussion of the traffic accident problem and its setting, review of the highway transportation system, evaluation of current highway safety activities, and a brief description of an adequate highway safety program. Results of this study were used to expand the Federal role in highway safety, including creation of a special National Highway Safety Bureau in the Federal Highway Administration, and eventually creation of the National Highway Traffic Safety Administration. Also, a nationwide computerized system was developed for identifying drivers with suspended or revoked licenses attempting to obtain drivers’ licenses in other States.
Other Safety Research
Other important studies have delineated the cost of traffic accidents in considerable detail, permitting development of useful benefit-cost analyses of various safety problems. Studies related to sizes and weights of trucks in connection with the speed study mentioned earlier have been useful in justifying a combined reduction in speed to 55 miles per hour to save fuel and lives coupled with a 10 percent increase in allowable axle and gross weight limits on the Interstate System to further save fuel and reduce freight haulage costs.
Since 1970 research studies have provided methods for designing improved guardrails, median barriers and bridge rails, criteria for safer roadsides, improved highway lighting, improved traffic signal configurations, warrants for enhancing safety at rail-highway grade crossings, use of earth heat to melt snow, crack detectors for bridges, and driver aids in fog. Also, there has been increased attention to pedestrian and bicycle safety, including the development of bicycle safe grate inlets for city streets, wide dissemination of a bikeway state-of-the-art and evaluation of several pedestrian countermeasures.
The in-motion vehicle weighing and measuring system obtains a description of the traffic traversing the area — number of vehicles, speed and classification (car or truck). Then the weight and dimension subsystems add a complete description of the truck portion of the traffic, including height, width, length, axle spacing and weights, vehicle type, loading, etc. Installations such as this are being used in Texas and as demonstrations in several other States.
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