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Speed is only one of several factors affecting the occurrence of accidents. For example, much of the German Autobahn does not have a speed limit, yet the traffic fatality rate is lower than the fatality rate for US Interstate Highways. The object of this paper was to review relevant accident data in order to establish a relationship between speed limits and accident rates, so as to facilitate a rational approach towards the setting of speed limits for the U.S. Interstate Highways. Our results indicate that the main parameters effecting traffic accidents are: (a) Road design, (b) Driver alcohol consumption, (c) Seat belt usage. Speed limits were found to have minimal effect on the traffic accidents. The evidence also indicates that separate speed limits for day-time and night-time as well as for dry road and wet road would enhance safety much more significantly than the enforcement of speed limits that are set too low.

Vehicle corrosion costs the public billions of dollars each year. The severity of vehicle corrosion is strongly affected by the amount of salt to which the vehicles are exposed. The main sources of the salt causing vehicle corrosion are the atmosphere and road salting. Some geographical areas experience minimal corrosion problems, but in other areas the corrosion problems are more severe. Knowledge of the severity of corrosion in a given geographical area is important when decisions are made about corrosion prevention and when corrosion related recalls/modifications are initiated. The object of this paper is to review the existing literature on corrosiveness in various geographical areas and propose a rational corrosion severity map.

An estimate of the rate of attrition of passenger cars, needed to establish the service life expectancy of passenger cars, is of major interest whenever long range production plans are made, marketing strategies are developed, the total needs of vehicles on the roads are estimated, etc. Estimation of vehicle attrition is very complex, however, due to the lack of accurate data and the interaction of the parameters affecting attrition. In 1980 and 1985, similar studies of attrition [1,2] utilized vehicle registration data available as of July, 1979 and as of July, 1984. The object of this paper is to update the results of these papers, using the 1991 July registration data, available in May 1992. Within the scope of this paper the attrition rates of various passenger cars are compared and the effect of geographical location on the attrition rates and the change in attrition rates during the past twenty years are discussed.

The approximate population of passenger cars in service and the rate of attrition of that population must be known when long range production plans are made, marketing strategies are developed, the total fuel need of the vehicles on U.S. roads is estimated, etc. Estimation of population is complex due to the lack of accurate data and the interactions between the parameters affecting attrition. Various methods are available to estimate the present and future population levels of passenger cars in service. Within the scope of this paper the projected populations of various passenger cars are compared and various attrition projection methods are discussed.