This paper investigates the relationship between congestion and accidents. Factors that influence the number of highway fatalities are speed, speed variance, and traffic composition. The paper examines specifically the congestion impact on the number of fatalities. The lower speeds which are caused by congestion would produce lower fatal accident numbers. As a result, a parabolic relationship between density and fatal highway accidents is expected. When densities increase, there would be first a positive relationship due to the increase in the numbers of cars in the system. However, when density becomes so high that speeds are influenced negatively, the number of fatal accidents will decrease. In addition to the negative congestion impact in terms of time losses, there would be a positive impact, since fatalities are reduced. Some supporting evidence is found for a number of countries where relatively low fatality numbers are observed during the morning peak.
Abstract