Highway Fatal Accidents and Travel Densities

The fatal accident rate on rural highways should theoretically increase with an increase in travel density. One empirical study of this relationship, however, reported a negative correlation. This correlation is suspect because a common component, vehicle-miles, appears in the denominator of fatal accident rate and in the numerator of travel densities. In our paper two alternative methods of correlation were used, but still no evidence for a positive relationship was found. Apparently certain density associated variables, such as quality of emergency medical service, counteract the theoretically expected trend.