Safety Analysis of Florida Rural Interstate Freeway Travel in Relation to the 65km∕h(40mi∕hr) Minimum Speed Regulation

Abstract

The relevance of posting the 65km∕h(40mi∕hr) minimum speed limit signs on rural interstate freeways in Florida is analyzed by correlating safety and traffic operating characteristics. Analysis of the lower end of speed distribution showed that only 0.14% of the vehicles were traveling at speeds below 65km∕h. However, a four-year data study of reported crashes showed that the percentage of total crashes involving vehicles with speeds less than 65km∕h was 9%. The overrepresentation of the slow moving vehicles in the total number of reported crashes raises concerns for the safety implications which could result in the aftermath of raising the minimum speed or scrapping the posting practice as 25 other states have. Further research results indicated that the 15th percentile speed on these freeways sections was 95km∕h(60mi∕hr). It is worth noting that it has been suggested in the literature that the 15th percentile speed should be used as a guide in setting the minimum speed limit on freeways. Further analysis showed that the 16km∕h(10mi∕hr) speed range with the most crashes was considerably lower than the 16km∕h speed range for data collected in the field. This paper further reports on Poisson regression modeling conducted to determine the influence of various speed attributes on crashes occurring on rural interstate freeways in Florida.