WIT Press

60 Kph Minimum Speed Limit On Rural Interstate Freeways: Is It Relevant?


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R. Mussa


The State of Florida, USA, has a practice of posting a maximum speed limit of 105 kilometers per hour (kph) and a minimum speed limit of 60 kph on rural interstate freeways. The results of safety and operational evaluation on these freeways showed that while only 0.14% of recorded vehicles had speeds below the 60 kph posted minimum speed limit, 9% of crash-involved vehicles were estimated to have speeds below 60 kph. The overrepresentation of slow moving vehicles in the crash data suggests that even a small proportion of under 60 kph vehicles can have negative implications on safety. Thus, regulation of vehicle speeds at the lower end of speed distribution is equally important. The Poisson regression modeling indicated that the difference between the 85th and 15th percentile speeds had a positive effect on crashes. Keywords: speed limit, polynomial modeling, Poisson modeling, freeway operations, traffic crashes. 1 Introduction The posting of minimum speed limit signs on roadways is based on the desire to reduce speed variance among vehicles, particularly on high speed roadways. Numerous studies have shown that there is a relationship between crash occurrence and speed variability [1,2,3,4,5]. The State of Florida currently posts a maximum speed limit sign of 105 kph and a minimum speed limit sign of 60 kph on rural Interstate freeways. It seems logical to question the relevance of such a wide gap (45 kph) between the two speed limits thus leading to the assessment of safety and traffic operating characteristics on these sections. Based on the review of previous literature, it could be hypothesized that a wider gap between maximum and minimum speed limits might be creating a number of


speed limit, polynomial modeling, Poisson modeling, freeway operations, traffic crashes.