Speed Analysis on Urban Roads

Speed analysis on urban roads sections start from need tied up to traffic assignment models in urban networks: to calculate the average running time in a road section it is necessary to have a good evaluation of average running speed for that road section. First experimentations for the study of drivers «realized» speed (for rural roads) have been published already in 1988. In 1997 it has been published a first expression for «realized» speed in function of curvature (1/R) and of absolute value of the longitudinal road gradient for some typologies of common rural roads. Most greater number of road accidents occurs in city and the gravity of these, often also for urban roads, comes from transit speed. The transit speed in road safety study cannot be the average speed (like for traffic assignment models) but be «realized» one, defined as the 85° percentile of the speed data distribution. In this work it has been considered a number of urban roads with definite characteristics and the effected measurements have allowed to define coefficients for an interpolating speed function. It is carry out, besides, spot speed measurements and, for the same location, average speed measurements (measuring the running time on the whole road) in order to value differences for both methodologies. The significant, even if partial results, will show in the paper.