Urban Traffic Speeds—I: A Comparison of Proposed Expressions Relating Journey Speed to Distance from a Town Center

Abstract

One of the best descriptors of traffic in a town is its speed and some knowledge of the way that it varies is clearly of interest and importance. This paper compares the suitability of five formulas that relate journey speed to distance from a town center for six towns in England and Wales. The formula that gives the most consistently good fit to the data from the towns studied here is of the form v = a − be^cr, where v is journey speed at radial distance r, and a, b, c, are constants. However, a formula of the power form v = ar^b also provides a reasonable description of the data from the towns studied. Although not necessarily being the best fitting formula for individual towns, the ease of use and interpretation of this power function and the fact that it requires only two constants may make it preferable for many studies of the variation of speed within towns. The disadvantage that this formula predicts zero speed at a town center is of little practical importance, since in practice, it can give fairly good estimates of the time taken to reach points in the neighborhood of the town center. It is also concluded that the wide variation of speeds at any particular distance from the center of the one town for which this was examined can be partly explained by the variation between radial routes.