VCI, a Regional Volume/Capacity Index Model of Urban Congestion

This paper proposes a simple model of regional average congestion delay as a closed-form differentiable function of published regional transportation system volume and capacity. Three initially undefined parameters are calibrated by regression to best match the regional congestion delay estimates of Texas Transportation Institute’s (TTI) “mobility” analysis of 85 U.S. urban regions. The model fits the TTI delay data quite well with goodness of fit parameter Ra2 =86% and standard error of congestion delay estimate 0.046 min/mi. The model is analytic, that is, differentiable as opposed to discrete data tables. Use of the model is illustrated by closed-form estimates applicable to any urban area with numeric examples of several region descriptive statistics of interest including (1) regional total and average congestion delay for a region not in the TTI ensemble; (2) marginal congestion benefit of freeway lane-mile capacity addition and benefit/cost; (3) capacity addition necessary to improve the region to m...