Identifying traffic count posts for origin-destination matrix adjustments : an approach to actual-size networks

For transportation planners, the use of Origin-Destination (OD) matrix adjustment, is receiving considerable attention. However, there are concerns about the validity of results, primarily related to the number and location of traffic count posts. This leads to the question “What would be the best set of traffic count posts to use in OD matrix adjustment modules?” It has been proved that solving this problem is cumbersome. There have been several attempts (either exact or heuristic approaches) to address this problem. But due to the inherent complexities, there is no efficient and easy-to-use methodology able to address situations on the scale of actual cases. This study demonstrates a simple way of identifying traffic count posts tailored to deal with real-size cases. The proposed methodology is based on a maximum matrix coverage criterion. Using a limited number of incremental trials, a set of links whose traffic flows give maximum coverage of the demand and maximum fitness to the corresponding traffic count rates are identified as traffic count posts. The results show that more traffic count posts do not necessarily yield a better result. This article reports on a project conducted for the public works ministry of the UAE city of Sharjah.