Carpool Assignment Technique Application

A technique to determine the usage of carpools on high occupancy vehicle (HOV) lanes has been developed for the Washington, D.C., region, but can be applied to any metropolitan area. Planning and testing HOV facilities is an important part in performing an alternatives analysis of future transportation systems. The approach is to adjust zone‐to‐zone average car occupancies, which are output from the traditional four‐step transportation planning process, using an observed relationship between HOV travel time savings and increased car occupancies. These “new” average car occupancies can then be used to develop discrete trip tables by vehicle occupancy sizes based on Washington, D.C., data for corridors with and without HOV facilities. These trip tables stratified by vehicle occupancy sizes can then be loaded to a highway network using a traffic assignment computer program called MULTILOAD. This program available through the Metropolitan Washington Council of Governments loads up to four trip tables to a network using capacity restraint based on the total assigned volume, and produces assigned volumes for each carpool size on every link in the network.