Application for Post Processing of Travel Demand Forecasts for Estimating Express Lane Traffic and Variable Toll Rates

Regional models provide reliable estimates of overall corridor volumes and the distribution of traffic on a network. However, existing regional travel forecasting models do not forecast hour-by-hour traffic volumes and most forecast only total daily traffic. Since the distribution of traffic between express lanes with a user fee (toll) and general use lanes depends heavily on hour-by-hour traffic conditions, additional analysis is required to properly represent these conditions. In addition, express lane toll levels vary based on traffic volumes and thus the supply-demand equilibration process needs to include supply functions that allow both time and cost to vary dynamically. While hourly traffic forecasting with dynamic tolling could be done with a regional network model, the required computing time would be substantial and would limit the ability to test the many scenarios associated with these projects. The spreadsheet-based procedure described in this paper estimates hour-by-hour general use and express lane traffic using daily or period-specific corridor volumes forecast by a regional travel forecasting model. The Express Lane Time-of-Day (“ELTOD”) procedure’s primary inputs are total daily corridor traffic, geometric configuration of the facility, and tolling policy. ELTOD estimates the split occurring between general use and express lanes corridor volumes by solving for supply/demand equilibrium for each hour. Changing ELTOD parameters can test a variable pricing strategy for demand management to preserve a desired level of service in the express lanes when there is an adjacent non-tolled facility as an alternative. This ELTOD application was applied to a current Xpress Lanes project in southwest Florida on Interstate 75.