AECOM developed the Northern Virginia Simulation Model in direct response to recent changes in Virginia law that require an analysis and rating of significant highway, transit, and technology projects in Northern Virginia based on the degree to which each project is expected to reduce current and future congestion levels and improve mobility during an evacuation emergency. The model development was managed by the planning staff in the Northern Virginia District of the Virginia Department of Transportation (VDOT) and coordinated with the Commonwealth Transportation Board (CTB), the Department of Rail and Public Transportation (DRPT) and the Northern Virginia Transportation Authority (NVTA). Briefings to the northern Virginia delegation of the General Assembly and other primary stakeholders were conducted at important decision points throughout the project.
The model was used to evaluate 37 transportation projects nominated by the NVTA based on the priorities of the CTB. The evaluation process was performed using rigorous analytical techniques and transportation models critiqued by a Peer Review Group established by VDOT. This group includes subject matter experts from universities and other transportation institutions from outside of the Commonwealth of Virginia.
The overall analytical process starts with a regional modeling process derived from the Metropolitan Washington Council of Governments (MWCOG) travel model (version 2.3) and Cooperative Land-Use Forecasts (Round 8.2) that feeds demand and basic network attributes into a regional simulation process based on the TRANSIMS software. This approach disaggregates the demand data to specific times of day and activity locations and assigns highway and transit trips to a time dependent network that includes operational features such as traffic signals, HOV lanes, and transit schedules. The results are typically aggregated to 15 minute time increments throughout the day to quantify the impacts of capacity constraints on queue spill-backs and travel speeds. This permits the quantification of system performance and the severity, duration, and distribution of congestion in a much more detailed and realistic way than a traditional travel demand forecasting model can produce.
In additional to a regional simulation of system-wide performance measures throughout the day, some projects required detailed analysis of specific operational issues at key bottleneck locations. For this analysis, the demand generated by the regional simulation was extracted for a small subarea at the bottleneck location and a more detailed analysis performed using the VISSIM traffic operational tools.