Foursquare ITP led a study to determine the feasibility of through-running commuter rail service between the MARC and VRE systems in the National Capital region. The two systems provide commuter service in Maryland and Northern Virginia, respectively, and terminate at Union Station in Downtown Washington, DC. Today a growing number of commuters are travelling across state lines to reach employment centers in Maryland and Northern Virginia but the lack of through service means that commuter rail is not a viable option for many of those trips. Moreover, the existing highway and Metro crossings over the Potomac are nearing capacity, raising the need for additional commuter solutions. The VRE-MARC Run Through Feasibility Study is the first step in developing closer integration between the region’s two commuter railroads. Foursquare ITP conducted a market assessment to determine the demand for run-through service and identified key considerations for implementation; engaged with stakeholders to gather feedback on run-through service; and prepared a new modelling methodology to develop ridership projections.