The proposed Project is composed of a suite of capacity improvements along the 27-mile Green Line light rail system, which consists of a trunk section and four branches, and includes surface, elevated, and tunneled sections through some of the densest urban areas in the country. The Massachusetts Bay Transportation Authority (MBTA) plans to deploy higher-capacity Type 10 vehicles to increase the overall capacity of the line. Given the age of the line, significant physical reconfiguration is necessary to deploy the Type 10 vehicles, especially in the tunneled sections.