A highway expansion and transit project for the southern I-25 corridor, dubbed T-REX (Transportation Expansion Project), was completed on November 17, 2006. The project installed wider and additional highway lanes, and improved highway access and drainage. The project also includes a light rail line that traverses from downtown to the south end of the metro area at Lincoln Avenue. The project spanned almost 19 miles (31 km) along the highway with an additional line traveling parallel to part of I-225, stopping just short of Parker Road.
Denver is in the center of the Front Range Urban Corridor, between the Rocky Mountains to the west and the High Plains to the east. Denver's topography consists of plains in the city center with hilly areas to the north, west and south. According to the United States Census Bureau the city has a total area of 155 square miles (401 km2), of which 153 square miles (396 km2) is land and 1.6 square miles (4.1 km2) (1.1%) is water. The City and County of Denver is surrounded by only three other counties: Adams County to the north and east, Arapahoe County to the south and east, and Jefferson County to the west.