D2 Subway is a proposed 2.4 miles (3.9 km) expansion of the DART light rail system in metropolitan Dallas, Texas, in the United States.

In 2021 DART reconfigured the project's eastern approach to continue into the existing Cityplace/Uptown station tunnel, foregoing the planned surface junction near Deep Ellum.

Upon leaving the station, the alignment would cross under Spur 366/Woodall Rodgers Freeway and after crossing McKinney Avenue, located on the other side of the highway, the alignment would begin its transition underground through the "west tunnel portal", passing under Hord Street near the Dallas World Aquarium and remaining underground for its duration.

Before passing under South Pearl Street, the alignment would begin to turn northeast, crossing diagonally underneath existing buildings and structures.

The project would include four new DART stations: one at-grade, and three underground which would consist of center platforms and introduce fare barriers.

Services would continue to operate with two- or three-car length trains and not require an additional increases in fleet size beyond the current 163 Kinki Sharyo SLRV cars.