The New Haven–Hartford–Springfield (NHHS) Line Double Track Program was a major rail infrastructure initiative that improved passenger rail service between Connecticut and Massachusetts through the installation of Positive Train Control (PTC), approximately 40 miles of new track, and the construction and rehabilitation of bridges and culverts along the corridor. Funded by the Federal High-Speed Intercity Rail Program and the State of Connecticut, the project enhanced rail capacity, safety, reliability, and regional connectivity, supporting expanded Hartford Line service and strengthening transportation links throughout New England.