Extensive electrification after 1925 occurred on the PRR's New York-Washington line (now part of the Northeast Corridor), the Chicago-Philadelphia Main Line between Paoli and Harrisburg, several major commuter lines in Pennsylvania and New Jersey, and on major low-grade, through-freight lines, including the Trenton Cutoff, the Atglen & Susquehanna, Port Road, Philadelphia & Thorndale, Shellpot, and Enola branches. All electrification done after 1919 used the same catenary supports used on the Paoli commuter line, but with the catenary being supplied with "transmission" lines with the voltage stepped-down at substations located every . The PPL-owned Safe Harbor Dam, located near the Exelon-owned Peach Bottom Nuclear Power Plant between Conowingo, Maryland and York, Pennsylvania, supplies the power for all post-1925 electrical expansion projects, while Exelon supplies the pre-1925 electrification areas through the existing Philadelphia, Ardmore, and Chester substations. Plans were made in the thirties to extend electrification to Pittsburgh, but were not pursued due to the Great Depression.