Conrail's daily Corning, NY to Allentown, PA freight is about to duck under the Lehigh Street overpass in North Catasaqua, PA. Leading the train is Conrail's "class unit" SD60. 6840 was one of three SD60s on the roster that were first used as EMD demonstrator units before being assigned to Conrail. As such, these units were slightly different from all other Conrail SD60s. Conveniently, the second unit in this consist is a more typical unit which provides a good comparison. Note the standard classification lights on 6840 (vs. red FRA marker lights on 6844), different air horn placement and different color number boards.
The EMD SD (special duty) series are a strong and reliable kind of locomotive which still serve America's rails today. They have proved themselves reliable by clocking in several million miles of freight service.