The four-axle units are being rebuilt from EMD GP50 locomotives in a project partially funded by the federal Congestion Mitigation and Air Quality Improvement Programme (CMAQ).

The locomotives are being repowered with 12-cylinder 2.24MW EMD 12N-710G3B-T3 prime movers, which are compliant with US Environmental Protection Agency (EPA) Tier 3 emissions standards. Each unit is also equipped with an EMD EM2000 microprocessor control unit, a new electrical cabinet, a ZTR SmartStart engine stop-start system and a new cab which is compliant with current Federal Railroad Administration crashworthiness standards.

Following testing in the Altoona area, the first two units will be despatched to Chicago and Atlanta where they will be used for shunting operations in marshalling yards.

Funding for the 15 locomotives for the Chicago area was awarded by the Chicago Metropolitan Agency, sponsored by the Illinois Environmental Protection Agency, and administered by the Illinois Department of Transportation. Funding for the 10 Atlanta locomotives was awarded by the Georgia Department of Natural Resources Environmental Protection Division.