The MPI MP8AC-3 is a lightweight diesel-electric locomotive built by the MotivePower division of Wabtec.

The R156 is designed to navigate the clearances and tight turns of the NYC Subway, with weight constrained to 112,000 pounds (51,000 kg), so it can operate on elevated portions of the system.

[4] A separate, smaller John Deere Diesel drives a generator to provide auxiliary power and to heat the main engine and keep batteries charged when the main engine is not running.

Trucks are supplied by Kawasaki, which provides the same wheel and traction sets for the R160 subway cars.

[3] Media related to MPI MP8AC-3 locomotives at Wikimedia Commons