At that scale I think ICE engines preferably run at the same RPM continuously, and a gearbox and a clutch would be massive and require a lot of maintenance. The

At that scale I think ICE engines preferably run at the same RPM continuously, and a gearbox and a clutch would be massive and require a lot of maintenance. The electric motor gives you the huge amount of torque you need to get a train going from stand-still. Not sure what actually tips the scale though.