What's curious is it's a subway car which is presumably not pulling 50 coal hoppers or whatever. The motors should not be dissipating so much power that they sizzle.
Couple more ideas.
Lift chassis and manually rotate each flywheel several times in each direction. Does "transmission" feel smooth and un-impeded? Both flywheels should feel the same mechanical resistance as you turn it. The idea here is that if the engine is behaving properly (you command 10 sMPH, it goes 10 sMPH, and so on), then a sizzling motor means too much electrical power is going in for mechanical work going out.
I like GRJ's idea of simply pulling the motor-plug with the 2 yellow and 2 white wires to the motors. With the connector off, if you have a meter that measures resistance, measure each motor at a handful of angles of a flywheel revolution. Not sure what motors are used in your subway but the resistance should be 10 Ohms plus or minus (that is, not 1, not 100). These are brushed/commutated can motors so there will be different windings in play but the winding resistance should match within a few tenths of an Ohm within a motor and even between motors of the same type. The idea here is some kind of electrical fault with the motor is causing a huge drop in efficiency. Of course hard to believe the same fault would exist in both motors but this should only take a minute or so to confirm so why not.
If you don't want to mess with pulling wires and don't have electrical measurement tools, I'm next thinking of having you operate in conventional mode with speed control turned OFF. This will reveal a lot about motor performance. It's an overlooked troubleshooting method that you can only do in conventional mode in PS2 - you can't turn OFF speed control in DCS command mode. You need a transformer/controller that has Whistle and Bell buttons though. More on this if needed.