A large generator remained at the end of the long diesel engine. Such a combination is significant of an electro-diesel locomotive, meaning that this particular railway vehicle is capable of dual power; diesel or electric operation. The rational behind the hybrid engine design was that the locomotive could travel on electrical rail lines sporting a third rail as well as switch to normal diesel power. This is advantageous because in many city tunnels such as in NYC, diesel exhaust is prohibited, so electoral power would be used until out of city limits.