Do trains have gears?

That is a pretty vague question, but we'll assume you are talking about a common diesel-hybrid train, and by gears we'll assume you are asking if a train has a transmission that shifts gears. Short answer: no they don't. Long answer: First, why the diesel engine. Diesel engines are more efficient than gasoline engines, and when you are pulling thousands of tons of cargo, efficiency is crucial to keep down fuel costs. Now why no gears. A typical gasoline powered car has a large RPM range (typically 0-6000) and only a small portion of that range has maximum torque. This requires a transmission to keep close to that max torque through various speeds. With the diesel engine, the RPM range is small (0-100) so it would take too many gears to get the train up to speed. With a hybrid train, the engine can run at a constant speed (maintaining torque) and send electrical power to traction motors that turn the wheels.