Modern freight trains rely on a diesel‑electric hybrid. The large, turbo‑charged, two‑stroke diesel engine runs at a steady, low rpm, driving a high‑voltage generator. The generator feeds traction motors on each axle, delivering power directly to the wheels. This arrangement eliminates the need for a multi‑speed gearbox, allowing the locomotive to accelerate smoothly from a standstill to 125 mph (200 kph) without gear changes.
Diesel engines are up to 20 % more thermally efficient than gasoline engines. For rail, this translates to roughly four times the fuel economy of trucks: a CSX locomotive can haul 1 ton of cargo for 492 miles on a single gallon of diesel. Diesel‑electric locomotives are also about five times more efficient than the steam engines that preceded them.
Railways use steel wheels on steel rails because the contact patch is tiny—roughly the size of a dime—minimizing deformation. Steel‑on‑steel contact reduces rolling resistance to well below 1 %, making trains the most energy‑efficient mode of heavy freight transport. The trade‑off is lower traction, which is addressed by the traction system described below.
Each of the locomotive’s eight traction motors can produce over 60,000 lb‑ft of torque. To prevent wheel slip during acceleration or braking, the locomotive uses a sand‑spray system and an electronic traction‑control unit. When slip is detected, sand is ejected onto the rails and the system reduces power to the affected motors.
The EMD 710 engine features:
Its two‑stroke cycle delivers twice the power per revolution compared to a four‑stroke engine of similar size, enabling continuous operation for decades.
Propulsion: Traction motors drive the wheels via gear reduction, allowing speeds up to 125 mph. Each motor can draw >700 A.
Suspension: A combination of leaf or coil springs, pivoting bearings, and lateral links dampens track irregularities, reducing wear and improving ride quality.
Braking: Air‑powered drum brakes provide mechanical stopping power, while dynamic braking turns the motors into generators, dissipating kinetic energy as heat through resistive meshes. A hand brake on the rear truck serves as a safety backup.
Amtrak, the national passenger rail operator, is modernizing its fleet with dual‑power locomotives that run on diesel or electrified lines. The new bi‑level “Superliner” cars offer spacious seating, dining services, and sleeper cabins, providing a comfortable alternative to air travel. Amtrak’s rail‑car storage service allows passengers to bring a vehicle on select routes.
A diesel locomotive combines a diesel engine that powers an electric generator with traction motors that turn the wheels.
Modern locomotives generate around 3 200 hp, which the generator converts to approximately 4 700 A of current for the traction motors.
A traditional locomotive relies solely on mechanical transmission. A hybrid diesel‑electric locomotive uses electrical generation to drive the wheels, providing higher efficiency and smoother power delivery.
Diesel engines have higher compression ratios, delivering 20 % more thermal efficiency than gasoline engines, and they can run continuously at low rpm for decades.
Steel wheels on steel rails reduce rolling friction to below 1 %, conserving energy and extending operating life compared to rubber tires.
