A train engine requires about a hundred litres of fuel to get it started. So it wouldn't be economical if the engine is stopped and started frequently. This apart, if the engine is stopped, the moving parts' lubrication will also come to a halt.
Idling switchers use between 3 and Il gallons of fuel per hour depending on the ambient temperature. If a switcher idles 12 hours a day in warm weather and burns 3 gallons of fuel per hour, it would consume 36 gallons of fuel per day.
The life expectancy of diesel-electric and electric locomotives is expected to be similar—about 25 years. Both types of motive power are subject to technological obsolescence.
Each motor drives a small gear, which meshes with a larger gear on the axle shaft. This provides the gear reduction that allows the motor to drive the train at speeds of up to 125 mph. Each motor can weigh over 6,600 pounds (3,100 kilograms) and draw more than 700 amps of electrical current.
Engines may be left idling to maintain important safety related functions such as maintaining engine temperature, air pressure for the brake system, the integrity of the starting systems, the electrical system and providing heating or cooling to a train's crew and/or passengers.
Freight trains in the US are often powered by two or more diesel units, each about 4400 horsepower. Those units are each supposed to burn around 210 US gallons per hour when they're producing full power.