Energy requirements in this diagram are estimated for stop-and-go city driving using the EPA FTP-75 Test procedure.

Diesel engines have inherently lower losses and are generally one-third more efficient than their gasoline counterparts. Recent advances in diesel technologies and fuels are making diesels more attractive.

Advanced technologies such as variable valve timing and lift (VVT&L), turbocharging, direct fuel injection, and cylinder deactivation can be used to reduce these losses.

In gasoline-powered vehicles, most of the fuel's energy is lost in the engine, primarily as heat. Smaller amounts of energy are lost through engine friction, pumping air into and out of the engine, and combustion inefficiency.

Energy is lost in the transmission and other parts of the driveline. Technologies such as automated manual transmissions (AMTs), double-clutch, lock-up transmissions and continuously variable transmissions (CVTs) can reduce these losses.

Losses from accessories such as electric door locks and signal lights are minuscule, while losses from seat and steering wheel warmers and climate control fans are more significant.

Electrical accessories such as seat and steering wheel warmers, lights, windshield wipers, navigation systems, and entertainment systems require power and lower fuel economy.

The water pump, fuel pump, oil pump, ignition system, and engine control system use energy generated by the engine.

Braking Losses

Any time you use your brakes in a conventional vehicle, energy initially used to overcome inertia and propel the vehicle is lost as heat through friction at the brakes.

Less energy is used to move a lighter vehicle. So less energy is wasted from braking a lighter vehicle. Weight can be reduced by using lightweight materials and lighter-weight technologies. Hybrids, plug-in hybrids, and electric vehicles use regenerative braking to recover some braking energy that would otherwise be lost.

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Wind Resistance (Aerodynamic Drag)

A vehicle expends energy to move air out of the way as it goes down the road—less energy at lower speeds and more as speed increases.

This resistance is directly related to the vehicle's shape and frontal area. Smoother vehicle shapes have already reduced drag significantly, but further reductions of 20%–30% are possible.

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Rolling Resistance

Rolling resistance is a resistive force caused by the deformation of a tire as it rolls on a flat surface.

New tire designs and materials can reduce rolling resistance. For cars, a 5%–7% reduction in rolling resistance increases fuel efficiency by 1%, but these improvements must be balanced against traction, durability, and noise.

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