Idling losses could account for as much as 17.2% of all the losses. In urban driving, this much of energy is lost to idling at stop lights or in the traffic. There are technologies available such as integrated starter / generator (ISG) systems that help to reduce this type of losses. It does this by automatically turning off the engine when a vehicle comes to a stop and restarting it instantly when the accelerator is pressed.

Another very significant loss is through the engine itself. The internal combustion engine of gasoline-powered vehicles is very inefficient. Over 62.4% of the fuel's energy is lost through the engine combustion process of converting the fuel's chemical energy to mechanical energy. Energy is lost to engine friction, pumping of air into and out of the engine, and removing the wasted heat.

Advanced engine technologies have been developed to address these losses. Some of them are: variable valve timing and lift, turbocharging, direct fuel injection, and cylinder deactivation.

Diesel engines are about 30~35% more efficient than gasoline engines. New advances in diesel technologies and fuels are making these vehicles more attractive.

Accessories like air-conditioning, power steering, windshield wipers, and others use the energy generated from the engine. These use up to 2.2% of the energy. Efforts in developing more efficient alternator systems and power steering pumps can improve the fuel economy by up to 1%.

Driveline losses can account for up to 5.6% of the total. The energy is lost through the transmission and other parts of the driveline. To reduce these, technologies such as automatic manual transmission (AMT) and continuously variable transmission (CVT) has been developed.