Electric cars may be all the rage, but for now, all but a tiny fraction of the 250 million vehicles on U.S. roads burn gasoline or diesel fuel.
One of the ways that new vehicles are boosting fuel efficiency is the use of what are called "start-stop" systems, which switch off the engine while the car is stopped.
Now, as the Department of Energy pointed out Sunday in its Fact of the Week, the number of those systems nearly doubled last year on light trucks sold in the U.S.
They were fitted to 10.4 percent of the light trucks sold during 2016, but that proportion all but doubled to 20.3 percent for 2017.
The "light truck" category includes crossover utility vehicles and SUVs (a segment whose sales have surged in recent years) as well as minivans and pickup trucks.
The comparable start-stop system numbers for passenger cars (sedans, hatchbacks, and wagons) were 9.1 percent for 2016 and 14.2 percent for 2017.
Mercedes-Benz integrated starter generator (ISG)
The full data comes from the January 2018 update to the EPA's Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends: 1975 Through 2017.
Originally used on smaller engines and powered only by beefy 12-volt batteries, such systems are now getting more capable and more complex.
The arrival of 48-volt enhanced start-stop systems allows engines to stay off longer, and accessories like air conditioning and audio systems to keep operating longer as well.
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As defined in the report, a "start-stop" system is non-hybrid, which is to say the system cannot provide any motive power to the drive wheels.
That contrasts with mild-hybrid systems like those used by Honda (in multiple generations of its Integrated Motor Assist system from 2000 through 2016) and General Motors in its Belt-Alternator-Starter and eAssist systems.
Start-stop systems have been all but standard in Europe for several years now, and they provide a greater boost in fuel economy and reduction in emissions on EU test cycles, which have more urban stop-and-go driving.
Ford Auto Start-Stop fact sheet
The Environmental Protection Agency estimates that a start-stop system in the U.S. can boost fuel economy up to 4 or 5 percent, depending on where and how the car is driven.
Such systems also depend on weather, as they will activate less and for shorter periods when weather is below 40 degrees F or thereabouts.
Industry analysts anticipate start-stop systems will be used on more vehicles in years to come, and say they may become largely standard equipment by 2020 or later.