That compares to about 22 percent in 2015, Navigant says.
Currently, hybrids employ stop-start technology, but it's becoming increasingly common on a diverse array of conventional vehicles, as well. Examples include some 2015 models of the Audi A6, Chevrolet Impala, Chrysler 200, Ford F-150 pickup, Mazda 6, Jeep Cherokee, Porsche Macan and Volkswagen Golf.
So, is it worth it?
Stop-start systems save fuel and reduce emissions by automatically shutting down the engine, rather than idling, when a vehicle stops, and then restarting it when the driver presses down on the accelerator.
"The basic stop-start system is gradually evolving into one piece of a multifaceted approach to improving fuel economy in light-duty vehicles," said David Alexander, senior research analyst with Navigant Research, in a statement. "This is spurring the development and implementation of ancillary systems, such as air conditioning, power steering and brake assistance."
One reason for the increased development is that stop-start isn't the same as simply turning off your engine at a stop light. Many vehicle systems need to be added or altered for it to work smoothly, and components must be upgraded to handle extra loads.
One obvious example is the starter motor, which has to be more robust. Stop-start technology also requires a heavy-duty battery, not only to meet the demands of the constantly cycling starter, but also to keep items like lights, fans, windshield wipers and radios functioning when the engine shuts off.
And, not surprisingly, the whole system is computer-controlled, requiring additional software, sensors and other high-tech equipment.
According to recent real-world testing by Edmunds, the technology can be expected to deliver about a 10 percent improvement in fuel economy, depending on where you live and how you drive. For example, said Dan Edmunds, director of vehicle testing, "people who live in particularly tough traffic areas with long wait times could do even better."
For the test, Edmunds used a modified version of its Orange County, California, test loop, eliminating long stretches that lacked stops. The resulting 80.4-mile loop took about three hours to complete, and each vehicle was put through its paces twice on succeeding days, once with the stop-start system on and once with it off.
Models tested were from Edmunds' long-term test fleet: 2014 Mini Cooper (1.5-liter turbocharged three-cylinder), 2014 BMW 328i GT (2.0-liter turbocharged four-cylinder) and 2015 Jaguar F-Type R (5.0-liter supercharged V8).
Edmunds says: Stop-start technology provides one more way for manufacturers to deliver better fuel economy to consumers and meet emissions requirements, and if Navigant is right, we'll have to get used to it.