TECH: Your Next Car Will Have Auto Start/Stop, Like it or Not

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Auto Start Stop BMW

Automakers are desperately trying to make cars more fuel efficient. This is partly due to consumer demand and partly due to increasingly stringent government standards. Automatic start/stop technology is one of the ways they hope to meet those needs.

Current regulations call for a 54.5 mpg fleet-wide fuel efficiency rating by 2025. This is a big challenge for automakers. Assuming nothing changes, it means that from 2012 to 2025 fuel efficiency standards will almost double in the US.

This is great for the environment and it’s great for consumers who will pay less for gas, but it’s not great for automakers. They have to come up with technologies to eke out every last ounce of fuel efficiency, and one of the technologies that has taken root is automatic start/stop.


It works by activating every time you hit the brakes and bring the car to a stop. Once the car stops, the electronics in the car turn off the spark to the ignition and the fuel flow to the cylinders to shut off the engine.

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It’s just the engine that turns off, so you’ll still have your heat, air conditioning, and radio even with the engine off. The instant you lift your foot off the brake, the engine restarts with the help of the starter motor and you’re ready to go.

Ideally, the transitions as the engine turns off and on are seamless and happen so quickly that no one even notices. The reality is very different.

Some cars do this so smoothly that you really won’t notice unless you’re paying attention. The only indicator of what’s going on is that things get very quiet, which will surprise you the first time it happens. Especially if you have a manual transmission, the silence will make you think you stalled the car.

Unfortunately, in many cars, automatic start/stop is very noticeable. The sound of the transition is jarring and it even jerks the car, almost like you just gave the brakes a quick tap. It’s not pleasant and in heavy traffic, it’s downright annoying.

You can turn off the feature in most cars, which defeats the whole purpose of having it in the first place, but it’s easier to live without than endure those rough transitions.

The gas savings is between 3% and 10%, so auto start/stop makes a big difference. That is, however, a pretty big range, which shows how unpredictable real-world results can be with this technology.

If you drive through rush hour traffic where your car is constantly stopping, then you’re going to fall near the high end of that range. If you mostly cruise the highway and don’t have to stop as often, then your gas savings are going to be lower.

Despite the variable fuel savings and awkward transitions that take away from the driving experience, that looming 54.5 mpg fuel efficiency rating means the technology is here to stay.

Looking for a new or used car? Check out BestRide’s listing search here.