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Stop & Start

Hybrid cars are defined by having an electric motor as part of their propulsion system, either as an assist to the gasoline engine (as with the Honda design) or as a separate, lower-speed drivetrain (as with the Toyota and Ford designs). But the electric motor isn't the only element that makes a hybrid efficient. A feature which almost seems like an aside actually accounts for a decent amount of fuel (and emissions) savings: the engine is turned off whenever the vehicle comes to a stop, so there's no sitting and idling. Once the brake pedal is released, the engine comes right back on, with no noticeable delay.

(Although the engine of my Honda Civic Hybrid is quiet, the sudden silence when "auto-stop" kicks in is hard to miss. I've actually had pedestrians tell me that my "car died" while walking in front of me.)

It turns out that the technology for shutting off the engine while stopped does not require the rest of the hybrid system. What's more, alone it can still result in notable improvements in fuel efficiency and emissions reductions. PSA Peugeot Citro├źn has announced its "Stop & Start" technology, which reduces fuel consumption by 15% in heavy traffic, 10% in city driving, and 6% in "combined cycle" use (city and highway driving, where stopping is less common).

Green Car Congress, of course, has the write-up with details and useful (if simple) illustrations from Peugeot about how the system works, from Peugeot's press kit (PDF).

The auto-stop feature is one of two standard hybrid technologies which could result in significant fuel savings if used in non-hybrid vehicles. The other is the mileage readout. Having a real-time indicator of how one's driving affects one's fuel consumption is simultaneously a trigger for competitive, "got to get that number higher" urges and a beautiful example of making the invisible visible. Most people don't know what kind of mileage they get in their cars, or at best assume that the EPA estimates are right (they're not). I know that I've changed my driving habits because of the readout in my hybrid, and anecdotal evidence suggests I'm far from the only one.

Comments (4)

I didn't know that automatic engine shutoff did not require the rest of the hybrid system. For me one of the most depressing sights in the city is seeing masses of cars belching fumes and going nowhere fast.

When idling engines are at their least efficient and if the catalyst element has not reached proper operating temperature the most pollutants are being emitted.

This technology should be required by government making it ubiquitous both saving fuel and reducing emissions.


This is a cool development. Although I usually rant here at World Changing to promote bicycles, my partner and I also own a Civic Hybrid. And I've noticed a definite change in my driving habits due to the goading of the car's mileage meter. For example, I don't punch the accelerator any more and I coast whenever I can. I also find myself getting irritated when ours is the only car not wastefully idling at a stop light.

This is a fascinating study in how the design of a machine can alter the habits of its user. Gas prices, of course, can also alter habits. I've driven around Germany, where gas is the equivalent of $5 or so per gallon, and witnessed many people shutting their cars off at long stop lights and train crossings.

Nonetheless, it would be great if these technologies could be made as cheap, reliable retrofits for the existing fleet.

Monty Zukowski:

Wow, I found an MPG gauge:


But then I read Google's first hit -- http://yarchive.net/car/mpg_gauge.html -- and wonder how that guage could be accurate. It might be helpful, but it's not going to be exact.

That's cool, Monty.

And I wouldn't overly-worry about the accuracy of the gauge, as long as the results are consistent. Even if the numbers are off, it could still tell you which driving practices are more efficient than others.


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