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Possible big fuel and emissions saver?

Do you turn your engine off when waiting for a train to pass? What about a red light that you just missed and know from experience will take several minutes to go green again? Would you do it more often if you always knew exactly how long you were going to sit before getting the green?



I’ve got an idea for getting you this information without adding any infrastructure. It would only require some reprogramming. Most traffic signals are computer controlled nowadays. Why couldn’t the DOT make the yellow light flash very briefly every five seconds during the red phase whenever there was more than a minute left? Then it could flash every two and a half seconds, until there were only ten seconds left, at which point it would flash every second. The red would of course remain continously red the entire time. Implementing this idea would cost almost nothing (in transportation spending terms) and require no changes in basic traffic laws or conventions, but could save unimaginable amounts of fuel and hugely reduce emmissions and CO2. Best of all, there would be no new rules or big brother. It would force nothing on anyone!



When I learned to drive, they taught us that is was wasteful to idle for more than three minutes. On modern cars it is more like ten or fifteen seconds. Not everyone believes this, and many people refuse to ever turn off their engine when they are in their car for any reason, but there are plenty of people out there who are with the idea of saving money, reducing emissions, or both. Enough anyway, that this would have a significant impact from the outset. With a big public awareness campaign (Which could be privately funded) participation would grow quickly, the positive results would become documentable, and many naysayers would jump on board too.



I’m sorry I can’t provide documentation on gallons of gas or tons of CO2 saved, but I’m convinced it would be well worth doing. If you feel the same way, please help. Lets get some numbers together, and start writing our legislators!

Update. A good fact sheet from the Environmental Defense Fund can be viewed here:
http://www.edf.org/documents/9236_Idling_Nowhere_2009.pdf
Note. You don’t need to be an environmentalist to like this idea. You only need to like money!

It’s my understanding that shutting off the engine while waiting at lights, etc, is common practice in much of Europe, where fuel is very expensive.

I’ve started shutting off the engine in my vehicles when I know I won’t be moving again right away. I’m not doing it at every light, but if I’m stuck in a traffic jam and nothing is moving I shut it off. Same thing at a drive-up ATM. Turn it off.

It may not save much, but every drop matters.

Some will claim the extra wear and tear on the starter outweighs the savings. I’m not worried about that right now, because, as I said, I’m not turning off the engine every two minutes. Just when I know it’s going to be a while before I can move the vehicle, and safety is not compromised by having the engine shut off.

Wear and tear on the starter and ignition switch is the downside.

As I recall, some years ago the Ohio State Patrol did a study of that and found that the trade off point was about five minutes. Less than five minutes (that is more than most lights) it cost more in wear than fuel saved. I would guess that is still about right today.

Most, if not all, hybrid cars do just that, but they have special starter motors and batteries. They also don’t have the problem of starting off when the light changes as they can get moving using the big batteries until the engine is running again.

I should add that if you are driving a diesel, they idle much more efficiently than gasoline cars, so they would require an even longer idle time to break even.

Also consider the extra wear of all that starting.

Finally remember that most gasoline cars pollute the most (per unit of fuel consumed) when idling. I just don’t recall how much more.

When you add it all up, I is not really a good idea.

How about reteaching the driving public on how to drive? Every time there’s a red light and I coast up to it anticipating for a green, people would pass just to stop in front of me. Hurry up and wait. When the light turns green, I gotta wait for them to get going again.

Touching the brakes and idling at a stop waste energy. The former wastes a lot more. Keeping cars going saves a lot more energy than shutting off engines. I like the idea of red light duration signal. But using the signal to keep cars going as long as possible should be the goal. Another problem is safety. Emergency services have to wait for people to restart their engines. Also, are you going to bail if a garbage truck with no brakes is heading for you? Or you’re going to try a restart?

As it is now traffic signals cofuse people, any addition to the basic red,yellow green is too much information for the general public to process.

“As I recall, some years ago the Ohio State Patrol did a study of that and found that the trade off point was about five minutes. Less than five minutes (that is more than most lights) it cost more in wear than fuel saved. I would guess that is still about right today.”

Five minutes seems implausible. The EPA and many other groups say ten seconds. And don’t forget that you are reducing wear by running your engine less. Yes you might burn your starter sooner, but other engine components might last longer.

“Most, if not all, hybrid cars do just that…”

Yes, and the break-even time for diesels is longer, but the overwhelming majority of passenger vehicles in the US run on gas.

“Finally remember that most gasoline cars pollute the most (per unit of fuel consumed) when idling. I just don’t recall how much more.”

?? Yes, but that supports my argument. When idling, you are getting 0 mpg, and in fact doing nothing but polluting. We should try to idle less!

“…Another problem is safety. Emergency services have to wait for people to restart their engines. Also, are you going to bail if a garbage truck with no brakes is heading for you? Or you’re going to try a restart?”

Well, emergency vehicles can be heard from a long way off. You will have plenty of time to restart. As for the garbage truck, such events are exceedingly rare, and you probably would have better chances escaping on foot anyway. But, participation is voluntary. People will always find obscure reasons why they need to idle, but 100% compliance is not necessary for this to have a huge positive effect! Even those who don’t take part will enjoy cleaner air and maybe cheaper gas!

Please, everyone read the EDF report linked above!

Oh, and I forgot:

“As it is now traffic signals cofuse people, any addition to the basic red,yellow green is too much information for the general public to process.”

I really don’t think this is true. I’m sure police hear excuses to this effect all the time, but the reason people don’t obey signals is not because they don’t understand them.

I think shutting off the motor to save gas is a good idea at times. Where the “break even” point is on a modern computer controlled fuel injected car would be nice to see documented.

As for the stop light idea, interesting. Yet, in Boston years ago it was the local habit to start when the stop signal went to “yellow” for the other traffic. They liked to get a head start on the green. If you were a newbie to this Boston habit you’d get either honked at or rear ended if you didn’t start up just prior to your light turning green. This experience leads me to say that driver’s would misused the info on the traffic light and start to “jump the green”. This will lead to more accidents and less safety at stop light controlled intersections.

robo2071, I appreciate that your heart’s in the right place, but I’d disagree with promoting engine shut-down in driving lanes.

First, alerting motorists whenever there’s “more than a minute [of red light] left” only works for lights on a timer. Most modern lights are triggered by sensors that detect the metal of a waiting car, so the wait time is unknowable. (I.e. if I stop at a “smart” red light, I wait until there’s a break in cross traffic…however long that might be.) These sorts of lights reduce idling and delay of traffic as it is, and it seems doubtful that going “backwards” in technology will reduce net idling, especially as participation is voluntary.

Second, starting a vehicle is generally done with “extra” gas, per the ECU. This is why mileage contests using the “pulse and glide” technique “bump-start” the vehicle when it’s time to end the “glide” and begin the “pulse.” In addition to momentarily increasing fuel usage, a rich start will pollute more HC and CO.

Finaly, in a real-world application, plenty of vehicles are in less-than-pristine condition, and cannot be relied on to start quickly each and every time. This delays (and increases the idling of) every vehicle behind the car that cannot start up again promptly. Considering that this technique would be most desirable to those struggling to afford fuel (and thus likely to be too poor to own a pristine vehicle), aggregate idling might be increased, not decreased by such a measure, even if the individual in question does somewhat better.

It would add wear and tear to the starter. Cars that automatically shut off the engine when you are stopped (like hybrids) have special starters that can take increased use. Until all cars have these special starters, this would lead to premature starter failure.

Yes, I shut off for trains and traffic signals if I know the red signal will be long.

Better would be count-down signals, which I saw in China.

RED: 69, 68, 67, … 3, 2, 1, then it changes to GREEN: 50, 49, 48, 47,…

You know you will not make a green signal nearing zero, so you start coasting.

You turn off the engine and restart when RED gets to 3, 2, 1, 0.

I try to read our new count down walk signals.
That allows me to start coasting early when I know I will not make the green signal.

I think shutting of the engine while waiting for a train to pass is not a bad idea, but most stop lights, at least where I live, don’t last long enough to do so. I would rather buy a little more gas than replace the starter or ignition switch. Also, I think a car polutes more on startup than when idling.