eutrophication&hypoxia via Flickr

Gas prices have recently skyrocketed. Not everyone cares about the environmental impact of fossil fuels, but everyone does care about their money. Of all the ways to save gas, nothing can be easier than to reduce engine idling. After all, an idling car still burns fuel and gets zero miles per gallon.

On average, cars use half a gallon of fuel for every hour of idling. That’s gasoline cars. The most fuel-efficient cars use less than that, but if you drive a diesel car, it uses 0.8 gallons of fuel for an hour of idling.

No one lets their car idle for an hour at a time (unless they are in an extraordinarily long drive-thru lane). But all those shorter times of idling add up.

Did you know that the average driver spends almost 60 hours per year idling at stoplights? As I’m writing this paragraph, the average price of a gallon of gas in the US is $3.30. At that rate, we each spend almost $100 every year just idling at stoplights.

Does that still seem like a minor problem? Multiply it by the 250 million or so personal vehicles in the US.

Why is your car idling?

lorenz.markus97 via Flickr

Besides stoplights, we have plenty of reasons—good or otherwise—for our cars to idle.

• Waiting for passengers—especially in places like schools where many other drivers are also waiting
• Waiting in line for a gas pump
• Car washes
• Traffic jams
• Railway crossings
• Sitting in drive-thru lanes.
• Stopping to talk to a pedestrian or someone in another car
• Pulling over to use a smart phone
• Lack of awareness that unnecessary engine idling is harmful

This last point may need some explanation. Back before fuel injection, it was necessary to let a car warm up before starting to drive. Apparently, some people think it still is. Actually, modern engines have an optimum temperature where they operate at their best. A moving car reaches that temperature much more efficiently than an idling car.

A car that hasn’t yet reached its optimum temperature burns gas inefficiently. As a result, it spews more pollutants out the tailpipe than it will when warmed up. Also, an unburnt residue settles on engine parts and causes additional inefficiencies.

In the winter, sometimes people will turn the car on to idle while they scrape ice off the windshield. Certainly a warm car will begin to melt the ice closest to the window and make it easier to scrape. But it can take a long time for the engine to heat up enough to operate the heater. So idling really doesn’t help.

Some people care so much about their own comfort that they turn on the car so the air conditioner or heater can reach a comfortable temperature while they wait inside. And some people leave the car idling while they dash into a store for a quick errand.

Why is car idling bad?

• It’s an invitation to steal the car. Not while you’re in it, of course. But if you leave your car idling in the driveway and go back inside, someone might drive it away. Some people make the local news when they leave the car idling in a parking lot while they shop. Worse than losing the car is losing children they have left in it.
• It’s bad for the environment. Every ten minutes, an idling car spews one pound of carbon dioxide into the atmosphere. This potent greenhouse gas contributes to climate change.
• It’s bad for health. Besides carbon dioxide, exhaust fumes include poisonous carbon monoxide and small solid particles. These pollutants cause asthma, lung cancer, and generally decrease lung function. Long lines of cars waiting to pick up school children are especially harmful to them, because pollutants are most concentrated closest to the ground.
• It’s bad for the car’s engine. A car idling for extended times is operating at less than its most efficient temperature. The fuel doesn’t burn completely. Instead, it leaves behind an engine-damaging residue.
• For all these reasons, it’s illegal in many places. Washington, DC fines drivers $5,000 for idling for three minutes. Idling for a long time is illegal in other cities and in more states than not, although not as expensive.

How can we reduce idling?

One obvious answer is not to drive a gas car.

If you drive a hybrid car and the battery is charged enough, it takes over when you idle. You don’t use any gas at all. And, of course, electric cars don’t use any gas, either. [Idling still discharges the battery.] Newer gasoline cars have the option of an automatic start-stop system. It turns the engine off when you come to a complete stop and restarts when you put your foot on the accelerator.

But there’s no need to go out and buy a new car with any of that expensive innovation. What can you do to reduce idling with the ordinary car you already have?

First, start to drive immediately after you start the engine. So fasten your seatbelt before you start the car. That one little trick doesn’t save much gas at a time, but it adds up.

Second, turn the engine off instead of idling. It’s not true that starting the engine uses more gas than idling. In fact, starting the engine uses less gas than idling for just ten seconds. Starting the engine involves more than just using fuel, so a good rule of thumb is to turn off the engine instead sitting in an idling car for more than thirty seconds.

Now, it’s probably not a good idea to turn it off at a traffic light unless you can correctly anticipate when it will be your turn to go. The few seconds it takes to restart the car can hinder the movement of everyone behind you.

But you can certainly turn the engine off at railroad crossings, in traffic jams, or if you’re in one of those horribly long lines waiting to pick up your kids at school or someone at the airport.

Third, if you must idle, turn the air-conditioning off and roll down the window. At highway speeds, open windows decrease your fuel economy, but when you’re not moving at all, they don’t.

The special menace of drive-thru lanes

Getting zero mpg while breathing car exhaust. Source unknown

About those drive-thru windows, it’s best to avoid them. Banks invented drive-thru lanes to speed up simple banking transactions. Those lines are usually short. If you want to use one, you can easily enough shut off the engine once or twice.

But now, most drive-thru lanes are at fast food restaurants. Those lines of idling cars can get so long that they back up into the street and cause traffic hazards. It takes a long time to get from the back of the line to receiving your food. Park the car. Go inside to order your food.

I know that in the pandemic, some chains have closed their dining rooms and decided to operate drive-thru only. I will be happy to eat there again when they reopen the dining room. Until then, they have forfeited my business. I hope plenty of other people have the same attitude. In fact, for health’s sake, it’s best to cook food at home. Or nuke leftovers. No idling car!

Reducing car idling is only one of several ways to use less gas. They’re all important.