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Idle costs and recompense

December 30, 2014

I’ve written a bit about car ownership, weighing the costs and benefits of renting vs owning for a work trip and the winter/summer difference in gasoline (that latter post being one of my most linked to on this humble blog).  But now that this year’s extended Fall is finally showing signs of winter (snow emergencies announced, wind chill advisories), another topic has popped up; the perceived need to idle/warm up your car (case in point from the Strib/Washington Post).

Now full disclosure, my car is presently sitting in underground parking.  It is wonderful.  I am bourgeois.  Further proof; I just used the word “bourgeois.”  But this wasn’t always the case.  Prior to my last move, I spent the previous 5 years parking my car on the street (and prior to that a mix of garages, parking lots, not having a car, my parents driveway, and again not having a car if we go back far enough).  But I did push my car out of a ditch and a two foot snow drift on my own after a 1am encounter with black ice last winter.  So I’ve got some cred.  I’M NOT SOFT YET!

tailpipeIn any case, I’ve never idled my car to warm it up.  Now I’m not vilifying anyone who does (maybe judging a bit).  But the carburetor was phased out of our cars around 1990, which was the original basis for the concept of warming up your car (mentioned in the article above).  And concepts about oil viscosity seem to disregard the designed operating temperatures of the oil (check the container/rating) and miss the benefit of moderate driving to circulate the oil and better warm up the car after a brief 15-30 initial idle.  So I think we should at least be able to agree that (save those with cars from 1990 or older), any idling beyond 30 seconds is for our own comfort (warm interior, easier to scrape off windows).

So do what you’ll do, but at least know the cost/impact.  Idling your car is clearly a decision you’re making, and decisions are best made based on sound information.  Fortunately, the folks at Argonne National Labs (personally one of my favorite of the national labs) did some awesome analysis (  Note their conclusion that 10 seconds of idling if the cutoff point for when it’s smart to just turn off a warmed up car.

We’ll use their data for an idling car.  One could argue that emissions would actually be higher since you’re basically prolonging how long it takes your car to warm up by letting it sit there rather than starting to moderately drive to your destination.  But we won’t, we’ll keep it simple and go off their test on a 2011 Ford Fusion.  Just note that if you compare some more generic numbers from the EPA for various vehicle types, if you’ve opted for a less “sensible” vehicle than the analyzed 2.5-L, 4-cylinder Fusion, your emissions are greater, ranging from 3-52% depending on the pollutant.

So, the data, what does it tell us.  For every second of idling, the Fusion:

  • uses 0.279 cc of gas
  • produces 0.588 g of CO2

0.279 cc of gas/second * (1 L/1000 cc)(1 gal/3.79 L)(60 sec/min) = 0.0044 gal of gas per minute

So, if you idle your car for 5 minutes to warm it up, you use 0.022 gallons of gas.  Today that’s 4.5¢.  A year ago that would have been 7.3¢.

On the pollution side, we’ll round that up to 0.59g per second to factor in CO emissions (which oxidize in the atmosphere to CO2).  So that’s 35 g per minute and 175 g for 5 minutes of warming up.  Now again I’d point out that this is just climate impacting emissions.  You’ll also be producing NOx, SOx, hydrocarbons, and particulate pollution.  These impact your health directly, the health of others around you, and the environment in different ways.  But I’m not as well versed in the impact calculations there, so we’ll call that the “added bummer” factor and you can ascribe what value you see fit for your neighbor’s kid having a higher likelihood of asthma.

But in all, these are some small numbers.  Like a lot of what we do, it’s easy to dismiss the instances.  Four cents and one third of a pound of carbon emissions, what’s that?  Aggregate it to an average MN winter (which might be hard to remember as we’re coddled this year) and we get about 70 days a year where the max temp doesn’t crack 32°F.  Let’s assume it’s those days, the below freezing days, when our average daily temp is most commonly from a low of 8°F to a high of 24°F, that folks are inclined to idle their cars to warm them up, once in the morning, once in the evening.

That habit then costs you $6.30-$10.22 and causes 54 lbs of CO2 pollution.  Warm up for longer than 5 minutes and you can see how this will escalate.  This also seems like a good time to point out that this is on top of the rest of your costs of driving.  So add it in if you’re doing a cost balance of car use/ownership versus your other options.  And if you have a less efficient car than the Fusion used in the analysis, bump those numbers up.

But let’s say you’re like me and, while you recognize this impact is relatively small/manageable, you still find it annoying and would like to somehow justify it (you know, besides just stopping the bad habit of warming up your car).  I mean, less is less, and small steps are easy, with the end result being drastic change if everyone does their part.  Let’s say the 4.7 million vehicles in MN in 2000 idle once for 5 minutes to warm; that’s $211,500-343,100 wasted and almost 1,000 tons of CO2 pollution.  Why be a part of that?

Tis the season for resolutions, so here’s some ideas;

  • Start carpooling – Sure you probably have to go out of your way a bit, but if the net result is less miles driven, after about 75 miles you’ve offset a 5 minute idling habit.
  • Bike or walk somewhere – Add a layer, embrace winter and head out into it… or just do more of this the rest of the year.  It actually works out to be less miles needed than carpooling because you get a bit of a bonus since short trips are the least efficient in a car.  Rough estimate 60-70 miles walked/biked.

But really, just do something new to save energy and money.  This post is already too long and the list is extensive.  As long as you weren’t doing it before, it counts as an offset, and you’ll be starting 2015 improving your life just that much more.  Check out the EPA or Carbon Fund or countless other places for more ideas.

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