Monday, February 7, 2011

Everytime you take a short trip, a kitten dies. And you lose a lot of money.

So you love cruising around town. It's quality fun, no doubt, especially in the warmer weather, driving around, radio blasting Billy Joel (or Creed, or Lady Gaga, or Stravinsky - whatever floats your boat). Nothing like jumping around from store to store during the week, going to the gas station to get gas, heading to the grocery store several times a week to pick up a meal for the evening, or driving down the street to drop something off to a friend cause it's quick and easy.

The zooming around town for every little errand is part of the American culture that stemmed from years and years of gas costing less than water (sort of like wine to the French). The thing is, the prices are creeping up once again, slowly but surely, and these habits from the days of sub-dollar gas prices are costing us.

The general rule is this:

Do not take short trips in your car(!).

Cars get their worst possible mileage in the first five to ten minutes of driving. In the winter, this time is prolonged and the mileage becomes atrocious during the warmup phase. To stop for errands, wait until your car is fully warmed up, and then stop for whatever you need on the way home instead of just after leaving the house. Go for broke on those grocery trips, get what you need for a week. Driving your car three miles on a cold engine, especially in winter, will absolutely kill your mileage. Even in my Prius, I know from my house to the grocery store from a cold start gets me about 20 mpg. If you think you're safe with a 25 mpg average EPA rating car, you're probably getting 10-15 mpg during the first few minutes of cold weather (sitting at the stop light is 0 mpg, by the way!).

Let's do some actual calculations. Let's say you can get 30 mpg in your vehicle (very generous, the US average is below this). You expect to go 240 miles between fillups for a grand total of 8 gallons. My most recent gas price of $3.18/gallon would give us $25.44 for a fillup. Let's assume 1,200 miles a month for a total of five fillups in a given month, for a total of $127.20.

Now let's say that you drive a mere 30 out of those 240 miles on short-distance trips - to the grocery store, etc. At 15 mpg your mileage will instantly drop to 26.66 mpg for the entire tank of gas. You've lost over 11.1% of your mileage, and you're paying 12.5% more at the pump. That monthly gas bill jumps to $143.10.

Let's double that amount to 60 miles of short driving per 240 mile fillup. It sounds like a lot, but if you kept track for a week you would find a whole host of surprise short trips that add up. Bank, grocery store, post office, little shopping trip, gas station, dropping off something at someone's place (cause moving a couple thousand pounds of steel is reasonable to transport a piece of paper...go for your e-mail!) - it's easy to do.

With 60 of your 240 miles at 15 mpg, you now drop to 24 mpg, a drop of 20% from your original figure of 30 mpg, and you pay an whopping 25% more! For what other good or service would you pay 25% more than what you need to besides gas? The premium is enormous. You now pay $159 a month instead of the original $127. It's the equivalent of filling up your tank an entire extra time per month!

For the extra you spent, of course, that adds up into $381.60 over the course of the year. Seems better to save it than to spend it for no reason...

So what's the solution? Besides stopping only after the car is warmed up for errands and doing a lot of grocery shopping instead of a little, don't forget that bikes and your own feet get infinite miles per gallon. Walk up the street to the drugstore. Ride your bike to the post office. It's fun, more relaxing than driving, good for you, and costs you and the environment nothing.


  1. Dear Mike with a Prius,

    I love your blog and your driving advice, and I want to make sure I'm comprehending it fully. I'm going to pose two hypotheticals, and I would like you to tell me if they are different, and if so, which one would be better for mileage:

    (1) You stop for an errand on your way to work
    (2) You stop for an errand on your way home from work

    I know you say above that it is better to stop on the way home, but I just wanted to make sure I understand why. In both scenarios above, the distance is exactly the same. The only difference is the point at which you stop your engine -- either at the beginning of the trip before going a longer distance, or at the end of a trip after having traveled a longer distance.

    So, I guess my larger question would be: does it matter when you stop your engine if the hypothetical distance is the same no matter what? In other words, when you turn your engine off to run an errand on the way home, as you suggest above, does your car retain some of the "warm-up-ness" from when it traveled the longer distance, or do you have to start fresh every time you restart your engine?

  2. Dear Jason,

    Thank you for your well-written, thoroughly thought out comment requesting clarity on my previous statements. Your cogent reasoning and careful yet zazzy writing style are befitting of a future Harvard or perhaps BC doctoral student, I would wager :-)

    The idea is that the engine should be warmed up. This can take basically no time in the summer, but can take a good solid 5-10 minutes in colder weather. Poor Wentworth wouldn't even glide tonight (engine off) in this 19°F weather until maybe 12 minutes into the ride (though FYI I somehow eeked out 61.9 mpg display).

    It's true that on the way home versus to work is actually irrelevant. I sort of assumed many people do their convenience shopping at drug stores and grocery stores close to home, so it makes sense to stop at those places on the way back from a longer trip instead of just after leaving the house heading somewhere else.

    Your first assumption about retaining "warm-up-ness" is absolutely correct, and the crux of the whole thing. When possible try to stop for errands when you've been out driving for awhile, and not a couple minutes after starting the car, be it from work or home.

  3. Dear Mike with a Prius,

    You are simply too generous, but your kind words are certainly appreciated, as are your offerings of clarity and clear, direct answers to my many questions.

    I think you are quite right that people do most of their convenience shopping close to home. And it is very helpful to know that your car will stay warmed up when turned off for short periods of time after a longer trip.

    In that line of thought, it seems like it would also be advantageous to do all of your convenience shopping at once, even if it involves multiple stops and multiple instances of turning the car off, rather than doing one-off shopping trips here and there. Not only does it probably save you time in the end, but so, it would seem, does it save you gas money!