efficiency


My wife Reanna was ambivalent about owning her first car, largely for reasons of environmental ethics. So when she got one she started reading about “hypermilers,” a group of people developing driving techniques to increase gas mileage in their vehicles.

I’ve been interested, of course–this is right up my alley–but have little time for reading these days. Here is the only hypermiling post I’ve read,which is quite good. Mr. Money Mustache, a financial blogger, monitors his miles per gallon, gallons per hour, and other information like engine temperature in real time while he drives. He uses a bunch of driving techniques, and averages 44 MPG in his Scion (rated at 27 MPG) in city driving. Some highlights from the article:

“‘If you have to brake, you’ve made a mistake’…. [P]retend [your brakes] are hooked up to a speaker on your dashboard which blares out my voice saying ‘MEEEEEEEHHHHHHHHHH!!!’ at you for the duration of your brake application….”

When you decide to drive 75 MPH, sing this song in your head: “I am Mister Fancy, I am in a hurry, my time is so valuable that I am wasting gas. Wasting gas, wasting gas, look out world I’m wasting gas. Tomorrow I will save some gas, but today I’m wasting gas”.

On the use of air conditioning: “Is it dollar-an-hour hot in here today, or not?”

Reanna started tracking her by-the-tank gas mileage right away, using Gas Cubby, so we have a record of the MPG for every tank of gas we’ve put in. Lately I’ve been driving it the most, so I decided on an experiment based on Saul Griffith’s (which I wrote a bit about and linked to here):  I drove a full tank with an self-imposed speed limit of 60 MPH and then a tank at 55 MPH max. There are 65 and 60 MPH speed limits posted for parts of my normal commutes, so these new limits affected a significant amount of my driving–maybe a third? So to be clear, I drove normally for me (which does not include hypermiling techniques, for the most part) unless the posted limit was above my imposed new limit, when I would drive at that speed.

Hack display of 29 tanks in our 2-door Toyota Yaris. The X axis is MPG.

Sorry about the hack display, but I think it gets the point across. Each dot is a tank and bigger dots mean more tanks at that MPG. The tank with a 55 MPH speed limit was the least efficient driving, at 32.5 MPG and the tank with a 60 MPH speed limit was the most efficient, at 40.8 MPG. I really did not expect this. I expected 55 to be more efficient than 60 and I did not expect a limit of 60 to make much of a difference.

Some complications to consider: 1) It is winter right now, and we are not using air conditioning, while many of these tanks supplied energy for significant AC use. And colder engines are less efficient. 2) I was not perfect and exceeded by self-imposed speed limits accidentally, off and on. Also, I drove 10-15 minutes of my 55 MPH tank at posted speed limits of 60 and 65 because I had something time-sensitive to deal with while my mom was in the hospital. 3) Reanna drove the Yaris 25-30% of these tanks, and she is a congenitally slow driver, rarely exceeding 55 MPH.

And a note about the psychology of driving slower than a posted speed limit: I was surprised at how embarrassed and defensive I felt while driving slowly on the highway. It breaks a social norm that I didn’t often notice: Driving slower than a posted speed limit is deviant. You will drive as fast as you are allowed, if not faster. It reminded me of when, because of a back injury while a student at the University of Oregon, I started standing in the back of the class during lectures. I realized that no one stands during lectures or meetings, and it really sticks out when someone does, regardless of how harmful sitting is.

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I’ve been visiting Vancouver for a few weeks and most days we end up commuting at least once from the west side of the city to the east side and back, mostly by car, sometimes by bus. (I’ve done it by bike, too, but not on this trip.)

It’s about six or seven miles each way and takes about 30 minutes. Google maps says 20 minutes by car, and I’ve heard rumors of 15-minute trips, but I’ve yet to experience one less than 30. Yesterday, our commute was 10 miles and it took 50 minutes (extra Christmas shopping traffic, I’m told). That’s five miles per hour in the middle of the day. It was worse on the way home, at 3:30 rush hour.

I found myself quite impatient with this situation. Five miles an hour does not seem a reasonable speed to travel. I think of Los Angeles as congested, but in non-rush-hour traffic I expect to be able to get to another city in 20 minutes–from the train station in Los Angeles to my brother’s house in Glendale, for example.

The thing is, I’d be on the I-5 most of that trip. There are freeways all over the place in LA. This is strikingly not the case in Vancouver. We are on surface streets wherever we go, hitting stoplight after stoplight, very often with no left-turn lanes so traffic piles up behind each turner. Suddenly I miss all of those ugly, loud LA freeways.

Reanna and her family argue that the fact that it sucks to drive in Vancouver is an accomplishment. The more it sucks to drive, the better, because more people will use public transportation or bicycle. We fought to keep freeways out of here, they say. I was reminded of how upset my grandfather gets when he talks about the freeways in LA. The house he built was one of the houses they demolished to put in a freeway (it might have even been the I-5 that went through his house). Freeways went through the middle of neighborhoods, loud and ugly, splitting them in two. It’s very hard to imagine that happening in Vancouver, if only because the real estate is too expensive.

I am pro-public transportation, so when I’m not stuck in Vancouver traffic I think it’s a shame that LA was designed for cars. Maybe it is the relative ease of car-travel that has kept LA’s public transportation from moving to the next level — though LA, at least according to this article, is quite low in miles of freeway per person compared to other major US cities.

This situation does not strike me as a straightforward win for Vancouver, though. People still drive a lot, and in cars constantly in their least efficient mode, stopping and starting all the time. The busses use the same congested, no-left-turn-lanes roads as the cars, so they lose efficiency and speed along with them. Maybe the answer is to have the government quadruple gas prices or insurance prices to make driving a rich-person-only thing, and leave the roads for public transit. I’d much rather see public transportation that wins because of how great it is, rather than because of how crappy driving has become, but I guess I would take what I could get. Not that I could get quadrupling the price of anything related to driving even here in the most progressive part of Canada. That might be less popular than putting in freeways.

In thinking about all this, I wanted to be able to compare the transportation systems in different cities and found it quite difficult to do. We need a single-number transportation index that takes into account the average speed of travel, average energy-expenditure per mile, and how far people travel on average to live their lives in their area. People-miles per gallon-minutes, maybe, or maybe people-kilometers per joule-minute. Any economics or urban planning students out there looking for a project?

I heard a segment recently on NPR about gas prices and it reminded me of the link between driving speed and gas mileage. According to the story, driving over 60 miles per hour is equivalent to paying $.25 more per gallon for each five miles an hour faster. So if you paid$4.00 for a gallon of gas, but burn it at 65 miles an hour, it’s like having paid $4.25. Seventy miles an hour makes it $4.50, etc.

It seems funny that it’s very easy to imagine Americans complaining about the price of gas, but very difficult to imagine them driving the slightest bit slower in order to save that same money. In fact, I can easily imagine an American burning a 70-mile-per-hour gallon of gas to go out of their way to save $.25 cents per gallon at the pump. (It could be a good economic decision to do so, I suppose, depending on how many gallons of gas you need to buy, and how much your time is worth, but it still seems funny.)

If I remember my physics correctly, I think the loss of efficiency is actually not that linear, that a 75-mile-per-hour gallon probably costs significantly more than the $4.75 that NPR’s equation predicts. It has to do with the amount of force each particle of air hits the front of our car with–it’s the same principle we (if we are from the desert) use to remember to drive slowly or stop during a sandstorm, to save our windshields from getting sandblasted. Any physicists in the audience care to explain the mechanics of it?

In his excellent lecture “Climate Change Recalculated,” engineer Saul Griffith tells about how he gave an intern this incredibly boring job: Drive his wife’s Honda Insight in 100 mile stretches around a runway at constant speeds, twelve 5-mile-per-hour increments from 20 to 75 miles per hour. Seventy-five miles per hour was the worst, obviously, at about 40 miles per gallon, and the most efficient speed, at about 85 miles per gallon, was 30 miles per hour.

That’s pretty slow, but three times as fast as the average driving speed for large urban areas, he points out. I’ve been thinking about making my next trip to Portland at 30 miles an hour, to see how little gas I can use to get there. It’ll take 4 hours to get there, so I’d better bring some good company.

In a part of the new Seminar About Long Term Thinking, “Deep Optimism,” Matt Ridley talks about the ethics of buying local. Apparently, the amount of fuel used to ship an object to a store in the US from a factory in China is on average ten times smaller than the fuel you use to drive to the store to buy it. There are other factors in the ethics of buying local, of course, but it may be that how you get to the store is a more important decision than how far away the object you want was made or grown. It makes me wonder where buying mail-order falls in terms of fuel efficiency. Will we see Amazon asking us to buy from them to protect the planet?

I kept track of my driving mileage this last year here, and my biking mileage here. I drove (that is, I was the driver of a vehicle) for 5,056.1 miles and bought 152.341 gallons of gasoline. I bicycled 837.52 miles during the same year, almost entirely in just-under-two-mile-each-way commutes to school.

That means, according to the .28 calories per mile per pound of body weight calculation suggested by this site, I burned about 31,658 calories of food by biking this year. That’s about 1,266 medium-sized carrots, or 220 beers. And, according to this site, that is approximately the same number of  calories that are in a gallon of gasoline, so I bought 152 times as much calories of gas to drive my 5,056 miles as I did food energy to bike 837 miles. That makes biking a heck of a lot more efficient! My driving calories could have gotten me about 125,000 miles on a bicycle.

I’d like to do a cost analysis, too, but I’m behind on updating Quicken. Maybe later.