Saul Griffith


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 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.

All right. I’ve been pitching the Long Now Foundation and their Seminars on Long Term Thinking for a while now, and no one is taking the bait. That is, some-number-less-than-three of you have clicked through the links I’ve put up. (WordPress only shows me links that hit three clicks in my stats.) You guys are missing out! These lectures are so good. Imagine, super-smart people giving entertaining, informative talks on their area of expertise and how it relates to long-term thinking. What’s better than that?

I just found out that LNF has video of the seminars up on FORA.tv, in full, for free. I prefer the audio versions, so I can simultaneously clean my kitchen, but if you’ve been holding off because you don’t like podcasts, check them out, in color, along with their slides and footage. Here is a list of all of the videos they have up.

And here are a couple of my current favorites:

Saul Griffith’s “Climate Change Recalculated,” in part about how he very rigorously figured out how much power (in Watts) his lifestyle uses, and then scaled back to his share of global energy production. Really, really good.

Steven Johnson’s “The Long Zoom,” about levels of complexity, cholera, television and video games, the evolution of the detective novel, and why bad ideas stick around, among many other things.

Michael Pollan’s “Deep Agriculture,” about the future of food production.