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Monday, September 19, 2005

2.70 And Falling

Regular gasoline prices in the Metro Detroit area have drifted down over the last week, from about $3.00/gal to pre-Katrina prices in the neighborhood of $2.60/gal.

What I found amazing was that even when gasoline was selling for $3.15/gal, I still saw lots of people driving their Dodge Durangos, Ford Expeditions, and Chevrolet Avalanches. With no passengers. At 80mph, get the hell out of the way.

For all of the whining that people were doing on the evening news, about how they weren't going to be able to buy as many Christmas presents this year, no one seemed to change their driving habits much. Just slowing down from 75mph to 65mph can give a 10% boost in fuel economy, I have heard*, but people refused to do even that.

Consider: at 65mph, a 15 mile trip will take ~14 minutes. At 75mph, the 15 miles takes 12 minutes.

Would you notice if your drive to work was 2 minutes longer? Most people wouldn't. There is probably at least that much variation day to day based on irregular traffic flow, and variations in when you reach traffic signals.

On the other hand, getting 10% better fuel economy on your morning commute probably isn't that impressive for most people. Assuming 15mpg (the average full-size SUV or maybe a late 90's Chevrolet Impala SS), the difference between 75mph and 65mph might be 0.10 gal, or $0.32 (@ $3.15/gal). Two trips a day for a work-week, and you save one gallon of gas.

20 minutes a week, or $3.15? Which would you rather have?

*Wind resistance increases exponentially with speed.

5 comments:

The Angry Engineer said...

Hey, no picking on the older Chevy Impala SS! My '96 averaged 18-19 MPG back when it was stock (and more like 21-23 MPG on the highway). It's amazing what aerodynamics can do.

Interestingly enough, my truck shows virtually no sensitivity to driving style ('96 GMC K2500). My friend's '03 Chevy K2500 is the same way, despite having the much more modern 6.0L V8 and a manual transmission. Either truck, when driven in just about any fashion, will average 13-13.5 MPG. I haven't been able to figure that one out, but I'm pretty sure it's related to the gearing.

I haven't modified my driving habits lately because I generally don't drive like a jackass during my commute. The route I take to work isn't well-suited to speeding. There's a guy in a WRX STi that often passes me at Mach 3 somewhere near the beginning of my drive, and invariably I catch up to him at a stoplight 10 miles down the road.

Anonymous said...

Likewise, my better half's F-150 gets pretty much the same milage whether he drives it, with plenty of foot-to-the floor acceleration and stab the brakes, or I drive it, with smooth, modest throttle openings and braking, always trying to conserve momentum. Wish we could afford a thrifty commuter vehicle in addition to the truck, which our circumstances requires that we have.

Ray said...

In Houston, they dropped the speed limit from 70 to 55 on roads exending as far as 40 miles out of town in an attempt to control pollution a few years ago. They got virtually zero compliance in spite of a lot of ticket writing.

I would rather use up ALL the gas rather than get run over out there going 55.

Racedriven said...

Hello everybody, just wanted to weigh in on this post, up here in Massachusetts is still $3.00/gal in most areas. My fathers has found better gas mileage on regular and back roads than the Highway and was getting 320 per tank and now 400 mile plus per tank. Interesting on a 2001 Suzuki Grand Vitara. Hopefully prices will continue to go down even more. See Yeah!

automotive breath said...

The angry engineer said
"Either truck, when driven in just about any fashion, will average 13-13.5 MPG. I haven't been able to figure that one out, but I'm pretty sure it's related to the gearing"
Gearing and aerodynamics are only part of the reason. Other differences that are not so well known are the fact the bore to squish percentage was reduced to near 12% in the Trucks; it's likely near 30% in the Impala SS. There's more, the compression ratio in the Impala is near 10:1 the Truck 9:1. The result is thermal efficiency and combustion efficiency goes down along with fuel economy. You have every right to be angry.