Slow Down and Save...Gasoline
When I was in high school during the Arab oil crisis of 1973, there was a lot of talk in our civics class about how driving slower was one way to use less gasoline. The next year, the Nixon administration put a national 55-mile-per-hour speed-limit policy in place, and it is credited in part for the decline in gasoline consumption that decade. However, years passed, oil prices fell, the speed limit policy was eased in the late 1980s, and any tie to federal highway funds was completely repealed as one of the first acts of Newt Gingrich's Republican Congress in 1995. Today, I doubt that many drivers think about the connection between speed and gas consumption.
So I was surprised to read in the Congressional Budget Office's recent study on the impact of high gasoline prices the conclusion that pain at the gas pump was causing many motorists to drive more slowly. The researchers looked at uncongested (weekend) freeways in California, where numerous automatic data collection devices have recorded large quantities of traffic data from many locations over long periods. After doing statistical tests to rule out whether the effects were due to seasonal or other factors, the researchers concluded that many drivers did seem to be easing off on the gas pedal. Perhaps a minority of drivers were having an impact, slowing the drivers around them—ever so slightly.
Essentially, the results translated to a 10 percent increase in the price of gasoline causing the median speed to decline by about 0.5 percent. (The slowdown was more pronounced for the slowest drivers on the road and nonexistent for the fastest drivers on the road.) That's saving a little gasoline—less than one-twentieth of a gallon per 100 miles or, as the CBO researchers put it, a teaspoon of gas every 2.6 miles.
But could we do better? The CBO researchers cite a study conducted by Oak Ridge National Laboratory showing that slowing from 70 mph to 65 mph—a 7.1 percent reduction—would cut a typical vehicle's fuel consumption by 8.2 percent. At $3 per gallon, the fuel savings would be worth 9 cents every 10 miles. Travel time would increase by about 4 seconds per mile.
I wonder if drivers think it would be worth it. From a policy standpoint, achieving an 8.2 percent reduction in highway gas consumption without doing a thing to improve cars seems pretty compelling. It's an idea on which politicians have been deafeningly silent. But maybe short of a mandate, there's a way of getting the word out that slowing down makes more sense now than ever. Bully pulpit, anyone?
Tags: cars | gas prices
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What about these hydrogen fuel manuals they sell?
In addition to some other questions I had earlier on drag co-efficient, etc, I'd like to know if these ads about running your car on hydrogen are for real. Is this a scam? If not, why don't we hear more about it?
I know some things.... but I have some questions too.
I know from experience that diesel engines use considerably less fuel at lower speeds due to their high torque at low rpm and drastic loss of torque as rpm is increased. My analogy has always been comparing the long piston stroke to riding a bike in low gear.... you pedal very fast but aren't really getting the work done. Howbeit, I'd appreciate it if someone could expound on that thought.
I've analyzed fuel mileage in my 2001 FORD 7.3 PowerStroke Diesel truck to extreme lengths. I found that the digital readout for current MPG was extremely accurate at all speeds as I compared it with fill up tests on trips of at least 350 miles at various speeds. At 70 mph without using cruise control (cruise causes the accelerator to fluctuate, thus causing lower MPG) this 7800 lb. vehicle gets 19 MPG, at 60 it gets 22 and at 55 I can get 25 MPG. On level ground the best reading was 28 MPG at 43. This was the slowest I could test due to it coming out of O.D. at 42. The digital readout has taught me two important things: Driving slower with the vehicle gives incredible increases in MPG. Secondly, I found that the best MPG was attained by driving with a "dead" foot, in other words, slowing down while going uphill and speeding up going downhill gave much better MPG than maintaining a constant speed. Yes, it's true! Should this also be true with gasoline engines? It's typical that I sometimes get, e.g., 38 MPG going downhill at 80 mph while getting 20 going uphill at 55 mph. Deadfoot driving like this can't be acheived on all terrain though. Most of the time I've had to press down or let up on the accelerator to some extent to maintain reasonable speeds. However, I do try to let my speed fluctuate as much as possible with my somewhat "dead" foot w/o aggravating other drivers too much.
I ran several tests with my Ford explorer 4.0L also. Driving the same trips at 70-75 I got around 23 MPG but when driving as slow as possible w/o getting run over (around 55) I'd get around 28 MPG. The best I ever got with my 5.0L Van was 14 MPG, but when using the "deadfoot" technique I am able to get an unbelievable 17. From my tests I do not currently believe there's a "sweet spot" or definitive speed at which a diesel gets the best MPG, not a reasonable speed anyway, however, I could believe there exists one for gasoline engines due to fact that horsepower rather increases with higher rpms in these engines while horsepower in diesels is higher at lower rpms. As a footnote, I remember my brother showing me how the best times in gasoline drag racing were acheived by running the engine up to around 6000 rpm before shifting (more horsepower at higher rpms). Is it true that the best MPG is acheived at the "best" horsepower? If so, why is this? I'd like for someone who really knows their stuff to expound on this and some of the other thoughts I've shared in my comments here. My guess is that driving slower with diesels yields a much greater difference in MPG than does driving slower with gasoline engines, but I have no idea how much and could only guess that slowing down with a diesel makes twice as much difference as with gas. I do have trouble understanding/believing something that was mentioned earlier. How can wind resistance increase at a greater rate than vehicle speed increase? It would seem to me that doubling speed would create double the resistance on the vehicle. Some really good verification/explanation on my thoughts herein with or w/o the use of some math/physics would be helpful for this layman. Robert
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