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Does driving 55 mph help me save gas?


With the high gas prices, I have been wondering if driving 55 mph would help me save gasoline. What is your experience?


With any automotive vehicle I have driven, driving 55 mph would save gas. But what are the implications on driving time?

I will look into 2 scenarios here: the daily commute and a long road trip.

Saving Gas on the Daily Commute

I personally have a long commute to work. 48 miles (77 km) each way. My commute starts with 0.8 mile residential road, then 46.5 miles highway and 0.7 mile slow industrial road. A total of 3 stop lights. About 20 miles of the highway portion are a curvy mountain pass (2 lanes each direction) where the speed limit is 50 mph (80 km/h). The remaining highway portion of my commute has a speed limit of 65 mph (104 km/h).

If I drive during heavy traffic, which means any time between 6am and 9am, and I go with the flow of traffic, then this trip will take me 75 to 80 minutes, assuming there are no accidents.

If I drive off-hours, and maintain 65 mph (which constitutes speeding on the 20 mile stretch where the limit is 50), then I can make it in 55 minutes.

At night with very little traffic I was able to do this 48 mile trip in 44 minutes, driving a Pontiac Firebird. With my Mazda RX-8 I was able to shave off another 2 minutes, bringing it down to 42 minutes.
This meant some serious speeding - think 100 - 120 mph in 65 zones and 100 mph on the mountain pass which is officially limited to 50). In theory, if one drives 100 mph, it should take only 30 minutes. However, even at 1 in the morning, every now and then you will either see a police car parked on the side or some slow drivers blocking all lanes. I have to switch freeways 3 times on each trip, and that's where other drivers always slow me down to something like 40 mph. I may have just gained a full minute by speeding but now, being stuck on the on-ramp, I lose it again.
I used to be pretty bad. I got 4 tickets in 24 months. At that point, I decided to buy a commuter car, a 1992 Ford Festiva (see picture on the left) for $450.
I bought this car because I was tired of getting tickets and having to drive a modern car at less than half of its potential speed. I was tired of being stuck behind slow drivers.
With the Ford Festiva, I rarely find a driver slower than me (they do exist - SUV drivers on cell phones!). As a result, I have a more relaxed drive.

So how much gas does it cost to drive my 96 mile commute? Let's assume a Gallon of gas is $2.50
- Speeding as if I had stolen the car (RX-8):
Fuel economy will be down to 19 mpg then.
96 miles / 19mpg * $2.50 = $12.63
85 minutes (best time)

- Following traffic, in the RX-8 (65 mph)
This car gets about 22 mpg if you drive it like grandma,
basically following flow of traffic and so on.
96 miles / 22mpg * $2.50 = $10.90 to drive to work.
100 minutes travel time.

- Driving 55 mph in the RX-8
Now the RX-8 will get 24 mpg.
96 miles / 24mpg * $2.50 = $10.00.
104 minutes travel time.

- Using the commuter beater car (Ford Festiva).
Average fuel economy in that vehicle with manual 5sp transmission
is 44 mpg, at speeds between 55 and 65 mph.
96 miles / 44mpg * $2.50 = $5.45
104 minutes travel time.
(Note: the travel times are estimates. Obviously one does not drive on a perfect track but has to vary speeds)

So the savings in gasoline are not to significant. Driving 55 mph instead of 65 will not cost you much time. It would save me 90 cents a day. Probably there are other savings for example less wear on the brakes and tires.

Is it worth it to speed at all? Not when you look at the numbers. Certainly it gives some thrill and satisfaction to just fly by SUVs or overly heavy muscle cars (think: Trans Am, Ford Mustang GT) that have to slow down in curves, but it saves 13 minutes. Assuming that you did not get caught by the cops and you did not get into an accident which in my opinion is more likely if you speed like that - how will you make use of those 13 minutes? Will you turn on the TV and watch commercials?

I have concluded that it is best for me to drive the Ford Festiva with its measly 63 hp engine - saves me about $5 in gasoline and its tires are a lot cheaper also. In fact the whole car cost me less than 2 tires on my sports car.

Saving Gas on the Long Road Trip

Last month I drove to Las Vegas. That's a distance of 530 miles from the San Francisco Bay Area (where I live). I could've done this trip in the little gas saver car - at 44 mpg I would have paid $60 in gas money. (1060 / 44 * 2.50 = $60)
I chose the RX-8 instead and paid a little over $120 in gas money.

Yes, on a long road trip with decent traffic situations, you can save serious time if you speed.
It took me 7h to drive to Vegas (with some breaks included). In the Festiva it would probably have been 9h. I was willing to pay $60 more to save 2 hours of my time in each direction.

Generated 20:00:39 on Sep 25, 2020