How much time do I save when I drive 75-80 mph as opposed to 65-70 mph on a longer trip (over 100 miles)?

Question

I just read an article on saving gas and it claims that you add the equivalent of 20 cents per gallon for each 5 miles per hour you drive over 60 mph. But I'm just wondering what people think about getting to your destination faster to save gas vs. going slower to save gas. On the expressways that I usually drive on for long trips the speed limit is 70 mph and I will usually go as fast as 80mph. Do you think I'm wasting fuel or driving efficiently? FYI: I have a fuel efficient 2-door Civic, use cruise control as often as possible, limit the amount of extra weight in my car, and drive safely. What do you all think?

Answer 1

I tried an experment with my 2004 Dodge Dakota 4X4 crew cab a few weeks ago... On a trip I made, I drove 100 miles at 65 MPH, then filled up the tank and drove another 100 miles at 75 MPH. At 65 I was getting 16 miles to the gallon. At 75 I was getting just over 14 MPG. I'm not a math whiz, and maybe I've got some of this wrong, but it convinced me to slow down a bit on the highway.

Here's the numbers...

100 Miles @ 65 MPH = 1.5 hours
100 miles @ 75 MPH = 1.3 hours

Time lost at lower speed = .2 hours (12 minutes)

100 miles @ 16 MPG = 6.25 gallons
100 miles @ 14 MPG = 7.14 gallons

Fuel saved at lower speed = .89 gallons

Money saved = $2.67 per 100 miles (gasoline at $3.00 per gallon)

Answer 2

Well, it all depends: and what do you mean by: "you add the equivalent of 20 cents per gallon for each 5 miles per hour you drive over 60 mph"? It's not that because you drive fast that your gasoline suddenly becomes expensive- it's that you're using more per mile.

Well, I'm going to assume that you meant: the faster you drive, the more air friction, and therefore more fuel comsumption. If that's the case, don't worry too much about it, the amount of gas you "save" because of driving a couple of miles per hour slower won't give you too much extra money, mabye 2 dollars at most.

It already looks like you're doing your best at saving gas, but there is one more thing you could do to save gas, especially when you are driving on highway speeds: close all of the windows and use the air conditioning. With today's cars, it's more efficient to use the A/C than to open the windows and suffer air friction.

Answer 3

"Do you think I'm wasting fuel?"

Technically you are losing fuel because air resistance increases quadratically with speed. Slowing down to a speed around 55 - 60 mph is the optimal speed range for efficient fuel consumption.

Do you think I'm... driving efficiently?

This question is hard to answer. This question can only be answered by you. You need to place a value on your time.

Assumption:

Travel distance - 80 miles (rural drive)
Travel time @ 80 mph - 1 hr
Trave time @ 60 mph - 1 hr 20 mins
Time saved - 20 mins
Fuel consumed (assuming 35 mpg for less efficient Civic) - 2.3 gallons
Money lost in fuel ($0.20 per gallon per 5 mph over 60 mph) - $1.84

Now is 20 mins saved worth $1.84?

If you place value on time based on your pay rate, then if you make more than $5.50 per hour it may be worth it to drive faster. If you value your time and can find something to do worth more than 1.84 to you in that 20 mins then go ahead and drive at 80 mph. If most cars along the road average 80 mph and you value road safety then keep driving at 80 mph (speed differentials cause a lot of accidents). If you heavily care for the environment (less fuel = less exhaust) and/or want to reduce consumption (and hopefully lower prices) then maybe you should drive at 60 mph.

Therefore my answer is... without more information, the answer is not clear and I hope that the issues I brought you have made the value of the time compared to the fuel consumption clearer.

I hope this cleared it up... or maybe it just confused you more!?!

Answer 4

my f150 ford lightning pick up has a special 351 engine built for these trucks in 93,94 and 95. I get around 15 mpg at 60 and I get around 15mpg at 80. if I have a tail wind I get better and of course a head wind I get worse. I also have a 92 GMC with a 4.3 v 6 & 5 speed tranny. It gets about 24mpg at 60 and about 23 mpg at 80.If I slow to 55 or less both get 3 to 4 miles per gallon better. So if I would drive at 55 I could save quite a bit, but how many of us are going to do that?

Answer 5

Mathmatically, going 80MPH over a 100 mile trip will save you 17 minutes over driving 65MPH. It's not really a whole lot of time saved.
I certainly have noticed a difference in gas mileage since I've slowed down. I used to drive about 75-80MPH on the highways. Now I've slowed down to 67-70 since gas prices have gone up. My car's gas mileage has gone from 28MPG to 31 on long highway trips. Personally I'd say the money saved from slowing down is a much better deal than the time saved from going fast.

Answer 6

75 Mph

Answer 7

You will save a whole 10 minutes. If 10 minutes is worth more to you than the cost of the extra gas or your life then knock yourself out

Answer 8

Assumptions/Inferred Facts:
1. time is more important than fuel.
2.Average higher speed is 77.5mph
3.Average lower speed is 67.5mph
4.Distance=100 miles.
Therefore:
Higher Speed takes 100/77.5 hrs or 1.29 hrs or 77.42 mins.
Lower Speed takes 100/67.5 hrs or 1.48 hrs or 88.89 mins.
On the average, therefore, you will save a total of 88.89 minus 77.42 =11.47 mins (i.e. 11 minutes 28 seconds) over a distance of 100 miles, going at the higher average speed.
Happy motoring!

Answer 9

Ok, take the speed you are driving.
Multiply that by the number of miles you are driving.
Divide by the cost of gas per gallon.
Subtract the speed of the rotation of the Earth.
And finally, add to that the age of your first born male child squared.
The equation should look like this...
S*M/C-R+A*A=answer

Answer 10

depends upon the engine of the car
as you have stated that its a civic their might also be variation according to which years model it is ]
i could clear your doubt if you could give me the engine configuration
otherwise i think a 2-door civic should be more fuel efficient at 80mph