Recently I have started to drive my car slower on the highway in order to save money on gas. However, I feel like I am spending at least as much fuel as before. One possible explanation that I thought of is that now I am decelerating/accelerating more often.

I used drive at a steady 70-75 miles per hour. Now, I try to maintain about 55mph, and because I am more conscious about my speed and look at the speedometer more often, I feel like I bounce more between 50 and 60 mph and do not maintain a constant speed as well as before.

I understand that accelerating often results in a massive loss of fuel, but I believe drag generally increases by the square of the velocity, so going faster takes a lot of power as well.

Regarding aerodynamic information, my car has the shape of a standard pick-up truck.


Simply go by your car's specifications, which is normally somewhere between 50 and 60 miles an hour for optimal mileage per gallon. If your car has, use the cruise control. Unless you press too hard on the gas paddle, keeping between 50 and 60 miles an hour by accelerating on and off mildly should not be a problem. The cruise control also accelerates on and off but keeps it pretty uniform, within a mile or two an hour.

Even without cruise control, you have to do same to keep the car between 70 - 75, as what you have to do to keep it ~55, so that should not matter any way.

Depending upon traffic flow, you may have to use breaks more often if you are going faster, so that also matters. In general more than 65 miles/hour starts becoming inefficient, given all other scenarios are similar.

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