When I first started driving I drove slow bc I thought it would save gas, then I started driving faster when a friend told me you use the same amount of gas whether you drive slow or fast (as long as it’s the same distance), you just would be driving fast for a shorter amt of time and driving slow for a longer amt of time, but at the end you burner thru the same amount of gas. Is this true?
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The fuel efficiency do depend on the speed. It is in large part because the air resistance is proportional to the square of the speed. To stop air resistance from slowing you down is the main thing the engine do when you drive at a constant speed.
According to [https://afdc.energy.gov/conserve/behavior_techniques.html](https://afdc.energy.gov/conserve/behavior_techniques.html) the fuel efficiency drops rapidly and see the fuel efficiency also increase at very low speed. you can look at the worst case of you idel the car where fuel it used to keep the engine running and generate electricity but there is no motion. So a speed of 0 is the worst.
That said it is not efficient to go very slow because eighter. You can look at a graph like [like this](https://www.researchgate.net/profile/Sara-Hernandez/publication/261948625/figure/fig3/AS:286636043718656@1445350766029/Speed-fuel-consumption-curves-for-gasoline-passenger-car-by-engine-technology.png) and see the fuel efficiency also increase at very low speed. It looks to me that the min of the graph is at 65km/h but isis quite flat from 50km/h to 80km/h.
The exact number will depend on the car. If your car has a function to show current fuel usage that will be in liter/100km or miles per gallon. If it is liter/100km it should be as low as possible but as high as possible for miles per gallon. That value a fule usage compared to the distance not fuel usage per unit of time. So any effect of it taking longer to drive there is included in the value
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