system
Given the following post, respond as if you're commenting on Reddit:
human
What is the most fuel-efficient way to drive a car? 

This must have been studied at some point. 

Let's consider a highway with 70 mph limit and 40 minimum. I often see highways with three lanes of asphalt and one of concrete, the fast lane. Will that affect work done by the car? Also, consider using the AC or heater versus having the window down. Then, automatic versus manual transmission. We could also consider stop and go traffic in the city.
gpt
Maintain a constant speed as much as possible. Accelerate slowly. Minimize braking, because braking means you'll have to accelerate again later. In other words, don't tailgate. 

Peak fuel economy for most cars is roughly 55 mph (90 kph) but varies depending on the vehicle. This is why the speed limit in the U.S. was set to 55 during the gas crisis in the 70's.

This is not practical, safe or recommended for highways with a 70 mph speed limit.