Some people are unconsciously always accelerating slightly as long as the road ahead of them is oprn. Then when they catch up to the traffic ahead of them they have to step on the brakes.
Brakes waste fuel every time you use them. They turn the energy you used to accelerate or maintain the cars speed into heat. Drive smoothly and try to flow with traffic. I drive a 2012 4 cylinder Camry and easily get the 35 mpg highway rating using a top speed of 75. Of course I have driven a few million miles.