I do lots of gliding in nuetral since my area is difficult to actually shut the engine off. This drops the rpm from a normal driving range to your idle range which reduces the amount of gas used. Actually shut off is best becuase it uses NO gas but this creates some "problems" like (in my car) loss of power brakes, loss of running lights and low beams, and the fact you have to start it back up which my car doesn't like drift starting too much for some reason.
I do however actually shut the car off going down steady inclinesfor 1.6 miles every morning on my way to work/school, and 2.1 if I go to a nearby town, and either 2.2 or 4.9 returning to my town.
Whatever fits your terrain..
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