[always-open]

If you put a modern ICE car in neutral while moving, you’ll use as much gas as you would while sitting in a parking lot idling. However if you just coast in gear with the engine braking slowing you down, a modern car will turn off the fuel to the engine, so zero gas is used.

[sokoloff]

Then you trade greater pumping losses (reducing kinetic energy of the car) in exchange for lesser potential energy (gasoline) usage. It's not a free lunch.

[kube-system]

Yes, but driving a vehicle is not a steady state problem. When a driver lifts the throttle, the next action is typically an intentional demand for a loss of potential energy (i.e. the driver is moving their foot to the brake)