Originally Posted by RonDawg
It's not legal (certainly not in California where this was filmed) and quite dangerous if you let your speed get out of hand. It's even worse if you tried to control your speed by "riding" the brakes, because if they are overheated, they don't work at all.
From what I've been told on this very forum, on a modern fuel injected car if you downshift in order to control your speed on a downhill run, and don't put your foot on the gas, the engine is using zero fuel and is just one giant air pump powered by gravity, so you're not using any gas whatsoever.
RD is correct. Datalogging has been used to show that modern computer controlled, fuel injected engines use no fuel whatsoever when coasting in gear. Coasting in neutral with the engine running DOES use (some) fuel.
Keep the engine running folks, so that your power brakes and power steering work if/when needed!