[Sohcahtoa82]

Dunno about other states, but in Oregon, it is explicitly forbidden to coast in neutral downhill

https://oregon.public.law/statutes/ors_811.495

> A person commits the offense of unlawful coasting on a downgrade if the person is the driver of a vehicle on a downgrade and the person coasts with the gears or transmission of the motor vehicle in neutral or with the clutch disengaged.

However, this only refers to going downhill. It says nothing about approaching a red light or any other scenario where you might consider choosing to coast.