The term is "drafting" or "slipstreaming". The concept has been part of the allure of autonomous vehicle engineering for decades, and is already praticed by human truck drivers (though they cannot follow as closely as automated systems would be able to).

I've done it myself in a passenger car on long trips -- once covered most of a state at high speeds behind a truck who seemed bent on making his schedule. 75+ MPH and my fuel consumption was well below typical for that leg of the trip.