For shipping, there is also an existing concept of sailing slower. Big ports can have huge waiting bottlenecks where the ship just sits at anchor waiting in a queue to be unloaded.
One port is already trialing smarter queueing, where they intentionally tell the incoming cargo ships to slow down a few knots, thus arriving from halfway over the world right at their guaranteed reserved immediate unloading spot.
Slowing down just a few knots seems pretty marginal, but the fuel savings are real – even if the traditional 'cube law' is pretty much an oversimplification and companies already try to find optimum speeds, even a knot shaved off can still bring not insignificant fuel savings.
