Tens of millions in extra infrastructure costs to save a lot of trucks tiny amount of gas per ride, over many rides per year, over decades? That's literally what infrastructure is meant for.
Infrastructure maintenance is far cheaper in areas without regular freeze/thaw cycles (like most of Texas). I wouldn't be surprised if almost all road spending in southern states went straight to highways and ignored local roads though, as there are a ton of dirt roads unless you are in a city or on the highway.
I've never heard of the proposed gravity assist theory in any discussion of these interchanges. Does it happen? Sure. Is it one of the reasons behind the design or just something that happens to also be true is the actual question. Pontificating on the interwebs is fun
> At service interchanges it is desirable to design the interchanges with the crossroad above the freeway due to:
> - The crossroad above the freeway results in longer sight distances to the exit ramp and gore area.
> - The crossroad above the freeway allows gravity to assist the operation of both accelerating vehicles (the on-ramp has a down-grade) and decelerating vehicles (the off-ramp has an up-grade). In addition, the resulting grades generally provide longer sight distances.
Energy savings isn't the point though. The point is so that large trucks won't slow down traffic having lost a bunch of energy from braking to get on a cloverleaf.
