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Comment by tines | Hacker News Reader

I heard somewhere that the reason is to provide trucks the ability to shed speed to make these sharp turns, and then give them back their speed when coming back down so they don’t have to brake hard or spend a lot of gas to do it.

Basically lets trucks use gravity to store their energy when making sharp turns and then get it back for nearly free.

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Another couple aspects of the high-5 not mentioned in the video:

-it doesn't have any lane merges, you can change from one highway to another without merging, your bridge just becomes a new lane on the next road

-these bridges are very long leading up to the turn, so it displaces a lot of traffic and shifts a lot of the lane changing upstream.

Now THAT is some cool engineering I can get behind.

That sounds like tens of millions in extra infrastructure costs so as to save trucks a tiny amount of gas.

It is Texas, so anything is possible.

It’s Texas so you would assume they want people to waste gas.

I thought they wanted to sell it to other states

Never understood when major exporters of $thing would also specifically heavily subsidize $thing

Organic advertising? As in, showing prospective importers how cool it is to have abundance of $thing.

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 https://www.fhwa.dot.gov/modiv/programs/intersta/docs/interc... I see the short comment

> 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.

But that's the main thing I can find right now.

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.

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.

Does anyone have a link to something that supports this theory?

Those steep ramps and banked curves sure are fun when an ice storm comes along about once every five years.

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