[Xylakant]

I don‘t think it‘s as trivial. I‘m definitely no wildlife expert, but the wildlife crossing that are built over here are wide bridges with a lot of greenery growing on it, so that it feels more like a small hill with a tunnel through it. And I‘d assume that there‘s reasons to build them that way - other than „all wildlife experts agree that it‘s more beautiful.“ I can imagine that some species of wildlife just don‘t crawl through culverts - or even may not fit. Can you imagine a deer getting on it‘s knees and squeeze through, antlers and all? I can‘t.

[WalterBright]

Culverts come in all sizes, even 10 foot diameter ones.

The problem with throwing $90 million dollars to build one is you cannot build very many at those prices. That means that predators will know they can hang around them picking off any herbivores that try to cross.

Culverts of various sizes can be placed - animals come in various sizes.

[saagarjha]

It's good to be curious on Hacker News, but I have to ask if you have experience in this area or are just saying things that sound reasonable to you? Despite not being an expert, I happened to hear the opposite a while back, and doing a little bit of research seems to agree that predators do not actually do this: https://www.nature.com/articles/s41598-020-67340-8. I understand the concern of "why could this possibly take $90 million, the animals don't care anyways" but I am sure that more thought has been put into this than just sticking corrugated metal culverts every so often.

[WalterBright]

The bit about predators hanging around the only access across a highway I saw in a documentary. Mountain lions would hang around under a bridge over a stream. It's the same reason predators hang around water holes, etc. They aren't stupid.

> I am sure that more thought has been put into this

I am not. Sometimes it takes someone outside the industry to see the obvious. And besides, SpaceX figured out how to launch rockets at what, 10% of the cost of NASA?

I saw a documentary once on one of those zillion dollar animal crossings, and the activists and designers simply went ape over it like they were building the Taj Mahal.

Highways are built over culverts all the time. They know how to do it. It doesn't cost $100,000,000 to do it. They don't even have to raise the highway - the highway is often raised up already on a berm of dirt to keep it from flooding.

[WalterBright]

My dad in the AF once saw that engineers devised an elaborate draining system so a highway could be built across a swamp. He suggested instead they bulldoze a berm and build the highway on that.

That reduced the cost by about 95%, and they adopted it.

Note that the civil engineers working on it all failed to see the simpler, vastly cheaper option.

[saagarjha]

Yes, it happens, and we love to see it here when it does. But I'm not sure that really qualifies what appears to be musings as anything beyond that.