Have been built over the past 20 years, I remember one of the first was built on Bozeman Pass in Montana, project spearheaded by the Craighead Institute.

There are several in northern NV as well on US93 north or Wells, NV.

Yes they do save lives of wildlife and people and their vehicles. Totally worth the investment.

As of January, over 200 underpasses, overpasses and fencing structures have been put in place.

Here's Planet Wild's video about their part of the initiative:

hitting an elk at speed makes a helluva mess.