A big reason (this is from the project site):

> NEPA Completed 04/12/2018: Finding of No Significant Impact (FONSI), Liberty Canyon Wildlife Habitat Connectivity Project

> In compliance with CEQA, Caltrans held a 47-day public scoping period to allow the public and regulatory agencies an opportunity to comment on the scope of the IS/EA and to identify issues that should be addressed in the environmental document. A scoping report documents the issues and concerns expressed during the public scoping meetings held on January 14, 2016 and the written comments received from the public, community organizations, and governmental agencies during the public scoping period from December 14, 2015 through January 29, 2016. The release of the Final Environmental Document with responses to comments included was completed in the summer of 2016. NEPA/CEQA was completed in April 2018. A total of 8,859 comments were received in response to the draft Environmental Document, with only 15 opposed.

When any infrastructure project requires nearly a decade of preliminary work before shovels hit ground, said work becomes impossible to accomplish for smaller-scale builds. Even if ten smaller bridges would be a better solution, 10x-ing the review process would likely be impossible at current staffing / budget levels.

It's a big problem.

If it's too small/unsafe you'll end up with wildlife not using it or being funneled in for other for predators. The larger and more skittish the animals you want to use it, the larger you're going to want to make it. Since they're calling out mountain lions, which are quite skittish, they're going to need a large (and probably partially covered) pathway for them to want to use it--as opposed to treating the freeway like the barrier it is to wildlife.

I'm sure there's more to it than that, but making it desirable, accessible, and for it to feel safe for the target animal population is important for it to accomplish what it's intended to do.

There are smaller culverts all over the place for smaller wildlife. I've even seen some called out in small walking paths--there for the frogs and other amphibians.

Morbidly curious, I'd love to see a full cost and time breakdown of these projects to understand exactly where the $100M and 3 years goes. How much of that is actual people wearing boots and hardhats, and how much of it is paperwork, and waiting for this inspector to inspect that thing and then unblock this other bureaucrat to stamp onto that other paper. I'd bet the actual amount of time and money spent actually building was a single digit percentage vs. the amount of time and money spent on process and paperwork and waiting for clerks to go through their 1,000 item backlog of forms to fill out and stamp.

Bridge in earthquake zone vs an intersection is a great comparison!

A bridge for deer isn't any easier to build than a bridge for pedestrians, even if you don't care about deer being on a bridge that collapses there's a highway underneath. Cars would be crushed and traffic disrupted. So we're just talking about a bridge. It's built to the same standard as any other bridge. (Also it's more like a bridge for mountain lions but whatever.)

If the Empire State Building had been built across a highway, and had to schedule construction around avoiding disruptions to traffic, than it would've taken three years too.

We went faster when human life had less value. It has more value now, both in labor time (and therefore cost) and harm potential/reduction, so it takes more time and money than it used to. Similar story about disposable workers when the Hoover Dam was built.

We should expect this math to continue as prime working age cohort shrinks over the next century due to structural demographics.

For deer? It's much more for the endangered wild life like mountain lions. I loved in so cal and we had multiple passes like this and it was incredibly helpful in maintaining the mountain lion population

5 people died constructing the Empire State Building.

0 people died constructing this bridge.

I guess if you think working class people's lives aren't important then the human cost doesn't matter to you, but for non-sociopaths it does matter.