Downtown Seattle features an elevated section of highway, known as the Alaskan Way Viaduct. It dates back to the 1950s, and was heavily damaged during the 2001 Nisqually earthquake. There's no question that it's seismically unsound, and our state DoT put out this simulation a few years back to demonstrate what the next big quake is likely to do to it: https://www.youtube.com/watch?v=hos_uIKwC-c

So, a few options were proposed to replace it:

1. Surface highway

2. Cut and cover tunnel

3. Deep bore tunnel

A surface highway is, by far, the simplest option to implement: you knock down the viaduct, and repave the area underneath it (there's already a road under the viaduct—it just needs expansion).

The viaduct is a death trap, and it will kill some or all of the people on it when it comes down. There is absolutely no question about that in my mind whatsoever. For that reason, I absolutely refuse to set foot on it. There's going to be political hell to pay when it collapses and Seattleites are re-reminded that there was no reason why anyone had to die on a highway everyone knew was unsafe.

The area beneath the viaduct would make a horrible freeway. It is, and should be turned into a park with limited vehicle access. There is to much foot traffic in that area. There are better ways to redirect traffic around downtown Seattle without going directly beneath the viaduct

The area beneath the viaduct would make a horrible freeway. It is, and should be turned into a park with limited vehicle access. There is to much foot traffic in that area. There are better ways to redirect traffic around downtown Seattle without going directly beneath the viaduct

In SF, the Loma Prieta earthquake destroyed the Embarcadero highway. It was never rebuilt, but that didn't really cause problems.

The Embarcadero Freeway was not destroyed in the earthquake, although it was damaged. The Cypress Street Viaduct in Oakland collapsed in that earthquake, killing and injuring many people.

Although the Embarcadero Freeway was never rebuilt and that greatly improved the waterfront, a lot of the traffic it carried was rerouted along the Central Freeway/Van Ness (GGB bound traffic) or SOMA surface streets, and no adequate public transit was built either, so "didn't cause problems" is arguable.

The 1989 Loma Prieta quake flattened a similar structure and dozens died horrific deaths. Seattle was content to stare at theirs for nearly 20 years, even after a 2001 earthquake damaged it and the adjoining retaining sea wall.

There was no perfect solution and that got in the way of the good. Most people had the luxury of avoiding using it. I'd summarize the overarching opinion as "suburbanites who thought it would get fixed cheaper and faster once it finally collapsed."