Taking I-90 West across the bridges into Seattle every day makes me wonder

I think it’s a technological marvel that not only were bridges constructed to connect Bellevue and Mercer Island into Seattle, but they flow seamlessly into traffic so that you can approach them from I-405 either North or South. Taking this route to work every day has made me curious about some things, so could anybody answer my questions please?

1. At the very beginning, entering from I-405 South into I-90 West, why is there a normal left lane and an HOV right lane? I’ve taken them both to test what happens, and they end up in the exact same place. The HOV lane doesn’t appear to save any time, but it does make you go up a weird ramp that then merges with the normal lane anyway.

2. What’s it like living in one of those houses above the tunnel that says Seattle – Portal to the Pacific? I would imagine they overlook a ton of traffic coming from as far away as potentially Boston, so is it a big deal like a major landmark, or do they think nothing of it?

3. Upon entering the tunnel, you’re suddenly in a scary claustrophobic corridor where signs are posted with the number of feet to the nearest exit door. I assume this is for emergencies like fires, but what’s the point of having the tunnel in the first place instead of just open air? And if you do leave your car and take those exit doors, where do they lead to?