The Channel Tunnel is a good example of how it could be done safely. There are two tunnels for trains, and a third smaller tunnel in the middle for emergency use. In the event of a fire people can be (and have been - there have been a few fires) evacuated to the service tunnel, and then road vehicles are sent to collect them.

The Channel Tunnel is only 31.5 miles long vs 230 miles (driving) from New York to DC, but having an access shaft every 30 miles or so wouldn't be that bad.

I'm not sure how you'd deal with the vacuum issue though - I guess doors at regular intervals that can be sealed, so a section of the tunnel can be bought back to atmospheric pressure, and the emergency doors can be opened between the car-tunnel and tunnel-emergency tunnel.

That's precisely my point: with that approach they'd have to dig an parallel 230 mile tunnel just for emergency access. Plus cross passage escape tubes that you can get to on foot before you're overtaken by smoke or gases.

The Gotthard tunnel has them about every half mile, but the Boring Company will use smaller diameter tunnels where smoke and gas spread faster, so they'll probably need them more tightly spaced -- say, every quarter mile. And they'll use separate tunnels for each direction of traffic. So that's three tunnels plus 230 x 4 x 2 = 1,840 cross passage tubes.

This is all technically achievable, but the Boring Company's vision is all about cost.. building tunnels 10X cheaper. This is, I think, at least as great of a challenge as getting government approvals to dig very deep.

You won't get fires if there is nothing that burns.

Wishful thinking. The video envisions Teslas driving directly into the tunnel system via elevators. That means arbitrary cargo and, moreover, Teslas have giant battery packs that can catch fire.

So... passengers can't wear clothing or bring any belongings with them that can burn?

Things you can take on a plane would probably be alright.

But you're accepting passengers and what they carry.