[hypeatei]

Who's entering the signal that the runway is locked? What if they screw up?

There are so many failure modes with vehicles and planes using the same tarmac that I fail to see how anything would be worth developing here that doesn't eliminate that requirement altogether.

[renewiltord]

Currently it’s automated at this airport: https://www.faa.gov/air_traffic/technology/rwsl

Presumably this is lack of familiarity with this on the part of firefighters.

[hypeatei]

Ah, okay. I suppose it'll be part of the investigation but I wonder if the RELs were indiciating an unsafe runway which prompted the firetruck to ask or if they always ask for permission. Either way, I think my assesment is still correct: there are a lot of edge cases that neither lights nor humans are going to stop. O'Hare apparently has tunnels/underpasses for ground vehicles to use which seems basically foolproof for avoiding collisions like this.

[red_admiral]

No-one goes on a runway without positive ATC clearance, even emergency vehicles.

In Germany at least, if the runway access is "red" then the only thing that lets you cross the lights is an explicit ATC command to cross the reds as well as general clearance, and that's part of training and procedures because it's a semi-automated backup system to the human primary system. RED MEANS STOP is drilled into everyone precisely to reduce the number of runway incursions/collisions.