> Ventilating well enough to cope with electric motors sounds much less demanding than coping with having both combusion engines and humans in the tunnel.
You will always have humans in the tunnel. How do you plan to perform inspections, maintenance, and even emergency support when a cart breaks down and blocks your tunnel?
The acceptable conditions for "workers in the tunnel performing regular maintenance" and "a continuous stream of random people" are pretty different. Probably >10x less requirement for fresh air when >100x fewer people are breathing it. Ambient humidity might be lower, and even if it isn't the temperature only has to be workable rather than comfortable or at ambient. Worst case, you could shut everything down and let it cool off before sending people in.
Certain emergencies would also be much easier to handle without people, like nitrogen purging a fire. Realistically I don't think you'd want to shut down the whole tunnel and wait for hours when you need to fix a problem, but it might work if there aren't many problems. It might work for routine maintenance if it's utilized like most packing facilities- deliveries go out in waves, with packing etc in between.
You will always have humans in the tunnel. How do you plan to perform inspections, maintenance, and even emergency support when a cart breaks down and blocks your tunnel?