It's a single track design with no fallback. If one of the vehicles has a malfunction with the software it's stuck there and blocks the entire tunnel. Not even

It's a single track design with no fallback. If one of the vehicles has a malfunction with the software it's stuck there and blocks the entire tunnel. Not even staff can get past without climbing over the cars. They have to have a person in the car because if they didn't then it would be a safety disaster in the event of a fire.