Like, the drivers manual? We're talking about basic driving skills here. Cars need room to stop, the higher the speed, the more room they need to stop safely. Most human drivers aren't perfect and leave a lot less room than they should, AVs won't share that flaw.
AVs can react faster than humans - if all the vehicles in the tunnel are controlled automatically, distances could conceivably shortened quite safely. Not sure why "citation needed" was downvoted, it's far from clear no matter where you stand on the issue.