On a highway that could cause an accident as traffic behind the self driving car would have to screech to a stop or swerve around. There needs to be some way to get it to pull over onto the shoulder.
This highlights a meta-problem of highways in general: they're very high-speed conduits, which are not intended for traffic to whiplash to 0 MPH in a short distance, where accidents and emergencies can definitely create roadblocks that force traffic to whiplash to 0 MPH over a short distance.
It'd be nice to have a solution to that. There are no inexpensive ones (rails handle this with corridor control... Every N miles, a signal indicates whether it's safe to proceed to the next segment. Some sections of highway have signage allowing for this; most don't).
I've always wanted to run a traffic simulation to see if traffic is eliminated if the highway was partitioned (5-10 rows of car per partition) into several chunks going at a precise speed and requiring cars to maintain some distance between the next partitions behind them. This could be accomplished with some tracking laser following the cars against the wall. Of course this would be ruined as soon as drivers wanted to hop into the partition in front of them, change lanes, etc.
Another slightly relevant idea is to mark intersections with a large red no-go area placed at the calculated point, where, if you were going the speed limit, if the traffic signal changed to yellow and you were in this box you could not safely pass the stop line. I hate having to guess how long a yellow light is (3 to 6 seconds is a large gap).
If you can't slow down in time to avoid hitting the car in front of you when it slows down, you're tailgating, and are a danger to yourself and the cars around you.
The problem isn't when you're tailgating, the problem is when you're comfortably cruising at 80 mph and all of a sudden you realize there's a stopped car in your lane. It can be surprisingly hard to notice the one car that isn't going with the flow of traffic. There are videos of cars getting totaled this way. Not sure I want to know what happened to the passengers.
On busy highways, if your car breaks down and you need to slow, one of your biggest concerns should be to get out of the way asap before someone rear-ends you.
Whether you consider it a result of tailgating or not, pile-ups are a common result of unexpected action on a highway.
I haven't hit anyone so far, but I've gotten rear-ended myself. Twice. Thankfully never been stranded on on a highway like this.. https://www.youtube.com/watch?v=2lnYOlUnsWI
