I've tried everything I can think of to fix this problem, but I give up now. The delivery place is in the right location, I have no fences, it's not being blocked by anything. The delivery timer will countdown, and then..nothing. They keep driving. I've played for several in game days now, and no luck.
Now the timer won't even begin.
Best Answer
I can see that your delivery area is not in contact with the road. For the moment, prisoners will only leave their trucks if the delivery area is touching the side of the road, otherwise, they go right trough without stopping.
See the second tip here (Beta wiki) and the bug report.