A quick heads up on the “cars getting stuck (in each other)” situation.
I looked at several save games (thanks to everybody for sending them in!) and the cause for the traffic jam is not the cars that get stuck in each other, as some of you suggested (in some cases cars can spawn into an existing jam but would drive on normally when there is way for them to go).
In the most cases it is in fact a grid look caused by 2 cars, who want to turn at the same time. Like in the screenshot above, the blue car might want to turn to south and the white one to the north and now block each other.
However trams getting stuck at stops is a different topic. I have put both topics on the list of problems which are urgent to resolve.