I think the most rewarding solution to the problem would be the implementation of one-way roads, ramps, elevated roads, overpasses, underpasses – so that we the players have to think how to solve traffic jams ourselves. I’d definitely be willing to pay for a such a DLC or an expansion themed around roads and road networks.
At the moment, this is one the few features that the competition (CiM2) is better at than Train Fever.