Citybound - The Road to Alpha, Week 10 - Enter the Spaghetti (http://blog.cityboundsim.com/the-road-to-alpha-week-10-enter-the-spaghetti/)
I've been following the progress of Citybound, a new city simulation game being built by a single developer. Yesterday, he posted a video update that showed new road mechanics, including the ability to add lanes to roads and split them off into interchanges.
Even without the actual city-building, I think this would make a great visualization tool for interchange concepts (aka the Fictional Highways section can switch from Paint to something pleasing to look at).
This looks like it could be the SimCity 4 successor we've been waiting for all these years.