LOL all of the cars are frozen in a giant circle and none of them are moving. They're all detecting each other in a loop around the screen.

Yes, that is called a traffic jam. It happens sometimes during rush hour. Either that or the drivers are too polite to go first! I will work on a 'work-around' on that. But, it will not be that easy.

I would think that not letting them block the intersection would do a huge amount, then resolve a 4 way stop by who ever can go and was waiting the longest.

I made a traffic system found here: http://www.greenfoot.org/scenarios/8256 and I think each intersection had a queue, but also took into account turns and what can go simultaneously through the parts of the intersections

First, I would need a way to determine that a traffic jam exists. But, I do not want to just make them turn to alleviate the problem. I would want them to find a way to continue through regardless (I think the turning would be sort of a cheat and not a work-around). Maybe randomly pick which way should continue first and let all those going that direction through. Then, hopefully, the problem will be cleared up enough for normal procedures.

Maybe I should limit that choice to those direction that lead cars out of the world. That would help clear the central area instead of congesting it.

I do not find the speed bar in the code, so I can not say what is wrong, but if you press and hold the mouse on the xx/70, then it is at 70 and decreases fast to 50.

I was thinking about putting a real time factor in the act method of the speed bar. The speed of the changing of the bar varies as the speed of the scenario changes. However, with the range I gave the bar, quick clicks will produce minimal changes. Maybe better (for changing scenario speeds) would be to only allow single clicks as the range is not that big. I will think about doing that.

I now have an occasional fender-bender at intersections that I need to fix. Just one more check to add. Will work on it in the near future.

Alright, have working code (I believe). Had to re-work the car movement and the intersection pads. Will have documented revision up soon.

The scenario won't load. It says: "NoClassDefFoundError City$1"