From watching various footage I have worked out how the game decides which ai behaviour to use for junctions. It's very similar to how CIM 2 did it and there are basically three different junction types:
No control: Used by small roads (2 lane, 2 lane one way, dirt roads).
Every direction gets a 'give way' sign. Behaves similar to an American four way stop, except traffic doesn't have to stop if it isn't blocked by another vehicle which arrived at the junction first.
Traffic lights: Used by any junction where two or more of the roads are medium or large roads (4 lane, 6 lane, 6 lane one way).
Every direction gets traffic lights. It appears the traffic lights can adapt their sequence depending on the level of traffic from each direction as they did in CIM 2.
Filter behaviour: Used by junctions where two or more roads are highways (3 or 1 lane). Will override traffic lights if this is the case.
Similar to the no control junctions except vehicles will attempt to merge by adjusting their speed, meaning that traffic should only be forced to stop by particularly bad design or heavy traffic.
Knowing this should help to design a better road system. It means that highways will likely make the best roundabouts due to the merging behaviour. It also means that using two parallel two lane one way roads may be better than one four lane road as you could avoid traffic lights and prevent turns.
It would be really nice if we could choose the junction type rather than it being forced by the road types used though.
No control: Used by small roads (2 lane, 2 lane one way, dirt roads).
Every direction gets a 'give way' sign. Behaves similar to an American four way stop, except traffic doesn't have to stop if it isn't blocked by another vehicle which arrived at the junction first.
Traffic lights: Used by any junction where two or more of the roads are medium or large roads (4 lane, 6 lane, 6 lane one way).
Every direction gets traffic lights. It appears the traffic lights can adapt their sequence depending on the level of traffic from each direction as they did in CIM 2.
Filter behaviour: Used by junctions where two or more roads are highways (3 or 1 lane). Will override traffic lights if this is the case.
Similar to the no control junctions except vehicles will attempt to merge by adjusting their speed, meaning that traffic should only be forced to stop by particularly bad design or heavy traffic.
Knowing this should help to design a better road system. It means that highways will likely make the best roundabouts due to the merging behaviour. It also means that using two parallel two lane one way roads may be better than one four lane road as you could avoid traffic lights and prevent turns.
It would be really nice if we could choose the junction type rather than it being forced by the road types used though.
This is the kind of tweaking I would love to be able to do at least.
