From default settings, set speed variance to 50%, launch frequency to 120 cars/minute, and reaction time to 500ms. Unsurprisingly, this is chaos.
Then, keeping those settings, clear the cars and set the target speed to 150km/h. The traffic mostly clears up! Since the cars are going faster, they leave the road sooner, meaning fewer are on the road at a time, fixing most problems.
(Of course, in real life, this also makes the accidents that do occur worse.)
Something this sim doesn't model that plays a large role in real accidents is the speed differentials during merges. If an offramp moves too slowly and gets fully congested, it starts spreading onto the highway, compounding the problem.
Playing Cities: Skylines I've noticed a similar problem when I try to use roundabouts. They're idealized as a way to keep traffic flowing in busy intersections by imposing no stops, but if they surpass a critical mass of congestion, the whole thing stalls, creating a problem worse than stop lights.
(The Cities traffic model is pretty close to how a robocar might behave, as they are polite drivers able to execute apparently dangerous merges with 0% chance of collision, but also have the problem of not detouring when the ideal route becomes congested. As a result, you have to design your city to be decent at diffusing traffic early and not rely on wide roads to do that job.)
Have they fixed the problem where that 'ideal route' even includes not merging left to pass around a stalled lane? It's been seemingly forever since I built a city.
From default settings, set speed variance to 50%, launch frequency to 120 cars/minute, and reaction time to 500ms. Unsurprisingly, this is chaos.
Then, keeping those settings, clear the cars and set the target speed to 150km/h. The traffic mostly clears up! Since the cars are going faster, they leave the road sooner, meaning fewer are on the road at a time, fixing most problems.
(Of course, in real life, this also makes the accidents that do occur worse.)