You're working on the assumption that game traffic is a perfect representation of actual traffic. In reality, that's not the case though. In games, traffic on a straight road behaves perfectly. In real life, people cut others off, forget to check their blind spots, play on their phones, etc.
This type of behavior often causes the 'out of nowhere' traffic jams. Someone brakes excessively because of one of the reasons above and people behind them brake even harder. Eventually some people will come to a stop and this will accordion for a while.
No, not in that game. People would cut into each others line all the time and generally behave stupidly. Also, if you have a traffic line where the behavior of the car in the front affects the cars behind it you already have bad traffic, which wouldn't happen with properly designed roads.
This type of behavior often causes the 'out of nowhere' traffic jams. Someone brakes excessively because of one of the reasons above and people behind them brake even harder. Eventually some people will come to a stop and this will accordion for a while.
You can play with this here: https://traffic-simulation.de/
Especially try just disturbing an otherwise nice traffic flow.