Ahhh, finally found the YouTube comment that explains why we get traffic waves. Chaos!

“This still wasn’t explained as well as it could have been. The reason the wave spreads is because the cars at the front of the jam accelerate more slowly then the cars at the back of the jam can decelerate by hitting their breaks.

This is partially caused by slower reaction times when accelerating compared to decelerating and partially caused by the fact that all vehicles accelerate less rapidly then they decelerate in the mechanical sense.

The best thing is for people coming up to a jam is to maintain a constant speed that allows them to arrive at the jam just as the last car in it dissipates. “