You are continuing to make assertions without references. My experience of traffic jams is that they are normally caused by density of traffic. There are a lot

You are continuing to make assertions without references. My experience of traffic jams is that they are normally caused by density of traffic. There are a lot of simulations out there that show how small variance in high density traffic acts like a wave that propagates backwards. You even see it on escalators on the tube here in London, where people are supposed to walk on the left but often get stuck in a standing state at busy rush hour times. http://www.traffic-simulation.de/ring.html http://www.traffic-simulation.de/ring.html is a good one - push up the density and see how the wave propagates backwards. It's not merging that causes the problem, it's density. Of course standstill traffic that stops everything for minutes at a time is usually something else. But that isn't an everyday jam. And everyday jams do make a meaningful difference in transit time. They even affect me on my motorcycle especially as roads get narrower to accommodate bicycle lanes. I do however still get through and it's a rare day that there is any kind of event or interesting artifact at the front of the jam.