I saw one of these early one Saturday morning on I280 in San Jose. I presume it started with congestion during Friday night commute. It was still there at 7AM - cars adding to the back, slowing to a stop for an instant then starting up again and zooming away from the front. All for no apparent reason (no accident/no other congestion on the freeway anywhere).
The other problem in the Bay Area is that cars don't know how to merge and no one wants to let another driver in front of them.
Packs of 5 or more cars driving close to each other will try to merge in to the freeway with cars on the freeway, who also have little space between them. So eventually everyone needs to brake and it slows everyone else down.
And turn signals are seen as a sign of weakness -- cars will actually speed up to close a gap when you signal.
I saw one of these early one Saturday morning on I280 in San Jose. I presume it started with congestion during Friday night commute. It was still there at 7AM - cars adding to the back, slowing to a stop for an instant then starting up again and zooming away from the front. All for no apparent reason (no accident/no other congestion on the freeway anywhere).