I have noticed this while driving on interstates in a low traffic density areas. Often there will be a group of cars maintaining a similar speed and driving fairly close to each other. Sometime I notice cars following me, sometimes I catch myself following others without deliberately thinking of it.

I could guess a couple of reasons why this happens:

1) Hiding from a speed radar behind other cars. I often see a group form if a fast car passes a group of slower cars, some slower moving vehicle will speed up and follow the leader matching its speed.

2) It is easier to drive if you focus on following something. It defers some decisions (such as choice of speed, lane) to that car. Perhaps it takes less mental energy to follow something than to drive on open road perhaps.

3) Humans are social mammals that like to follow a leader. Such quick groups of leader+followers quickly appear and disappear while traveling on the road just based basic mammal herding behavior.

2,3 might apply to crowds as well.