Gaper's Block (1964)

[Seán Fitzpatrick]

In Philadelphia, the traffic reporters call it "gapers' delay".

I'm not sure it actually is caused by rubbernecking.  In heavy traffic, even a momentary congestion can linger long after the cause is removed, because cars come into the back of the congested area faster than they can leave the front.  You can also think of it as a wave :  the point at which drivers accelerate out of the congestion propagates back through the line of traffic like a wave.  When the current of traffic is moving at the same speed but in the opposite direction to the wave, the acceleration point stays in one place.  It looks as though drivers are slowing down to look at the accident, but it is more a matter of fluid dynamics than human nature.

Seán Fitzpatrick
Beer is good food
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