What’s the hold-up?
Question: On a congested road, why do cars repeatedly stop and start up
again, even though there is no obvious cause for the constant stoppages?
Answer: When cars are following each other along a road, obviously each has
to brake when the vehicle in front does. However, this does not happen
simultaneously. There is a delay of about 2 seconds, because the following
driver does not react immediately. This delay creates the classic conditions for
propagating a wave in the traffic that follows.
When the traffic is free-flowing, there are reasonably large gaps between
vehicles. So when…
