Why does traffic congestion occur and what is the first car doing?

[Mary]

When traffic congestion occurs, it is mostly due to accidents ahead or the first car breaking down and being unable to move. Additionally, encountering road repairs or highway construction is also one of the major causes of traffic jams. Under normal driving conditions, even when encountering traffic lights, vehicles do not become excessively congested because the red light lasts at most a little over a minute. Normal traffic flow is not a problem, just slower. More details are as follows: 1. Main causes of highway congestion: Apart from congestion on city roads, highways can also experience traffic jams. Besides accidents or vehicle breakdowns involving the first car, highway construction can cause congestion. The first car must slow down for safety, leading to subsequent vehicles also slowing down, resulting in congestion. 2. Secondary causes of highway congestion: Highways have many ramps, and many vehicles must slow down when entering them. Therefore, when the first car slows down, the following cars also slow down, forcing high-speed vehicles to reduce speed and causing congestion.