Traffic jam happens when someone is driving… too fast?

Shanghai interchange

Sometime common sense fails us utterly. How does traffic jam happen? Apart of the obvious reason of having too many cars sharing the road simultaneously, thus causing congestion, we tend to believe traffic jam happens because some people are way too slowly. Imagine my amazement when I read a traffic study about how speeding drivers can cause traffic jam.

When everybody drives at the same speed, there's no traffic jam

Traffic flow is at its smoothest when everybody is traveling at similar speed. Imagine in a situation where everyone is driving at 80km/h. It is not fast, but all cars are moving together. There is no congestion. Imagine a driver who is in a rush. He speeds at 160km/h, cutting left and right in the otherwise smooth-flowing traffic. Because his is moving at a speed much higher than those of other cars, he is bound to make mistakes in maneuvers from time to time. He brakes suddenly. What does that do to the drivers behind him?

They are forced to apply emergency braking too. So do the cars behind them, and the cars behind those cars. That one driver who is in a rush, speeding at 160km/h and braking frequently is disrupting the entire traffic flow. He is causing a chain reaction behind him. Everyone can no longer drive smoothly at 80km/h. Traffic jam begins to form at the far end of the traffic.

It takes but ONE driver to mess up the flow

Let's look at another situation. Everybody is queueing to turn left off the main highway. The left lane on the highway is lined with queueing cars. Now, that guy in a rush wants to jump queue. He wants to cut in AT the off-ramp. Most of us would be mad at his behavior. We would follow the car in front as closely as possible, leaving no room for him to cut in. His behavior is no doubt questionable. But would you believe that allowing him to cut in is the best way to ease the overall traffic?

A one-lane off-ramp is usually wide enough to fit at least 2 cars. According to another traffic study, it is more efficient to allow two cars to enter the off-ramp together, so that more cars can leave the highway sooner, thus reducing traffic congestion.

These are all good theories. Traffic is a sophisticated system with many intertwining factors affecting each other. If every driver can always be knowledgeable and considerate, Malaysia would be the paradise for driving. But people don't think and behave that way. Because, people. Would you give way to the queue jumper? I know I wouldn't.

2021.05 published on ROGER

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Chiew Ruoh Peng

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