1Two things about every driver
A tiny wait, and a gap
To see how a jam is born, you only need two everyday ideas. Watch each one move:
The tiny wait
You don't brake at the exact same instant. When the car ahead slows, your eyes see it, then a beat later your foot moves. That little wait matters.
The gap
The space you leave to the car ahead. A larger gap can give a driver more room to slow gently. A small gap leaves less room to respond.
2How a slowdown gets passed back
Pass it on harder, or pass it on softer
When one car slows, every car behind has to slow too. The only question is whether each one slows a little more or a little less than the car ahead. Here are the two cases:
Pass it on harder
Cars are close, so each driver brakes a touch harder to feel safe. The slowdown can grow as it travels back.
Pass it on softer
Cars have room, so each driver can ease off a touch softer. The slowdown can shrink as it travels back.
3Your turn — drive the ring road
A circle of cars, going round and round
This model always has 18 cars on the same road with the same starting gaps and speed. The slider changes only how many cars use a shorter reaction wait. A white roof marks each short-wait car. Without a disturbance, watch them keep flowing.
Average motion: smooth
4One change for the whole road?
Can one quicker reaction protect the whole circle?
One car has a shorter reaction wait; the other 17 still wait longer. All use the same braking rule and start equally spaced. Give a different car one brief brake tap. Is the one short-wait car enough to keep this model flowing?
Guess before you poke it
After one brake tap, what happens with just one short-wait car among 17 long-wait cars?
White roofs mark short-wait cars. Changing the count resets the same starting road. These are model waits, not measured human reaction times.
Road status: flowing