Why do blinking lights (such as car signals) synchronize briefly over time?

If you’ve ever been in a position where you can see a line of cars in front of you, all using the same left or right turn signal, you’ll notice that most of them will synchronize in blinking for a brief period.

Let’s say there are two cars in front of you (A and B), and both have their left signal blinking. At first, it may seem like A goes on when B goes off, and B goes on when A goes off. Over time, B will appear to “catch up” to A, which shortens the interval between A going off and B going on.

Eventually, A and B will both blink simultaneously in synchronization. Afterwards, B may appear to “slow down” from A, which lengthens the interval between A going off and B going on. Then the cycle repeats itself. You could also interpret this vice versa.

Car signals are just an example. I’ve seen this phenomenon appear in most things that have a fixed pattern.

Does anyone know why this happens? What’s this called?