In contrast, a lot of traffic jams 'just happen.' The previous sentence is false, strictly speaking; the jams come from somewhere. But you can't point to an individual cause of them; they arise from the local effects of millions of local actions taken by individual drivers.

I've actually seen a study on these types of jams, though I cannot remember the source. The results were pretty simple and surprising. The research discovered they could create a massive traffic jam on a full but still flowing highway by simply having a single car brake for longer than necessary.

The first person would brake for too long, causing the person behind him to brake for slightly longer (he isn't likely to brake for less time than the person ahead of him lest he risk an accident), which continued down the line, a chain reaction. Drivers in the lanes on either side of the initial brake chain would also begin braking as they saw people in the central lane brake, being sensibly cautious during rush hour, which would spread outward from their positions. Eventually traffic would halt, as the people ahead would have to stop completely before being able to move again.

I'm sure there was some kind of cutoff threshold regarding how long over the necessary length of time the first person has to break, but it wasn't very long, a second or two would do it during a non-jammed rush hour.

It also explains why, once a jam occurs for any reason, it is extremely slow to clear up even after the cause of the jam is long since removed.

Pretty shocking really, and certainly not an "emergent phenomena". That's why EY is against using emergence for everything - there absolutely must be a reason, and that reason cannot be "lots of stuff interacts and now we get a traffic jam!" Using emergence as an explanation encourages you to stop thinking about the problem, rather than dig in and figure out why what happened happens.

You have unexplained traffic jams - do you call it emergence or try to explain them? The rational thing to do is to try to explain them in a way that allows you to have expectations about future observations.

In other words, "Emergence" is an answer looking for a problem.