The last time I counted, I have driven in 12 different countries. I found this certainly happens a lot in South Africa and a bit in various parts of Spain and Ireland. It seems to happen a lot less in the UK and Portugal.

Funny you say that about Portugal. I'm Portuguese, and I concur, although I always thought of my opinion as biased.

It does not take many drivers acting responsibly to fix a wave jam. Interestingly, culturally, is that this responsible action is viewed here as a relaxed take on traffic. When the line restarts, some drivers take their time shifting into first gear, and then take a lot of time to increase their speed. They effectively buffer cars behind them from the stop-and-go.

If you get two of these in a row, it's enough for the stop and go effect to dissipate.

If you do this on the road, prepare to be overtaken by someone "in a rush", and prepare to ignore the action, although it's acceptable to gesticulate and swear at the car ahead :-)