Translation:In the traffic playground, children learn traffic rules.
In the Czech Rep. it is literally a playground for children to go (usually on bikes) and learn traffic regulations. It's quite a good thing, in my opinion!
We had this discussion on a translators group a while back and concluded that there's not one term for it in English like there is in Czech. That park in Southampton calls theirs a "cycling training track" so it's probably meant for kids learning to pass their cycling proficiency tests. A wider one for cars could be a driving training track / training area.
I think "traffic playground" is a bit confusing because the word traffic usually means "provoz" rather than "doprava".
See the comment from pbiegaj1 on this page. It is certainly not a driving school!
I have seen the very same thing (a playground with intersections, traffic signs and zebra crossings) even in the UK.