It's bonkers that the US named them but don't require them. They're called Mansfield Bars in the UK too, presumably because there isn't really a better or more descriptive name you can give them.

There's probably an "official" name in some dusty Ministry of Transport document like "side protection collision bar" or some such, and TÜV probably calls it something like "Seitenaufprallschutzgerätüberlaufschutzausrüstung" or some damn thing.