The BBC reports that London mayor Boris Johnson is planning changes to the iconic road-crossing symbol. Once, both signs and usability were very similar in a huge range of countries, and in the UK you grow up learning that ‘a little green man’ means ‘walk’, and a red man means ‘walk only if you fancy getting run over’. (Of course, some countries have alternate crossing icons, including the USA, which unfortunately often favours using English—walk/don’t walk—in favour of language-independent icons.)

In recent years, I’ve noticed a surprising and disappointing trend towards diversity. When Fleet high street (Fleet being the town in Hampshire where I live) was revamped, so were the crossings. Rather than looking across the road at the ‘icons’ to see whether it is safe to cross, you now have to look towards the symbol on the same side of the road as you. I’m sure someone somewhere surmised that this was a more logical thing to do, but convention has long been otherwise, and I’ve watched people in my town—particularly young children—struggle with this upheaval.

In London, Johnson is planning on taking things further, replacing the standard icons with a countdown timer, primarily to hurry people across the road. However, with existing iconography so ingrained and clear, there’s a massive danger that pedestrians will have to revert to assumption when it comes to safely crossing. In general design, such as icons on websites, assumption is never a good thing and can hamper usability. But in road systems, it’s downright dangerous.