I’ve walked past this sign many hundreds of times, often feeling a wry smile creeping onto my face at the phrase “invalid carriages”.

It sounds like a relic from a past century, conjoining images that are a hybrid of a sedan chair, a gun carriage and a stretcher. I’ve long wondered why on Earth it would be included on a road sign, and what exactly the sign prohibited.

As so often, it turns out that I was simply ignorant of the law: “The Use of Invalid Carriages on Highways Regulations” were passed well within my lifetime, coming into force in 1989. The term basically refers to things like manual wheelchairs (Class 1), motorised wheelchairs and slow mobility scooters (Class 2), and faster mobility scooters (Class 3).

Intriguingly, it’s perfectly legal to drive Class 2 and 3 invalid carriages—including simple motorised wheelchairs—on a dual carriageway. Good luck with that.

All of them are banned from motorways, though, hence the sign.