The RAC is calling on the government to update guidance, making clear where and how yellow boxes should be used.

Roads are a devolved issue in Wales, meaning they are overseen by the Welsh government.

Rod Dennis of the RAC said: “We fear that unnecessary penalties are going to mushroom in the coming years as more councils start enforcing yellow boxes, unless a responsible approach to the design and enforcement of them is taken.”

In Cardiff, the fine for being caught in the box is £70, reduced to £35 if paid within 21 days.

It is the same rate in England, outside of London, but on TfL red routes – which carry 30% of the city’s traffic – the fine is £160, reduced to £80 if paid within 14 days.

The penalty is £130, reduced to £65 if paid within 14 days, on roads managed by London boroughs.

Mr Wright said even “a car bumper overhanging part of a box” could result in a fine.

“Yet in so many cases, drivers can’t avoid stopping in them – a good example being where a yellow box is so big that a driver can’t see where it ends,” he said.