In response to one of his enquiries, the UK Department for Transport (DfT) has provided Ronnie Cohen with an account of recent progress on the introduction of metric signs on UK roads.
I recently asked how the DfT how it decides where to use metric and imperial units. The DfT responded with the general point that “For a traffic sign to be lawful, it must be either prescribed in the Traffic Signs Regulations and General Directions (TSRGD) or be authorised by the Secretary of State for Transport.”. In its response, it also gave a metrication timeline for British road signs:
“1980: Since at least 1980, motorways have had distance marker posts installed at 100 metre intervals alongside the hard shoulder. They show the distance from a pre-defined point on the network measured in kilometres.
1981: In the TSRGD 1981, the basis of controlling the movement of heavy goods vehicles was changed from unladen weight in imperial tons to maximum gross weight in metric tonnes.
1981: In the TSRGD 1981, highway authorities were also given the option of showing metric height, width and length limits in separate signs alongside the imperial ones.
2007: Driver location signs were introduced on major highways at 500 metre intervals. They show the distance from a pre-defined point on the network measured in kilometres.
2016: In the TSRGD 2016, metric units became mandatory for all new signs showing height, width and length restrictions. They must show metres alongside feet and inches.”
This describes the progress that has been made with introducing metric units on UK road signs. Of course, the story begins much earlier, with a recommendation from the UK Metrication Board in 1970 that the changeover to metric units on UK road signs should begin in 1973. Within a year, the Minister of Transport Industries had postponed the matter, and it was stated that “the Government had no alternative date in mind”. Since 1980, as with metrication in other areas, progress has been slow and erratic. However, progress on road signs has been even slower than in other areas of the British economy and very limited progress has been made on metrication in road transport.
British road signs remain generally imperial, leading to a common misconception that the use of metric units for distance on all signs, public and private, is illegal. Britain is probably unique in the world in prohibiting metric units for distance and speed on road traffic signs. Despite the widespread use of metric units on private signs and elsewhere in the British economy, successive governments and the DfT have remained reluctant to consider a comprehensive and orderly changeover. Today’s Queen’s Speech, setting out the current Government’s programme, is unlikely to change this.