In response to readers’ comments about the legal status of metric units on British roads, Ronnie Cohen has written a summary which he hopes will clarify the situation.
The rules for road traffic signs are governed by the Traffic Signs Regulations and General Directions (TSRGD) 2016. This is the most recent version of the TSRGD. It came into force on 22 April 2016. The TSRGD 2016 allows metric units on the following signs:
|530A||Maximum headroom available at hazard, with height indicated in both metric and imperial units. (On this sign, maximum vehicle height must be shown in metres and in feet and inches.)|
|531.1A||Maximum headroom available at arch bridge ahead. (Two triangular signs with arch bridge images must be shown together, one in metres and the other in feet and inches.)|
|622.1A||Goods vehicles exceeding the maximum gross weight indicated prohibited. (The weight limit for vehicles is shown in tonnes on this circular sign.)|
|626.2A||Vehicles exceeding the maximum gross weight indicated prohibited from crossing the bridge or other structure with exemption for empty vehicles. (MGW is shown in tonnes.)|
|629.1||Vehicles or combinations of vehicles exceeding the length indicated prohibited. (Two circular signs with lorry and length arrow images must be shown together, one in metres and the other in feet and inches.)|
|629A||Vehicles exceeding the width indicated prohibited in both metric and imperial units. (On this sign, maximum vehicle width must be shown in metres and in feet and inches.)|
|629.2A||Vehicles exceeding height indicated prohibited with height indicated in both metric and imperial units. (On this sign, maximum vehicle height must be shown in metres and in feet and inches.)|
|779||“Safe height” and numerals indicating height in imperial units and, in brackets, the height in metric units, with or without “load gauge”.|
|784.1||Drivers of large or slow vehicles must stop and telephone in accordance with the provisions of paragraph 6 of Part 7 before using a level crossing. (This sign shows maximum vehicle height and width in feet and inches followed by metric conversions in brackets, total weight in tonnes and speed limit in miles per hour.)|
|818.4||Nature and location of a prohibition, restriction or requirement with indication of alternative route. (This sign shows a weight restriction in tonnes.)|
|818.5||Location of a low bridge with indication of alternative route. (This shows a height restriction in metric and imperial units.)|
|976||Maximum speed limit for tramcars in kilometres per hour. (This is the only metric speed limit in the TSRGD and is only intended for tram drivers.)|
|2718||Route number and location reference. (This is a driver location sign that shows the motorway, a letter and the number of kilometres from the start of the motorway. Only the number is shown without any unit symbol or abbreviation.)|
|7014.1||Temporary or permanent reduction in bridge headroom ahead.|
|7243||Temporary road layout with lane restrictions. (This shows a width restriction ahead in metric and imperial units.)|
|Lorry symbols showing tonnes are used with other signs to indicate restrictions for goods vehicles over the maximum gross weight shown. No diagram numbers are assigned to them in TSRGD 2016.|
Since at least 1980, motorways have had distance marker posts installed at 100 metre intervals alongside the hard shoulder. These show the distance in kilometres to one decimal place from the start of the motorway .
All distances shown on traffic signs in the TSRGD must be shown in yards, miles or fractions of a mile. There are no exceptions to this rule for any signs in the TSRGD.
All speed limits, except those for tramcars, must be shown in miles per hour. The speed limit for tramcars is shown in kilometres per hour in the TSRGD. This is the only metric speed limit in the TSRGD.
There are just 15 official diagrams in all 547 pages of the TSRGD that allow the use of metric units. For a road traffic sign to be lawful, it must be either prescribed in the Traffic Signs Regulations and General Directions or be authorised by the Secretary of State for Transport. The Secretary of State for Transport can authorise new traffic signs by Statutory Instrument. That is how new metric signs can be introduced on British roads. These new signs would be legal. For example, the new metric social distance signs for pedestrians were authorised in this way.
It is possible for local authorities, private individuals, businesses and organisations to obtain consent under the Town and Country Planning (Control of Advertisement) Regulations to erect signs. All such signs are defined as “advertisements” for the purposes of the Town and Country Planning Acts. Signs conforming to the TSRGD do not require separate consent under the Advertisement Regulations – this has given rise to confusion regarding which signs are “legal” and this confusion has been exploited by those opposed to metric signs in any form. Signs authorised under the Advertisement Regulations can show metric – or indeed any other – units. The Planning Authority cannot refuse consent because of the measurement units which appear on the signs.
Thus it is possible for drivers to come across private signs that show the distance in metres to nearby facilities and exclusively metric height signs at, for example, petrol stations and off-street car parks. These are not official road traffic signs and are therefore governed by the requirements of the Advertisement Regulations, not the TSRGD.
For more information, see the following web pages on the UKMA website:
You can find a copy of TSRGD 2016 in PDF format at https://tsrgd.co.uk/pdf/tsrgd/tsrgd2016.pdf.