Restriction signs are important for road safety. If vehicles hit obstructions due to being too large they can be seriously damaged. If a railway bridge is hit not only is the responsible road vehicle in danger but there is potential major loss of life through the risk of causing a railway accident.
Less dramatically, height restriction signs are important for safety in car parks, loading bays and entrances.
New official regulations came into force on 22 April 2016 that required both metric and imperial units to be used to show width, height and length restrictions. For width and height signs, both imperial and metric units must be shown on the same sign. For length signs, an imperial sign and a metric sign must be shown together. However, existing imperial-only signs, which were installed before 22 April 2016, can remain in place until they become life-expired or are replaced for any reason. These old restriction signs are out of step with modern industry practices. The table below shows the primary metric units in blue, and primary imperial units in yellow.
|Official restriction signs *||feet and inches|
|Private sector signs||metres|
* For old official restriction signs before TSRGD 2016 came into force on 22 April 2016, the primary units are imperial (feet and inches) and the secondary units are metric (metres). In the previous TSRGD, the primary units (feet and inches) were mandatory and the secondary units (metres) were optional.
Britain’s industry was one of the key drivers behind the government announcing its changeover to metric in 1965. With very few exceptions industry uses metric and motor manufacturers are no exception. The vast majority of vehicle handbooks give dimensions exclusively in metric.
Logically it would make sense for road signs to use the same measurement units as motor manufacturers. Sadly that is not yet the case.
New British width, height and length restriction signs
While the vast majority of private-sector restriction signs are exclusively metric, traffic sign regulations require width, height and length warning and prohibition signs to be both imperial and metric. Single dual signs are required for width and height signs and separate metric and imperial signs are required for length signs.
Legacy British width, height and length restriction signs
There will be imperial-only restriction signs for several years until they are all phased out. Until they are replaced, a motorist wanting to know if his vehicle will pass through the width restriction illustrated above will need to use a calculator!
In contrast to road signage, ferry companies require motorists to supply vehicle dimensions in metric when they book.
The above example illustrates this for a ferry journey within the United Kingdom from S.W. Scotland to Northern Ireland. Metric dimensions are required for ferries in the Irish Sea, North Sea and English Channel.
Private sector restriction signage
British industry uses predominantly metric units for designing buildings, for manufacturing and for statutory health and safety measures. It is therefore not surprising that most restrictions for private sector properties, for example for private car parks and loading bays, are given in metric.