Restriction signs
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.
Official regulations for restriction signs are out of step with modern industry
practices. This is summarised in the table below with metric units in yellow and
imperial in turquoise.
| Information |
Primary unit |
Secondary unit |
| Vehicle dimensions |
millimetres |
|
| Official restriction signs |
feet and inches |
metres |
| Private sector signs |
metres |
|
Vehicle dimensions
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.
British width, height and length restrictions
In contrast to industry practice for vehicle dimensions, traffic sign regulations
require width, height & length warning and prohibition signs to be imperial.
Additional metric dimensions in the form of a dual or separate sign are
optional.
A motorist wanting to know if his vehicle will pass through the width restriction
illustrated above will need to use a calculator!
Ferry information
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.
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