Supplementary plates for warning and restriction signs

Supplementary plates exist below warning and restriction signs to tell you how far a hazard / restriction is. In the UK, the measurements on these plates are either in yards, fractions of a mile, or miles, and need to be converted to either metres or kilometres as appropriate. Conversion of these measurements will be very straightforward. Examples of what converted signs might look like are also shown in this article.

Plates showing the distance to a hazard

Example converted supplementary plates are shown below:

There is no need for any words in the supplementary plate like “Soft verge”, “Slippery road”, “Queues likely”, because the symbols already explain the meaning without any need for words. In fact, getting rid of all superfluous words will save money, especially in Wales where bilingual signs are common). The UK Metric Association have given examples to illustrate the clarity of metric signs here.

Plates showing the length of a hazard

As well as converting to metric, we must use the language independent way of saying “For 4 km” or whatever the length of the hazard is, this is as shown in the examples below:

Note that the plates “For 1500m” and “For 4km” have been shown twice, to demonstrate the possibility of using condensed fonts.

A strategy for converting the measurements

For converting yards, the yards can either be replaced with metres (e.g. 400 yds replaced with 400m), giving an accuracy of at least 90%, alternatively (or in addition) the yard value can be multiplied using a factor of 0.9 (e.g. 220 yds becomes 200m) which could give an even higher accuracy. The important thing is to achieve nice round numbers (divisible by 50 or 100). As well as this, miles get converted to km or m as appropriate, and I recommended that only metres should be used for 3000m (3km) or less.

What some signs might look like after plate conversion

Examples of signs with converted supplementary plates are shown below:

These example hazard warning signs shown above illustrate how the metric versions will be easy to read, and more importantly from a safety perspective, that we also have all the information we need at a glance.

Summary

To summarise, for both types of supplementary plates, metres is expected to be sufficient. For up to 3000m (3km), I recommend that only metres only should be used. For greater than 3km, km can also be permitted. Fractions should be avoided where possible, unless absolutely unavoidable. Either way the conversion of these plates from imperial to metric is trivial, and can be done either with a new plate or plating the existing measurement. The converted signs must be language independent as well.