As noted in a comment on our last article, the BBC’s acclaimed new series Blue Planet 2 uses metric measures for smaller distances and depths but miles for greater ones. Ronnie Cohen takes this opportunity to look at instances when kilometres are preferred to miles.
In the UK, miles are generally preferred to kilometres, especially in the non-specialist media. This is probably a consequence of the continued use of miles on road traffic signs, and contrasts with the widespread use of metric measures for shorter distances. However, we are accustomed to using the kilometre in many different contexts in the UK, and this article looks at some of them.
These have been metric for as long as most people can remember. Although the Olympic Games have used metric units since their foundation in 1896, the Commonwealth Games did not adopt metric measures until 1970. The official distance of the marathon is 42.195 km.
Marathon and charity races
Such long-distance races are often advertised as 5K and 10K races. There often seems to be a reluctance to use the symbol for the kilometre – km.
Football (soccer) commentaries
I have occasionally been surprised when Match of the Day has shown the number of kilometres a footballer has run in a game among the statistics. English football remains Imperial, but the rights to broadcast it are sold worldwide and, as with Blue Planet 2, he or she who pays the piper calls the tune.
From 1975, metric measures have been used in the game. For example, the 25 yard line became the 22 metre line.
Fuel efficiency figures
Official fuel efficiency figures for vehicles are expressed as litres per 100 kilometres (L/100 km). The lower the figure, the more fuel-efficient the vehicle. Typical values fall between 4 and 10 L/100 km.
Emission levels are expressed as grams per kilometre (g/km) in car advertisements and reviews.
Driver location signs and marker posts
Driver location signs and marker posts show the number of kilometres from the start of the motorway. These reference markers are used by the emergency services to locate incidents.
Kilometres are shown on some footpath signs around the UK, either alone or alongside miles. Contrary to the impression created by groups that specialise in vandalising signs, those which have planning permission meet legal requirements whatever units are used.
Some newspapers and magazines use kilometres to express long distances in their reports, either alone or alongside miles. However, some national British newspapers appear to prefer miles to kilometres. Usage varies between newspapers. Some have a policy of letting their journalists use what units they like. Television and radio programmes aimed at an international audience that are broadcast in the UK, such as BBC Newsday, tend to use kilometres.
Canal and river navigation signs
Canal and river signs are not covered by the derogation for the continued use of miles, yards, feet and inches on British road signs. So canal and river signs must show kilometres for distances and kilometres per hour for speed limits.
Modern tram and light rail systems
Modern British tram and railway systems such as the Docklands Light Railway (DLR) and the Croydon tram network are entirely metric and use kilometres. As the metric ERTMS signalling system is rolled out over the next 20 years, the use of kilometres will increase on British railways (see https://metricviews.org.uk/2014/08/metrication-of-the-rail-network/ for more details).
Diamond-shaped speed signs for tram drivers use a white background with a black border. The black digits that appear on these signs represent tram speed limits in kilometres per hour. These signs are only intended for tram drivers.
Ordnance Survey maps
Ordnance Survey maps use a kilometre-based grid and have used metric scales for over forty years.
Commercial road atlases
Commercial road atlases use kilometre-based gridlines and dual scales. Typically, the scales use both miles and kilometres. Despite the fact that the Ordnance Survey is exclusively metric and is the basis for commercial map makers, dual-measurement road atlases are undoubtedly strongly influenced by the continued use of miles on British roads.
Funfair ride information
Information about funfair rides was given in metric units, including speeds in kilometres per hour. I wrote about this in a previous Metric Views article, which you can find at https://metricviews.org.uk/2015/11/model-metric-citizens/.
High Speed 1
Britain’s only high speed line, HS1, from London St Pancras to Folkestone, has speed limit signs in km/h (shown as “KMH”).
Tachographs and speed limiters for large vehicles
Tachographs use kilometres to record the travel distances for big vehicles. The speed limiters used for big vehicles are based on kilometres per hour, which is incompatible with official speed limit signs on British roads.
Motorcycle tests include an emergency stop at 50 km/h, which is the standard speed limit for urban areas throughout Europe, except the UK of course. You can find out more about British motorcycle tests in a previous MV article at https://metricviews.org.uk/2010/04/dft-imperialists-waste-more-taxpayers%e2%80%99-money/.
Documentaries and science programmes
Documentaries and science programmes often use kilometres.
The information displayed on exercise equipment at gyms is typically metric. That includes the number of kilometres run on treadmills. Motion speeds (e.g. running, rowing, cycling, etc.) tend to be shown in kilometres per hour.
British legislation and official publications
Official use of measurement units is metric for most purposes with only limited official use of imperial (i.e. road signs, draught beer and cider, doorstep milk and precious metals). This includes the use of measurement units in British legislation. For example, the Commons Act 2006 uses square kilometres for land areas (source: http://www.commonsreregistration.org.uk/). Road traffic volumes are published in both kilometres and miles (source: https://www.gov.uk/government/collections/road-traffic-statistics). Government publications also tend to use kilometres.
Speedometers in cars sold in the UK show both miles and kilometres. This is a legal requirement.
Visibility levels are expressed in metres for short distances and kilometres for long distances. The UK Met Office has been metric for most purposes for over 50 years.
Readers may be able to suggest additions to this list.