PLANS being prepared by Network Rail will see the eventual end of the Imperial mile, chain and yard on the National Rail network, as a metric switchover takes effect during the next couple of decades.
The move will be triggered by the progressive installation of the European Rail Traffic Management System on selected routes between now and the 2030s.
The decision has been taken by the industry’s Technical Standards Leadership Group, Railnews has been told.
Although it will be necessary to permit the spread of metric-only ERTMS, the change will bring speeds and also locations, as presently indicated by mileposts, into line with the measurements already used on the rest of the railway.
Metres, kilos and litres have been standard for some time in such areas as civil engineering and rolling stock construction and maintenance, while the current Rule Book uses metric measurements as the primary units for distances, although speeds are still shown in mph.
The Rail Accident Investigation Branch also uses metric units by default, and translates the remaining Imperial terms where necessary.
The Rail Safety and Standards Board will now be assessing the implications of a further revision of the Rule Book and other documents to complete the changeover. At this early stage there are no firm costs or detailed timetable.
The traditional mileposts are expected to be replaced over time by new location markers at intervals of 500m or 1km. However, lineside speed restriction signs will become unnecessary in ERTMS areas, where information is given to the driver by screens in the cab instead.
Network Rail does have a derogation under the interoperability rules to show mph on cab screens as well, but a spokesman told Railnews that this option is ‘unlikely to be exercised’.
Some fully metric railways are already operated in parts of Britain. Apart from HS1, some London Underground lines and the ERTMS test area west of Shrewsbury, the country’s two segregated light railways in London and Newcastle have always been metric, while the speeds of modern trams are also measured in km/h.