In the United Kingdom, trunk roads were first defined for Great Britain in the
Trunk Roads Act 1936 (
1 Edw. 8. & 1 Geo. 6. c. 5). Thirty major roads were classed as trunk roads, and the
Minister of Transport took direct control of them and the bridges across them. The Trunk Roads Act came into force in England and Wales on 1 April 1937, and in Scotland on 16 May 1937. This development did not extend to
Northern Ireland, which has always had a separate system of highway and road traffic law. At that time, of British roads were classified as trunk roads. Additional roads have been "trunked", notably in the
Trunk Roads Act 1946 (
9 & 10 Geo. 6. c. 30). Others, like virtually all British motorways, have entered the system as a result of new construction. As of 2004, Great Britain had 7,845 mi (12,625 km) of trunk roads, of which 2,161 mi (3,478 km) were motorways. Since 1994, trunk roads in England have been managed by
National Highways (formerly Highways England, and before that, Highways Agency), while
Scotland has had responsibility for its own trunk roads
since 1998; these are currently managed by
Transport Scotland, created in 2006. The
Welsh Government has had responsibility for
trunk roads in Wales since
its establishment in 1998. England has , Scotland has and Wales has of trunk roads, inclusive of motorways. National Highways publishes a full network map of trunk roads and motorways in England. Most interurban trunk roads are
primary routes, the category of roads recommended for long distance and freight transport. Not all primary routes are trunk roads, the difference being that maintenance of trunk roads is paid for by national government bodies rather than the local councils in whose area they lie. Primary routes are identified by their direction signs, which feature white text on a green background with route numbers in yellow. Trunk roads, like other "A" roads, can be either
single- or dual-carriageway. Historically, trunk roads were listed on maps with a "T" in brackets after their number, to distinguish them from non-trunk parts of the same road, however this suffix is no longer included on current
Ordnance Survey maps, which simply distinguish between primary and non-primary "A" roads. A trunk road which has been upgraded to motorway standards may retain its original "A" number, but with an "M" in brackets to denote that motorway regulations apply on it. Long distance examples of this are the
A1(M) in England, and the
A74(M) in Scotland.
De-trunking It is possible for roads to be "de-trunked" – for example, when superseded by a motorway following a similar route – in which case they normally become ordinary
"A" roads. When a road is de-trunked, signposts are often replaced, and sometimes route numbers are changed, making the original route of the road harder to follow. Roads are formally and legally detrunked by
statutory instruments named 'Detrunking (or sometimes
De-Trunking) Orders' which include a plan of the route being detrunked. The routes to be detrunked (as set out in detrunking orders) are not always linear sections, but can be split into multiple sections, and span multiple counties. In England, the government has de-trunked much of the trunk road network since the late 1990s, transferring responsibility to local councils to allow National Highways to concentrate on a selection of core trunk routes, mostly dual carriageways and motorways. == Sweden ==