The United Kingdom has a well developed and extensive network of roads totalling about 262,300 miles (422,100Â km). Road distances are shown in miles or yards and UK speed limits are indicated in miles per hour (mph) or by the use of the national speed limit (NSL) symbol. Some vehicle categories have various lower maximum limits enforced by speed limiters. A unified numbering system is in place for Great Britain, whilst in Northern Ireland, there is no available explanation for the allocation of road numbers.
The earliest specifically engineered roads were built during the prehistoric British Iron Age. The road network was expanded during the Roman occupation. Some of these roads still remain to this day. New roads were added in the Middle Ages and from the 17th century onwards. Whilst control has been transferred between local and central bodies, current management and development of the road network is shared between local authorities, the devolved administrations of Scotland, Wales and Northern Ireland, and National Highways in England. Certain aspects of the legal framework remain under the control of the United Kingdom parliament.