Road speed limits in the United Kingdom are used to define the maximum legal speed (which may be variable) for vehicles using public roads in the UK. Speed limits are one of the measures available to attempt to control traffic speeds, reduce negative environmental effects of traffic, increase fuel use efficiency and satisfy local community wishes. The speed limit in each location is indicated on a nearby traffic sign or by the presence of street lighting. Signs show speed limits in miles per hour (mph) or the national speed limit (NSL) sign may be used.