The National Street Gazetteer (NSG) is the definitive reference system used in the notification process and the coordination of street works. Under legislation, each local highway authority in England and Wales is required to create and maintain its own Local Street Gazetteer (LSG) and Associated Street Data (ASD). These are then compiled into the only master index built to the national standard BS 7666, for access by a number of other organisations via the NSG online hub and managed by Intelligent Addressing.

Required under the New Roads and Street Works Act (1991), the NSG contains more than 1 million streets. It is an unambiguous referencing system, using Unique Street Reference Numbers (USRNs) to identify any length of highway or road in England and Wales. Set up initially to improve highway maintenance, the NSG enables local authorities to coordinate activities and the utilities to know where and when to dig holes.

On a monthly basis, all 172 highway authorities across England and Wales upload their LSGs, along with ASD, to the NSG hub. This enables third party organisations such as public utilities to meet their highway statutory requirements to provide the appropriate street works notifications. Local authorities are required to provide monthly updates.

The legislation requires that all publicly maintained highways, prospective publicly maintained roads, as well as private roads are recorded in the National Street Gazetteer.

The following types of streets are included in the NSG:

• motorways
• classified principal streets including trunk roads and other classified numbered streets
• other publicly maintained unclassified numbered streets
• prospective publicly maintained streets
• private streets known to the highway or roads authority
• cycleways
• remote footpaths
• subways that are publicly maintained
• maintained or mettalled footpaths.