Maintenance Compound

Maintenance Compounds (often signposted as a works unit) are facilities provided by a national or local authority, or a contractor on their behalf, to maintain vehicles and resources required to run and repair the local road network. Generally, this is focused on winter maintenance and forthcoming roadworks.

Introduction of Trunk Road Depots

When Trunk Roads were introduced in 1937, very few bypasses had been built, so the vast majority of the network could be easily accessed from nearby towns. As a result, it was decided the local authorities would continue the daily maintenance of these roads.

When the M1 opened in 1959, it became clear this situation was now far from practical. As a result, depots were attached to the service areas built at Watford Gap and Newport Pagnell to allow winter maintenance to be prepared and works vehicles to be parked.

This prompted an urgent review, which concluded depots like these should be provided every 12 miles - a figure based on the typical reliable range of a works vehicle at the time. Coincidentally, 12 miles was exactly the same as the distance suggested between service areas. Keen to get these new depots through the planning process as quickly as possible, and worried about roads such as the A1(M) Doncaster Bypass which offered little space for any more exits, it was decided all motorway maintenance compounds would be attached to motorway service areas.

Even so, before building each one, the option of attaching it to a nearby junction instead was considered. The main benefit was that these could double-up as local council depots at the same time. At a few locations this was taken up: Shepshed Interchange was used instead of Long Whatton services, Breakspears Interchange was used instead of Redbourn services and Bury Court was used while debate was being held about whether the M50 would have a service area.

Meanwhile, at the Blyth Interchange on the A1, a trial motorway-style depot was built to serve the Blyth Bypass, which would be treated like it was a motorway. Although it was a trial, its need was considered so urgent it was rolled out almost immediately.

Creation of Standalone Motorway Compounds

By 1969, complaints that motorway compounds were significantly hindering the operation of the service areas caused a review of policy, and it was instead decided that a motorway maintenance depot should never be attached to a service station. By this point, the majority of the core motorway network had already been built, but many of the later additions had depots built at junctions at regular intervals.

Unusual Works Units

The legend "works unit only" is used to signpost motorway exits that need not be used by anybody else, but sometimes it is used for other facilities general traffic should not be using.

• The M4 has an exit for RAF Welford which is signposted with "works unit only" on red-bordered signs.
• The M27 Hamble Bridge westbound has a signposted "works unit only" which is actually a track used to inspect the bridge.