MT 95/857

Motorway signalling: emergency light signals; M4 Motorway traffic supervisory system on elevated section

Date range	1964-1965
Location	National Archives (see all files stored here)
Catalogue	See entry
File base	Series MT, subseries MT 95

Context

Despite the promising file name, this file has virtually nothing to say on the emergency light signals on the M4 and is mostly concerned with the CCTV system installed on the elevated section shortly before it opened. Most of it is correspondence between the Ministry and Marconi, who seem to have sold the Ministry a very expensive and very experimental system in which the promised functions of selecting a camera, viewing its image and remotely panning and zooming it were prone to failure on a regular basis.

It also discusses the siting of cameras (almost exclusively on nearby buildings), diagrams the brackets supporting each one, discusses at great length how power would be supplied to central-reserve-mounted equipment (via the under-carriageway power duct, shockingly) and so on. It won't nail you to your seat but it might cure your insomnia.

Possibly the most interesting thing is that the various plan sheets showing the power supply ducts on the flyover also detail the location of lighting columns (some of which were lifted from the Chiswick Flyover's original western approach ramp and then installed on the new motorway deck, something unimaginable today), and also a plan of the under-carriageway heating system on the M4 elevated section, which is rarely mentioned and probably doesn't work any more.

Contents of note

• Diagrams of M4 elevated section with a few mildly diverting technical details.

People with camera copies

Chris Marshall has copies of everything of interest, which isn't much.