218B. M1 Motorway, Abbots Langley, Three Rivers, Hertfordshire Located at Junction 6 of the motorway (the Waterdale Interchange), with access to the A405 below, are a number of tapered sheet steel support columns and associated tensile cabling left over from an earlier, and unusual, 1980s' catenary-based lighting system that used to commence at Junction 8 (Breakspears Interchange) and continue to a point just south of Junction 6, near the Bucknalls Lane over bridge. The lanterns employed were CU Phosco P415s, and ran two 180 Watt SOX (low pressure sodium) lamps, with the lamp control gear being installed within them too. As can be expected, this made the lanterns very large and bulky. Surprisingly, the lamps were arranged in a way that positioned them parallel to both carriageways, rather than perpendicular over each carriageway, as is the case with regular street lighting units. Much of this catenary scheme was removed after April 2021 (although, it may have been deactivated for some time before then), but a short section still remains here owing to the apparent difficulty in removing the equipment safely. By the time of removal, this was the last catenary-based lighting system to exist in the UK.
Three P415s survive on the section that passes over the A405 (two are pictured below; the third is further to the left, behind the column supporting the dayburning Philips SGS 203). I assume that because these lanterns are positioned above a live carriageway, taking them down was too risky without closing that road too.
The lanterns are GRP in construction (probably, a necessity, owing to their considerable size), with each one being supported at either end. The upper wire between each mast then provides the support for the lantern, while the lower wire supports the supply cabling.
Depending on where the lantern is installed on the catenary wire, the length of the support brackets differs, with central lanterns having the shortest brackets.
Where the lanterns have been removed, the support wires remain, but the cables are cut at each former position.
An array of horizontal cabling is seen here, as the nearby high voltage electricity transmission lines come into view behind the catenary cables.
The gap between the M1 bridges allows the three lanterns straddling the A405 to be seen clearly.
Looking up at one of the examples above the A405, the two lamps remain visible within the lantern. The two white boxes at either end of the fitting house the control gear for the two lamps.
The bayonet cap for one lamp is located at one end of the gear compartment, while an extension to the internal support frame provides end support for the second lamp.
The two surviving lanterns over Chequers Lane are seen here.
This view demonstrates the tray-like shape of the lanterns.
This 10 m tubular steel column supporting a Philips MA 50 135 Watt SOX lantern (with the lamp control gear housed in the column base) is positioned alongside the pedestrian footbridge over Mount Pleasant Lane. I suspect that the MA 50 has survived here because of the bridge's proximity, which could lead to access issues for maintenance vehicles.
The close-up reveals that the MA 50's bowl looks to be rather full of dirt and water, suggesting that it hasn't worked for some time. As the street lighting in this area (but excluding the M1 lighting) is group-controlled from a master photocell on a column adjacent the bridge, a Royce Thompson B16 NEMA shorting plug is employed here, rather than a standalone photocell.
A little further north of this section, where the M1 and the M25 connect, several short columns supporting floodlights also running SOX lamps remain in place, but are probably also no longer in use. Owing to there being no safe means of photographing these luminaires, Google Street View screenshots are used instead.
The floodlights look to accommodate 90 Watt lamps, with a Zodion SS4 photocell being fitted to this example to switch it off and on. With the floodlights being located beneath a bridge, the switching accuracy of these photocells is likely to have been compromised.
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