Plessey 'Mellor' Traffic Signal

Acquired in September 2024.

This traffic signal head was an eBay purchase, after I decided that acquiring a 'Mellor' signal head would be a good idea. The Mellor name derives from designer David Mellor (1930 - 2009), who was tasked with redesigning the humble British traffic signal, following a Ministry of Transport report in 1963, which concluded that the existing traffic signal system (dating back to the 1930s) was in need of modernisation. The new design was unveiled in 1968, before being rolled out in the early 1970s, and must have seemed the height of modernity at the time, with its innovative all-plastic construction providing a more durable and weatherproof solution, along with its use of tungsten halogen capsule lamps positioned within parabolic aluminium reflectors, and modular construction, allowing the basic design to be adapted depending on the needs of the location. The same basic design continued in service, with little alteration, until the late 1990s / early 2000s, though even today, modern signal heads borrow greatly from the Mellor design.

This particular example comprises the standard 8·5 inch (216 mm) prismatic red and amber aspects, fashioned in acrylic, along with 12 inch (305 mm) green arrow and permanently operational Turn Left arrow aspects - the most basic version of the signal head having an 8·5 inch green aspect too, and no additional signage. One thing that I had not appreciated, prior to acquiring the signal head, was its size - This. Is. Flipping. Huge. It measures 46·5 inches (1·18 m) in height, and 35·5 inches (0·91 m) in width at the widest point. Add to that the fact that it is incredibly heavy, and I wonder how DHL managed to deliver it at all, especially with it arriving in several boxes that had been taped together for its trip across the Irish Sea - its original location having been in Northern Ireland! The main signal head body is surrounded by a tough flexible plastic frame, which originally, would have had a reflective white stripe applied to it - the faded remains of this remain visible - and two white plastic sections at the top and bottom to join the two parts of the frame together. A quirk with the traffic signals around London (and other places these days) is that these frames are omitted, resulting in a surprisingly different appearance. A very similar signal head to this one (but with the fixed arrow sign facing left instead of right) suffered considerable damage during a bomb blast in Manchester on the 15th June 1996; its remains are preserved on display at the city's Museum of Science and Industry, as seen here.

'Plessey Automation' is moulded into the rear of the signal head, dating it to no later than 1989; this being when GEC-Siemens took over the Plessey company. Although a few companies produced the Mellor heads, including Page Signals and GEC-Elliott, all were required to follow the standard Mellor design closely, meaning that there are few differences between products from different companies.

Access to the lamps is gained by removing a locking pin on the left-hand side of the red and amber aspects, or one on either the left or the right on the larger green aspect. Whilst the lamps in the red and amber aspects then become accessible, for the green, the lamp is attached to a long tube that is secured into the optic using a clip - once this is removed, the tube can be eased out, and the lamp replaced. Disassembly of the green aspect is possible, but very time-consuming; not least, because of the sealing compound that exists between the reflector and the glazing panel.

The red and amber reflectors are screwed into the signal head body - with one screw removed, and the other loosened, the reflector will hang out of the body, allowing access to the 12 volt transformers located behind. Notice the failed halogen capsule lamp that has been discarded in the bottom of the signal. The current amber lamp is, similarly, quite blackened, and probably doesn't have long left.

One of the three transformers is visible with the red aspect reflector removed - the transformers are stacked one-on-top-of-the-other on a frame.

When powered up, the regulatory Turn Right arrow sign illuminates immediately, though all is not quite as it seems with this.

Originally, two 6 Watt fluorescent lamps were positioned behind the diagram to provide a means of backlighting; however, the signal head's previous owner replaced that setup with a Tamlite 28 Watt 2D bulkhead fitting instead, which fits perfectly within the aperture. Part of the reason for this was that the white backing to the Turn Right sign had worn away, creating a transparent image. With the bulkhead having a translucent cover, the white background is restored.

Another alteration made is the addition of this electronic control module, located on the back of the signal. This allows various worldwide traffic signal sequences to be emulated, and the times for which each aspect is on, to be set. Setting 3 appears to be the UK version, although setting 38 (the highest available) seems to be to use on a UK wig-wag (i.e. level crossing and similar) signal, with the red and amber on the traffic signal head flashing alternately, and the green being the initial amber that shows just before the crossing sequence commences. The '001' shown on the display is the time that an aspect (in this case, the red one) is lit, in seconds - the knob to the right allows the time to be increased (or decreased).

Once the sequence is activated, the red aspect glows first, and probably earns Billy Ocean a few extra pennies in royalties in the process.

The 'prepare to go' indication of red and amber demonstrates the classic Mellor lens glow nicely.

The slightly more concentrated green arrow beam played havoc with the camera's brightness settings. An alternative option, when arrow aspects were employed, was for the arrow to be produced using fibre optics - I remember seeing these for the first time in the early 1990s and considering them "futuristic" at the time!

To complete the sequence, the single amber "prepare to stop" aspect is displayed.

This video demonstrates the signal's operation, including the characteristic fading in and out of the halogen lamps, which does not occur with modern LED signal heads. In something of an act of sacrilege, I replaced all of the lamps with LED equivalents - the video shows the difference too. Seeing the 'vintage' Mellor signal head with "instant" illumination to its optics looked very peculiar indeed!

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