While the headlines were still full of fog worries, and the Ministry of Transport was mainly preoccupied with emergency warning signs on motorways, local authorities were tasked with keeping the traffic moving on urban roads. By 1966 some of them were starting to ask themselves whether changeable signs might offer new ways to manage traffic flows.
Changeable signs for urban traffic control were not exactly new, of course: the alternate days "no waiting" signs were an early example, but automated signs had also been tried. In April 1964, a tidal flow scheme was introduced on Albert Bridge Road in West London, where automatic signs could change the road to operate either one-way or two-way depending on the time of day and the volume of traffic. There, large signs at junctions along the road, and small signs at various points along the way, took the form of boxes with a window at the front, inside which the various signs were installed on a roller blind. Motors would then scroll the blinds up or down to show the right sign. The scheme lasted, with more or less the same technology, until about 1990.
The Albert Bridge tidal flow scheme, with rollerblind "one way" signs visible on each side
Rollerblinds were a fairly primitive technology, and many of the schemes invented in the late 1960s and 1970s — even by local authorities — were much more adventurous.
Designs were first drawn up in 1968 for a system of direction signs in which letters and words would be picked out by points of light, which would look like a modern matrix display used on motorways today — but in this system, fibre optics would link the dots making up each individual word to a single lamp. This meant that the signs had a fixed number of words and alternatives hard-wired into them, and switching on or off a particular word or message could be done by switching a single light source on or off.
Even though this made the signs considerably simpler to operate than a modern matrix sign — in which each pixel is switched individually so that the options for displaying messages are virtually limitless — the signs still required computer control, and specialised equipment was ordered in 1971 to operate them.
There were two reasons to go for an unusual system like this: the first was that, approaching the complex junctions at either end of the expressway, drivers had to get in different lanes for different destinations, but with the number of lanes varying between two and four, the choice of lane would depend on the time of day. Changeable direction signs could show different destinations above different lanes as required. The other reason was to divert traffic away from the expressway if there was an accident or blockage: with no hard shoulder and no central reservation, Birmingham's highway planners feared that accidents would be harder to deal with and perhaps more severe than on other motorways. If something happened, they wanted a system that could advise drivers to go another way.
Testing of the new system started to take place before the road opened in 1972, and there is at least one photograph in existence showing the dot matrix destinations being tested on the approach to Spaghetti Junction. Ministry of Transport engineers reported that drivers seemed to have no difficulty in recognising the new displays as direction signs, even though they were not white-on-blue like normal signs, but while the idea was clever the actual implementation was a little bit disappointing. The text was not terribly easy to read and, once again, the aspirations of highway engineers seemed to be a couple of steps ahead of the technology.
It's not clear whether the Aston Expressway actually opened with its fancy signs in operation, but it's clear that they didn't last long, and they were replaced with normal, static motorway signs. The tidal flow system certainly remained switched off until 1987. The need to change the destination over each lane turned out not to be so important after all.
In Manchester, a different sort of tidal flow scheme was in operation, designed to make efficient use of a newly widened road into the city that had five lanes. The A34 Upper Brook Street was fitted with familiar overhead arrows and crosses to open and close lanes, and they were mounted on "lightweight gantries" slung across the road between the streetlights.
In August 1972 a prototype "secret sign" was demonstrated by Forest City, a major manufacturer of road signs and equipment based in Manchester, who were assisting Manchester City Council in providing better signs to explain the tidal flow system to drivers. They were using something that had been dismissed a few years before as unreliable: mechanically operated louvres.
The original designs had a series of horizontal louvres with the sign face screen-printed onto them and which were normally edge-on to passing traffic, like window blinds that had been opened to let the light in. When operated, motors rotated them to display the sign face, and when they were fully rotated, they would connect a circuit that brought fluorescent tubes on, so the sign was backlit.
- Photograph of the A38(M) Aston Expressway by Steven Jukes and used with permission.
- Photograph of Brook Street tidal flow system adapted from an original by Ben Brooksbank and used under this Creative Commons licence.
- Photograph of rotating prism sign near Brixham adapted from an original by Tom Jolliffe and used under this Creative Commons licence.