So, what are these gantries and how did they come about?
In 1964, the new TSRGD brought in following the Worboys report had no real detail for motorway gantries. As discussed in another article, this meant that situations on some motorways could not be signed within the existing regulations. As a consequence, there were many experimental designs, but the most striking examples of this have to be from Glasgow.
In the early 1960s, comprehensive plans were being drawn up for a series of motorways surrounding Scotland’s largest city. This was revolutionary thinking at the time, inspired by what had been accomplished in California. One aspect that needed serious consideration was the way drivers would be directed around this complex system.
It came to pass that in 1970, when the first gantries were erected on the Kingston Bridge (now a major part of the M8 through the city) the design had been agreed upon.
Typical first generation Glasgow Gantry. Photo courtesy of Stuart Baird.
At first glance, they’re not much different from modern gantries, but there are several significant difference that you need to know about to successfully understand the sign.
- The use of overhead signals for lane control and traffic management was still in its infancy. There was, therefore, no guidance whatsoever on how best to use this technology. In Glasgow, it was decided that the signals would be used in lieu of the more familiar downward pointing arrow from TSRGD 1964.
- As there were no prescribed gantry signs for situations not involving a lane drop, Glasgow’s engineers yet again had to improvise. Their decision was to use two signals; one to refer to the departing route, and one to refer to the main route. As a result, if you see two signals squashed close together that means the left hand lane carries on beyond the junction.
- At the actual exit itself, the departing route sign would use the colour of whichever class of road it exited onto.
The vertical height of the sign faces varies from 1200mm, to 2500mm. These discrepancies have usually been due to different design engineers working on different contracts.
These signs were all to be internally illuminated with maintenance access protected from the elements, so the overall surface area needed to be kept as small as practical. In a number of cases this has resulted in mixed x-heights, which is rather messy. It can be somewhat justified in the fact that the approach speeds of vehicles using the motorway system is often well below 70 mph (indeed, with a few exceptional lengths of the M8, none of the truly urban Glasgow network has a speed limit higher than 50 mph).
The first generation signs were constructed from ink dyed acrylic, which whilst not only heavy – as unfortunately realised when one shattered and fell out of its frame in 1981, suffered from severe degradation caused by moisture ingress. These started to be replaced with vinyl faces and were all removed by 1994.
A failed sign face. Photo courtesy of Stuart Baird.
So, now that we have conventional gantries, why hasn’t Glasgow adopted them? The simple reason is economics. The original gantry designs were of their time, and they have all been designed to co-operate with other gantries within the same system. Whilst it would theoretically be simple to just revert to normal signs, this requires replacing over 130 gantry units across Glasgow. This is a vast expense purely to provide a modern sign design.
There is also the fact that despite being utterly non-conventional, the Glasgow signs are efficient in their use of space. For instance, this is what the approach to junction 29 – where no lane drop occurs eastbound – would look like if it used a conventional gantry sign.
Note how the sign is now extremely tall. This uses consistent x-heights, but the size of the sign makes it impossible to retrofit to an existing gantry structure. As we know, gantries are not cheap and internally illuminating a sign of that size would also be impossible to do with an acceptable result.
Glasgow’s non-conventional approach results in a much smaller sign height wise.
Whilst the Glasgow system does have several flaws, and it is nowhere near resembling a prescribed sign according to TSRGD, there are some advantages in the city retaining this unique system. It is telling that, given historically the Ministry of Transport were very quick to condemn signage systems they did not agree with (see what happened in Oxfordshire in the early 1960s, for example), there is no record of Glasgow being told to sort itself out. That may well just be because none of the system was originally part of the trunk road network and was designed by the former Strathclyde authority; but it also is telling that Transport Scotland have no plans to abandon the system either as the recently finished M74 and M80 motorways both have the same system applied to them.
Jonathan Winkler, who I consider quite an expert on such matters, got in touch to present the following alternative viewpoint about why these signs have survived:
Scotland acquired responsibility for its own trunk roads in the mid-fifties (1956, I think), and this presumably also included the right to issue ministerial approval for non-prescribed signs within Scotland. While there has always been interdepartmental coordination since that date, there are certain aspects of Scottish non-prescribed signs that differ significantly from England and in fact draw criticism from English traffic signing professionals when pointed out to them on SABRE:
* Issue of blanket authorizations covering all of Scotland (the English position is that a nonprescribed sign has to be separately approved for each local authority)
* Use of the Diagram 616 no-entry sign with supplemental plates that specify exceptions (e.g. “Except buses,” “Except cycles”)–called out specifically as a no-no in the regulatory signs chapter in the Traffic Signs Manual
Interestingly, the M8 completion is being done conventionally, but that is due to the fact none of it is within the city of Glasgow proper.