Kirkstall Gyratory System
This page describes the ongoing problems with the Kirkstall gyratory system and the neighbouring highway network. This system dates from a series of bizarre planning decisions in 1994. So far it has been re-designed on six occasions. It has never worked in a wholly satisfactory manner, and now threatens to fail spectacularly when it is first tested under full load.
The map shows the gyratory as it will be when the new Metric development opens on Bridge Road.
The basic problem with the design is that many of the road links between the traffic signals are too short. This means that they cannot store sufficient vehicles when their exit signal is at red, and when this signal turns green these reservoirs are soon exhausted. Green signal time is "wasted" waiting for vehicles to arrive from more distant junctions. The problem can be minimised by synchronising adjacent signals, or by shorter signal times, but this increases the overhead for stopping and starting. Any pedestrian phase must be long enough for people to safely cross the road.
Traffic signal timing is optimised by computer, often with a final human "tweak". For one-way systems it is easy to create synchronised "green waves" which shepherd platoons of vehicles through the network, every signal turning green just as the leading vehicles arrive. But for this network the scope for optimisation is severely limited, because all the roads are two-way and the gyratory has two counter-rotating flows moving in opposite directions. Every right turn conflicts with vehicles coming the other way. Several previous designs had poor accident records as a result.
The shortest links are on the A65 between Kirkstall Lane and Savins Mill Way, the left flare from the A65 northbound into Savins Mill Way and Wyther Lane outside Hollybush Farm. These short links seriously degrade network performance. There are new short links on Bridge Road associated with the Metric development. We do not know how these will perform in practice. There is serious conflict between buses and customers queueing for Morrisons on Savins Mill Way.
It is difficult to get traffic into and out of the former Tesco site between Kirkstall Lane and Beecroft Street. This site slopes steeply uphill from west to east. The junction between Beecroft Street and Kirkstall Hill is 30m higher the junction between the A65 and the B6157, or a gradient of 1 in 10. The difference in height is equivalent to a ten storey residential building. Tesco claimed that Beecroft Street was too steep to accommodate modern delivery vehicles, but produced no evidence to support their assertion. Tesco's proposed "solution" in their now-abandoned planning application would have caused serious inconvenience to local residents, and impeded the free movement of emergency vehicles.
The gyratory has been known to saturate occasionally at peak times, but it has never been properly tested under full load. When Morrisons first opened they fairly quickly drove the old Kwik Save supermarket out of business, so two high-volume food stores have never traded in Kirkstall at the same time. Allders was always a low-volume outlet, and BHS did little better, but the new retailers in the Metric Development on Bridge Road are likely to trade intensively, with high rents and a huge capital investment to pay off. Meanwhile work has started at Kirkstall Forge, which has scarcely figured in previous road traffic calculations.
The development plan for Kirkstall Forge has changed over the years, and over-optimistic assumptions are often made about the number of rail passengers. Highway officers have realistically modelled the traffic flows for the new junctions on New Road Side and Vesper Gate, but we have seen no evidence that these figures have been correctly propagated across the rest of the highway network.
The Forge developer has made no contribution to gyratory improvements, and Metric only made a small payment. None of the local developers and retail operators is presently meeting the full economic cost of their business activities. There is a danger that all the accumulating backlog of highway improvements from the last twenty years might be charged to the last developer to start work, which is likely to be the new owner of the former Tesco site. This could preclude any social housing on this site, and might render it permanently unusable. It could easily remain a derelict eyesore for the next twenty years.
It is possible to prevent the gyratory seizing up by rationing the number of vehicles entering the system, but this creates long tailbacks on all the approach roads. These queues eventually extend back to the point where they block remote junctions. This already happens on major orbital and radial routes at peak times, and in future we can expect this for longer and longer periods each day. Kirkstall Bridge is the only river crossing for a mile or more in each direction, so the inability of this system to cope with orbital demand has adverse implications on both sides of the valley.
It does't take a genius to see trouble coming, and highway engineers now acknowledge that the gyratory will fail at some point during the current planning period. The only questions are when, and what shall we do when the inevitable happens?
Last updated 5 July 2015 at 10:02. Back to the top
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