Set by Barney Smith, Programme Director, Bristol City Council and Interim CEO, Bristol is Open
Like many Local Authorities, Bristol City Council is committed to tackling congestion and supporting Bristol's economic growth. To this end, the council run a traffic control service which aims to keep traffic moving around the city network by making the best use of the available road network and providing accurate, up to date traffic and travel information to the public.
In order to achieve this, the traffic control team utilise Urban Traffic Management and Control (UTMC) systems. A number of different technologies are used, including a car park guidance system and a variable message signage system, which allows traffic control staff to pass messages to drivers at the roadside. The most critical system in use is the UTC/SCOOT traffic signal control system. This system connects all sets of traffic signals in the city to a central computer, which uses live traffic flow data from on street detectors and automatically adjusts signal timings to provide more green on the busier approaches when required. It also calculates offsets between sets of signals to minimise wasted green time and maximise the capacity of the available road network. However, this does not mean that the system can increase capacity. The UTC system attempts to run the network as close to 100% capacity as possible, by minimising wasted green time and assisting vehicle progression through the network.
This can provide an improvement of 5 - 12% over local traffic signal control methods. Furthermore, during incidents, roadworks or events on the network, traffic control staff intervene, making changes to the working of the SCOOT model to minimise the impact of the incident.
All of these technologies and interventions have assisted the city to manage increasing traffic flow levels to date.
However, traffic flow levels in the city are continuing to increase and are now at extremely high levels. The difference between the capacity of the city network and the level of traffic demand is now so large that at busy times of year, the network has been caused to 'lock up'. This is due to the volume of traffic in the network, causing queuing traffic to 'interact' with other traffic movements and cause blockages. This causes a shockwave of queuing traffic that fans out across the network and affects the whole city.
Additional capacity cannot be generated by the UTC/ SCOOT system and nor can it be built. Therefore, as traffic flows have reached unprecedented levels and there is neither the budget nor available land to build additional road space, new thinking is required. Basically, a step change is needed in the way the city manages its road network.
The Solution? Bristol City Council invites the industry to develop an even better way of managing the road network.