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Traffic Control in Sheffield
Context:
Sheffield shares the challenges facing South Yorkshire - to manage the transition from an economy based on employment in coal, steel and ancillary industries, with localised journey to work patterns encouraging high levels of walking, cycling and bus travel and rail freight, to an economy dominated by new service and high-tech industries with more dispersed patterns of journey to work, with potentially high levels of car dependency and reliance on road freight. Economic activity levels in Sheffield and South Yorkshire were relatively low in the 1990s and traffic congestion was also limited. However, the Objective 1 intervention is stimulating an increase in economic activity. This is reinforced by the fact that since 1991 South Yorkshire has experienced very rapid growth in car ownership, albeit from a very low base. The number of cars in Sheffield increased by 28% between 1991 and 2001. This increase is reflected in the relatively high rate of traffic growth, which has been in excess of 20% over a similar period.
Network:
Sheffield is the third largest city in England, it covers an area of 36,333 hectares, has a population of 513,234 and 2,097 miles of roads. The road network is constrained by the physical geography of the area and by historical transport priorities. Most major routes follow the narrow and steep river valleys, with comparatively few, low capacity, links between them. Although the basic layout of the strategic network is based on a ring and radial pattern neither the inner nor outer ring roads is complete.
Sheffield has no urban motorways and there are grade-separated intersections only on the A57 Sheffield Parkway. The inner ring road intersections are all at-grade and most are over-capacity at peak periods. During the road building boom of the 1970s South Yorkshire concentrated on public transport subsidy, consequently a major part of the strategic network is based on single carriageway multipurpose roads, many of which pass through district centres. Most junction layouts are constrained by surrounding buildings. There are limited opportunities to improve capacity.
Traffic Control Infrastructure:
Most junctions on the strategic network deal with unbalanced flows at peak periods, which cannot be adequately controlled by roundabouts. All significant junctions, including those laid out as roundabouts, are controlled by traffic signals, at least during peak periods. The city's Urban Traffic Control (UTC) system controls all major junctions. There are more than 430 signal installations (including pedestrian crossings), 75% of them are connected to the UTC system, including 95% of those on the strategic network, a further 10% are monitored by the remote monitoring system. All new junctions are connected to the UTC or remote monitoring systems on installation. The city also operates and manages maintenance of the motorway traffic signals on the M1 and M18 in the South Yorkshire area as agent for the Highways Agency.
The city has over 150 signalled pedestrian crossings, including pelican, puffin and toucan (pedestrian and cycle) crossings. 40% of the crossings are connected to the UTC system, this includes most of those on the strategic network, 25% of the remainder are monitored by the remote monitoring system.
Closed Circuit Television (CCTV) cameras are installed in more than 30 locations for traffic monitoring, and the system can exchange images with the city centre security CCTV system. Cameras cover the whole length of the existing Inner Ring Road, the Don Valley Link Road, the Meadowhall Centre area, the Outer Ring Road at Manor Top and Gleadless, the Parkway at Handsworth and Penistone Road at Hillsborough. The city also controls CCTV cameras on the M1 at junctions 31 and 34. There are more than 200 traffic counters connected to the UTC system producing data for network monitoring.
A variable message signing system is installed to provide car park occupancy information for the 10,000 spaces at the Meadowhall Centre. Variable message signs are also used to control part time bus-only restrictions on Boston Street and the Heeley tidal flow system. A new UTMC-compatible system has been recently introduced to provide provide parking and other travel information throughout the city, initially it is providing car park occupancy information in the Charter Row area.
The Supertram system runs mainly on-street sharing the carriageway with rubber-tyred vehicles. It is controlled by 71 traffic signalled junctions and pedestrian crossings. At all of these the tram can take absolute priority over other traffic, but at a small number the UTC system is used to manage the priority to prevent network effects from obstructing other trams or major traffic flows.
Traffic Control Principles:
The basic policy direction for traffic control was established in 1987, shortly after highway authority responsibility was transferred from the former South Yorkshire County Council. The objectives were to avoid gridlock, minimise congestion and adjust the balance of priority away from the private car towards buses, pedestrians and cyclists. These objectives have been reinforced by UDP transport policies and the council's declared transport priorities which aim to provide travellers with a choice of modes of travel.
The network is designed to operate with short traffic signal cycle times, to maximise capacity of flared approaches and provide frequent pedestrian crossing opportunities. Queuing on the approaches to oversaturated junctions is controlled so that congestion is minimised and queues are relocated to places where bus lanes allow public transport to bypass the queuing traffic.
Because of these principles, and because many of the major junctions in Sheffield are signalled roundabouts, or have closely associated stage streams, control by SCOOT UTC has not been appropriate for much of the network. However, because the latest versions of SCOOT provide more control techniques, we are now beginning to investigate its use on parts of the network.
Pedestrian crossings in the city are designed to give pedestrians as good a service as possible without leading to major congestion for vehicular traffic. Timings are varied during the day so that more pedestrian priority is given outside peak traffic periods. In general pedestrians have to wait for less than 20 seconds for a crossing to respond, in many cases the crossing will begin to change as soon as the pedestrian presses the push-button. The UTC system is used to prevent this flexibility leading to unacceptable congestion, but the degree of priority given to pedestrians at crossings in Sheffield remains greater than that given in many other cities in the country.
Challenges and Opportunities:
UTC, as part of the Council's Development Services, faces many challenges to its ability to provide a satisfactory service. However, there are also a number of opportunities which will allow us to improve the service we offer.
The challenges we face within a fixed budget and with limited resources include:
- The need to manage the network in accordance with the requirements of the 2004 Traffic Management Act;
- Increasing numbers of sites to maintain;
- Expectations by travellers for up to date information about traffic conditions;
- Requirements for the city to reduce the environmental effects of traffic;
- The need to replace the existing UTC communications system which is based on obsolete technology.
The opportunities to address some of these problems are:
- Developments in Intelligent Transport Systems (ITS) technology will provide new tools to attack traffic problems without requiring expensive infrastructure improvements;
- Identifying "invest to save" opportunities, to refurbish equipment and update communications so reducing ongoing maintenance and line rental costs;
- Identifying opportunities, such as the need to replace the UTC communications system, to develop partnerships with other bodies, to pursue jointly-funded developments.
For further information contact: traffic.control@sheffield.gov.uk
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