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Altrincham have conventional railway signalling, with line-of-sight running on the street-running sections in the city centre. A new TMS from Thales will replace the block signalling system. On the Bury and Altrincham lines, lineside

signals will be replaced with line-of-sight operation to achieve consistency across the network. There is a maximum permitted speed of 80km/h on the former railway lines outside the city centre, so magnetic track brakes are necessary for the required braking ability. The system is being provided with new trams from Bombardier and improved slip/slide controls should prevent skidding and wheel flats. An important feature of the new signalling

and control arrangements will be the ability to know where trams are at any given time. Radio beacons along the track will continually ‘talk’ to the trams and each other, allowing the control centre to monitor the position of each tram. This information will be used to trigger junction setting. This new signalling system should permit

closer headways, resulting in a more frequent service, as well as providing real-time service information. The new TMS from Thales has been trialled on Metrolink’s MediaCityUK branch in

Salford and is due to be rolled out across the entire network, but there has been teething problems which have led to delays.

Buses too The big bugbear in bus operation is traffic congestion. Bus lanes can help, but unless they are physically segregated they are subject to abuse by delivery drivers and others who need to get to the pavement. Urban Traffic Control (UTC) is a useful aid

in keeping buses moving. UTC is used to describe the technique of co-ordinating traffic signals, normally through a centrally located computer. Areas where signals are close together and traffic flows are high lend them - selves to co-ordination, as benefits are achieved by progressing platoons of traffic in an organised fashion. Simple UTC was available in the 1960s but

more sophisticated systems are used today. In London for example, over 500 signals are co- ordinated and controlled by a central computer. The reduction in delay to traffic generates benefits amounting to around £80 million per annum. The traffic management method used in London is known as SCOOT (Split Cycle Offset

Optimisation Technique). It was first introduced in 1984 in Westminster. SCOOT is now co-owned by Peek Traffic Ltd,

TRL Ltd and Siemens Traffic Controls Ltd. It is an adaptive system that responds automatically to fluctuations in traffic flow through the use of on- street detectors embedded in the road. Studies suggest that SCOOT typically reduces traffic delay by an average of 20% in urban areas. For buses, UTC methods such as SCOOT

are important as a light can be held on green for longer in order to allow a bus through a junction without stopping. Studies in London have shown that a reduction in delay of around three to five seconds per bus, per junction is typical. For buses to get a boost through the

UTC, the system must be informed of a bus’s presence either by selective vehicle detectors, i.e. using bus loops and transponders on buses, or by an automatic vehicle location (AVL) system. Bus management and informa- tion systems such as IBUS which make use of GPS technology to track buses through the network can be used to provide bus priority in SCOOT. The information gathered by such a system can also be used to drive ‘next bus’ indicators at bus stops.

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