Priority for Public Transportation
Intelligent Transportation Systems
Intelligent transportation systems are information technologies that, when implemented in vehicles, on roadways, or centrally, can lead to vast savings in journey time, improved driver safety and convenience, and significant reductions in energy consumption and pollution (White 2002). Among the capabilities of current and future ITS technologies are the following:
- Traffic can be managed on the main roadways of major metropolitan areas through (1) control of road junctions and access to major routes, (2) rapid detection of and responses to incidents, and (3) communication of advice to drivers and passengers about traffic conditions (White 2002).
- A wide variety of information systems can be available to travelers. Drivers and passengers receive certain information by means of either eye-level ‘heads up’ displays or voice synthesizers installed within the vehicle (White 2002).
- Drivers can be automatically alerted to the proximity of other vehicles or obstacles. Under some advanced ITS technologies, automatic steering and intervehicle spacing control both facilitate collision avoidance and dramatically increase highway throughput (White 2002).
- Commercial vehicle operators can receive regulatory documents for multiple states in a single transaction. They can also undergo automatic weight checking without having to stop (White 2002).
- Continuous monitoring of the physical state of the road itself–as well as of bridges, tunnels, and the like–with early warnings of deterioration or structural weaknesses can be carried out through a network of probes embedded in the physical infrastructure (White 2002).
Priority Schemes and Systems for Buses
Priority systems are typically provided for buses, light rail and to a lesser degree heavy rail. Traditional priority schemes for public transportation has been provided through physical measures such as bus lanes, intended to allow priority vehicles by-pass traffic congestion. Because of technological developments, priority systems have become more effective and efficient in assisting public transport vehicles by influencing the operation of signalised junctions, and allow local authorities to manage the road network as a whole (www.dft.gov.uk).
A case for bus priority is made first of the grounds that buses should not suffer adverse effects from management schemes. As a wider policy, buses can be made more attractive, for example by permitting them to use direct route via contra-flow lane when other traffic is re-routed around a one-way system. They can thus retain more passengers. In conditions of scarce road space, giving priority to the most efficient users of that space (buses) may reduce total travel time within the network.
For the majority of road users, average time taken to pass an intersection is the only relevant criterion. The traffic engineer is also concerned with maximizing the flow of PCUs (passenger car units), in which a bus carrying 50 passengers traditionally receives little more weight than a single car. However, buses form a time-linked system, co that delays to one affect others (White 2002). Let us now discuss the different schemes and systems that are being used in the United Kingdom, particularly in London, to prioritise buses.
Bus Lanes/ Contra-Flow Schemes
By making a lane ‘bus only’, buses can overtake queues of other traffic. Many of these ‘with flow’ priority lanes were introduced during the 1970s, and they remain the most common form of bus priority measure. In order to avoid extra running time and diversion from passenger objectives when one-way schemes are introduced, buses may be allowed to continue to use a road in both directions, those against the (new) one-way flow in a ‘contra-flow’ lane. Although a few may be separated from other traffic merely by a solid white line (as for with-flow lanes) most are physically separated by a series of traffic islands or raised curbs. Major examples may be found in London, such as Tottenham High Road or Piccadilly. In some cases the concept may be taken further by having a segregated section of road surface for two-way bus traffic, as near Gare du Nord in Paris. A merit of contra-flow schemes is that they are largely self-enforcing, and substantial increases in bus speeds may be obtained.
Busways and Bus Links
The concept of providing bus priorities on existing roads may be extended to that of allocating the whole road space to buses, and/or building separate busways, usually conventional road structures of about 7.0 metres width, with one lane in each direction. They may provide new direct links, access to areas not open to general traffic, or routes parallel to existing congested roads. The simplest form is where an entire street is restricted to bus and delivery vehicle use only, typically a town centre shopping street from which other traffic has been taken by an inner relief road. Buses thus continue to serve the heart of the town, and cross-linking of services is made easy. Major examples include Queen Street in Oxford, and High Street in Exeter. The traditional road surface may be retained, with separate pavements, or the whole area resurfaced to permit mixed bus/pedestrian movement, as in Oxford. Average speeds may not rise substantially, but delays owing to congestion are largely avoided and excellent access provided. Within residential areas, bus links may be provided, in which direct routeing is provided for buses, but other traffic is banned. Buses thus benefit from efficient network structures, but intrusion from other through-traffic is prevented (White 2002).
Selective Vehicle Detection
Selective vehicle detection (SVP) is a bus priority method that enables buses to be progressed through traffic signals by prioritizing their passage to improve speed and reliability for passengers (www.tfl.gov.uk). Buses can be given the benefits of selective detection approaching traffic lights, enabling either an extension of an existing green phase, or bringing forward the start of the next green phase. Losses to the other traffic may be compensated by extending green time on the next phase (White 2002). Presently, the SVD system is being used to detect roadside beacon thus providing bus priority. When a bus passes a beacon, the transceiver fixed on the bus sends a signal to the traffic signal controller. The traffic signal controller then manages the sequence of the lights to assist the transit of the bus through the junction (www.tfl.gov.uk).
Automatic Vehicle Location
Transport for London (TfL) has recently obtained a modern Automatic Vehicle Location system known as iBUS. The system is intended for fleet management, passenger information and bus priority. The new system is based on GPS and supporting technologies for bus location. In this system, bus detector locations are configured in the on-bus computer and hence are also known as ‘virtual detectors’. The predefined virtual detector coordinates are compared with the location of the bus obtained from the on-bus navigation system to trigger a priority request. The request is made through radio messages from each bus to the traffic signals encountered en-route. This system eliminates the need of on-street hardware for detecting buses and requesting priority. Hence the incremental cost of installing bus priority at signals is much lower than with the existing system and the location of detection points is more flexible (www.tfl.gov.uk).
References
Diebold Institute of Intelligent Transport Systems 1995, Transportation
Infostructures: The Development of Intelligent Transportation Systems, Praeger, Westport CT.
Selective Vehicle Detection 2006, Transport for London, viewed 11 January,
2008, <http://www.tfl.gov.uk/assets/downloads/businessandpartners/svd- brochure-2006.pdf>.
The Way Ahead for London’s Bus Priority at Traffic Signals, Traffic for Lonndon,
viewed 11 January, 2008, <http://www.tfl.gov.uk/assets/downloads/TfL- bus-signals-priority.pdf>.
White, P 2002, Public Transport: Its Planning, Management, and Operation,
Spon Press, London.
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