Guided bus systems provide a lower cost alternative to light
rail while having the advantages of dedicated rights of way. While
totally separate rights of way can be provided, as in Adelaide, most current
proposals envisage providing guideways solely where buses need to bypass
congestion, as in Leeds. This can be achieved with minimal space requirements;
the guideway need only be 3m wide, and is only needed in the direction
in which congestion is experienced. Specially equipped buses can then
operate normally on the rest of their routes, hence providing much more
extensive suburban coverage than light rail (Read, Allport and Buchanan,
1990). They have a number of objectives, including to increase the reliability,
speed and accessibility of bus services, to reduce road congestion through
the diversion of car journeys to bus and to generate increased revenue
through increased bus-use.
Guided bus systems involve taking the steering of the bus off the bus
and away from the bus driver for all or, more usually, part of the route.
In doing so, they eliminate the need to allow for any lateral movement
of the bus within a lane of traffic. A bus is generally approximately
2.5m wide, but a bus lane is usually 3.75m or even 4m wide to allow for
this lateral movement. A guided bus system, therefore, provides opportunities
to implement dedicated busways where road space is in short supply and,
hence, where conventional bus lanes could be impractical. Depending upon
the guidance technology used, systems may also provide opportunities to
improve physical access to the bus by minimising the vertical and horizontal
gaps between the bus stop and the bus. Some systems also provide for physical
segregation from other traffic, meaning that it is impossible for other
vehicles to block the guideway. They also provide for considerable flexibility
in operations, in that a suitably adapted bus can travel on a guideway
where this is available but can also travel on any other part of the road
network as required.
Types of Guided Bus System
kerb guidance is the most commonly used system, there are a range of systems
available or in development:
Kerb guided Systems - to date, this is the most commonly used guidance
technology. Specially equipped buses, with small 'guidewheels' positioned
in front of the main front wheels, are guided along a track formed out
of two vertical upstands (or kerbs), separated by the width of a bus axle
(approximately 2.5m). On entering the track (or guideway), the guidewheels
connect with the kerbs and guide the bus.
Electronic Guidance Systems - specially adapted buses may be guided electronically
via underground cables which transmit signals to the vehicle (as with
the electronically guided Mercedes service vehicles operating in the Channel
Tunnel). However, a recent investigation of this form of guidance system
raised a number of safety concerns (Bain, 2004);
Optical guidance - this is a more recent development in guidance technology
and involves dashboard- mounted cameras, a video- monitoring system and
a road- marking recognition system. Field trials of such a system took
place in 2001 under the CIVIS project and there are plans to implement
a test scheme in Las Vegas.
Other guided bus systems include the Translohr vehicle, which uses two
front rollers running on a central guideway to steer the vehicle, and
Bombardier's low floor guided light tram, for which automatic vehicle
guidance is effected via small metal wheels which run in a central groove
in the pavement. However, in the two instances where guided light tram
has been implemented - in Caen and Nancy - safety concerns regarding the
transfer from automatic guidance to manual steering have resulted in the
systems being closed pending a technical enquiry (Bain, 2004).
There are two aspects to the technology of kerb guided bus: the guideway
itself and the on-bus equipment.
The guideway - Typically, the guideway has two tracks along which the
bus' wheels run. These tracks are typically made from reinforced concrete
as the wear resulting from the wheel path being exactly the same each
and every time would erode other surfaces, eg tarmac, much more quickly.
At the outer edge of each of the two tracks is a vertical kerb. The two
kerbs provide the guidance to the bus and are set 2.6m apart from one
another. A drainage channel of approximately 1.2m runs between the two
The on-bus equipment - The only equipment required to modify a standard
bus, with standard steering, for operations along the guideway are the
guidewheels. The guidewheels use 180mm solid rubber tyres and are positioned
in front of the main front wheels of the bus. They are installed via a
J beam which is bolted to the back of the front wheel assembly and protrude
5cm out from the edge of the bus on each side.
Text edited at the Institute for
Transport Studies, University of Leeds, Leeds LS2 9JT