Bus rapid transit

Taxonomy and description

According to Levinson et al (2003, p12) Bus Rapid Transit (BRT) is “a flexible, rubber-tired rapid-transit mode that combines stations, vehicles, services, running ways, and Intelligent Transportation System (ITS) elements into an integrated system with a strong positive identity that evokes a unique image.”   Similarly, Wright and Hook have pointed out that BRT “is a high-quality bus based transit system that delivers fast, comfortable, and cost-effective urban mobility through the provision of segregated right-of-way infrastructure, rapid and frequent operations, and excellence in marketing and customer service.”  (Wright and Hook, 2007: p11).

Levinson et al (2003) give the following seven identifying characteristics of a bus system that constitute a BRT system (Table 1)

Source: Levinson et al (2003) p 13.

From Table 1, it is clear that BRT is intended to integrate all these component elements and technology to provide a high quality public transport package.  All these various elements are intended to reduce the total journey time associated with a bus journey and to provide an improved level of service over conventional bus services. Provision of individual elements on their own does not generally qualify the system as a Bus Rapid Transit (Wright and Hook, 2007).

Design of the right of way

There are two primary forms of providing the required level of segregation required for operation of the bus services:

1. By means of providing an exclusive lane.
2. By utilising Guided Bus Systems.

However the provision of bus lanes or guideways alone will not qualify the system as a BRT system.  Figure 1 shows the spectrum of BRT systems and the primary distinction between conventional bus services to a full BRT system.

Figure 1: Quality Spectrum of BRT
Source: Wright and Hook (2007 p12)

Technology

In this summary of the technological options for guided bus systems, the focus is primarily on guided systems since information on bus lanes and bus ways can be found under a separate note on bus priorities.

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, making it 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 Systems

Whilst kerb guidance is the most commonly used system, there is 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.

Automatic 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, 2002).

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. Schemes are in operation in the Netherlands and Spain.

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 arisen (Bain, 2002), and the technology has now been withdrawn.
There are two aspects to the technology of kerb guided bus: the guideway itself and the on-bus equipment.
The guideway – With Kerb Guided Systems, 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 tracks.