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Bus rapid transit
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Bus rapid transit (BRT) is a broad term given to a variety of transportation systems that, through improvements to infrastructure, vehicles and scheduling, attempt to use buses to provide a service that is of a higher quality than an ordinary bus line. Each BRT system uses different improvements, although many improvements are shared by many BRT systems. The goal of such systems is to at least approach the service quality of rail transit while still enjoying the cost savings of bus transit.
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Bus rapid transit (BRT) is a broad term given to a variety of transportation systems that, through improvements to infrastructure, vehicles and scheduling, attempt to use buses to provide a service that is of a higher quality than an ordinary bus line. Each BRT system uses different improvements, although many improvements are shared by many BRT systems. The goal of such systems is to at least approach the service quality of rail transit while still enjoying the cost savings of bus transit. The expression BRT is mainly used in North America; in Europe and Australia, it is often called a busway, while elsewhere, one may speak of quality bus or simply bus service while raising the quality.
Etymology
Bus rapid transit takes part of its name from rapid transit which describes a high-capacity rail transport system with its own right-of-way, its alignment often being elevated or running in tunnels, and typically running long trains at short headways of a few minutes. Because of the name similarity one tends to associate the merits of rapid transit also with the newer BRT expression. BRT encompasses a broad variety of modes, including those known or formerly known as express buses, limited busways and rapid busways and even BHNS in France (Bus à Haut Niveau de Service).
Ironically, the term bus rapid transit does not refer to the speed of BRT buses. Typical transit speeds of BRT systems range from 12 to 30 miles per hour (19 to 48 km/h) which compares well with surface running LRT.
Main features
These bus systems can come in a variety of forms, from dedicated busways that have their own rights-of-way (e.g., the Ottawa Transitway or the Pittsburgh MLK East Busway) to bus services that utilize HOV lanes and dedicated freeway lanes (e.g., Honolulu's CityExpress) to limited stop buses on pre-existing routes.
An ideal bus rapid transit service would be expected to include most of the following features:
- Bus only, grade-separated (or at-grade exclusive) right-of-way : The main feature of a BRT system is having dedicated bus lanes which operate separate from all other traffic modes. This allows buses to operate at a very high level of reliability since only professional motorists are allowed on the busway. A side benefit of this are lower construction costs since busways can be engineered to tighter standards and still remain safe compared to a roadway open to non-professional drivers.
- Such a right of way may be elevated; on rare occasions, the right of way may be a modified rail right of way.
- A bus street or transit mall can be created in an urban center by dedicating all lanes of a city street to the exclusive use of buses.
- Low-cost infrastructure elements that can increase the speed and reliability of bus service include bus turnouts, bus boarding islands, and curb realignments.
- Comprehensive coverage : In addition to using dedicated busways, BRT's can also take advantage of existing roadways in cities that already have a comprehensive road network for private automobiles. Service can be made more time efficient and reliable than a standard bus system by taking advantage of bus priority methods.
- Serves a diverse market with high-frequency all day service : A BRT network with comprehensive coverage can serve a diverse market (all income ranges) by moving people from their current location to their destination with high frequency and reliability while maintaining a high level of customer experience. As with any transit system, if any of these benefits are taken out of the equation, or do not provide better service than other modes of transit, the network will not be able to serve as diverse a market or offer high-frequency service without heavy subsidy.
- Bus priority / bus lanes : Preferential treatment of buses at intersections can involve the extension of green time or actuation of the green light at signalized intersections upon detection of an approaching bus. Intersection priority can be particularly helpful when implemented in conjunction with bus lanes or streets, because general-purpose traffic does not intervene between buses and traffic signals.
- Vehicles with tram-like characteristics
Recent technological developments such as bi-articulated buses and guided buses have benefited the set up of BRT systems. The main developments are:
- Improved riding quality (guided bus, electronic drivetrain control smoothing the operation),
- Increased capacity (bi-articulated or double decker),
- Reduced operating costs (hybrid electric power train).
- A specific image with a brand name : (Viva, Max, TransMilenio...) and specific stations with state of the art features, automatic vending machines...
- Off-bus fare collection : Conventional on board fare collection slows the boarding process, particularly when a variety of fares are collected for different destinations and/or classes of passengers. An alternative would be the collection of fares upon entering an enclosed bus station or shelter area prior to bus arrivals (similar to fare collection at a kiosk prior to entering a subway system). This system would allow passengers to board through all doors of a stopped bus.
- Level boarding : Many BRT systems also use low floor buses (or high level platforms with high floor buses) to speed up passenger boardings and enhance accessibility.
- Stations : High quality BRT systems often feature significant investment in enclosed stations which may incorporate attractive sliding glass doors, staffed ticket booths & information booths, and other more standard features listed above. This style of station is seen in Bogota's TransMilenio and in some other cities in Latin America that have adopted BRT systems, while most North American systems tend to use open platform stops, or shelter-style platform stops.
Acceptance of BRT may increase using trolley-buses, because of the lower gaseous and noise emissions. The price penalty of installing overhead lines can be repaid over a longer period by the savings from centrally generated electricity.
Controversies
Opponents of BRT initiatives claim that it is not an effective replacement for light rail or subway services. They argue that in order to optimize the efficiency, it needs its own right-of-way, which requires additional space and construction costs. A regular bus service would share the road with cars; a BRT service operating in mixed traffic would be subject to the same congestion and delays as do ordinary city buses. Furthermore, signal priority systems, which are often the sole factor differentiating BRT from regular limited-stop bus service (most notably in Los Angeles's extensive "Rapid" system), might cause severe disruptions to traffic flow on major cross streets. Opponents argued that this merely redistributes, rather than reduces, the traffic congestion problems that BRT systems are designed to alleviate. On the other hand, many light rail systems also utilize signal priority system and railroad-style crossing gates (with long cycle times) to speed up service as well, and in the same time both BRT and light rail get more persons across a road junction than car traffic.
Comparison with other forms of mass transit
BRT attempts to combine the advantages of a metro system (noticeably right-of-way which improves punctuality and frequency) with the advantages of a bus system (low construction and maintenance costs, right-of-way not required for entire length, and if catered for the ability for feeder bus services to join a trunk busway).
Compared to standard bus service BRT systems with dedicated right-of-way lanes, and thus an increased average vehicle speed, can provide more passenger miles with the same number of vehicles and personnel. They also bring about a smoother ride than a normal bus immersed in stop-and-go traffic.
It is overly simplistic to use calculations to predict the capacity of BRT and normal buses and say typical buses are 12 metres (40 feet) long, articulated buses 18 metres (60 feet). The maximum length for a street-running tram (in Germany) is 75 meters (about 250 feet). Light rail systems running in-street are limited to one city block in length, unless (as in Sacramento, CA) they are allowed to obstruct intersections when stopped. Metro trains can be 240 m (about 800 feet) long.
With similar dwell times in stations the capacity of rail systems would scale with the length of the train. For instance, a light rail system running on two-minute headways with 200-passenger cars operating as single units could carry 6,000 passengers per hour. It should theoretically therefore carry 12,000 passengers per hour with two-car trains, and 24,000 per hour with four-car trains. In practice real world delays multiply and headways become disrupted causing a practical limitation of around 12,000 to 19,000
However, the Transmilenio system in Bogotá, reports to carry 2'850.000 passengers per day on average, including feeder lines. This would put it in 8th place in the world list of Metro systems by annual passenger rides. Transmilenio, during 2008, is in its third of seven projected construction phases. The Transportation Research Board reports that the 388 kilometer complete system is projected to cost U$3.3 billion, which is only 10 percent more than a previously proposed Metro of 30 kilometers would have cost.
Comparison with light rail
Studies that count individual passengers by observation is a notable source of information regarding capacity. A survey by the UK Transport Research Laboratory revealed:
Exhibit 3-22: Maximum Observed Peak Hour Bus Flows, Capacities, and Passenger Flows at Peak Load Points on Transitways
Measured Peak Hour Passenger Flow (Passengers / Hour)
Designated Lane: Ankara, Istanbul, Abidjan 7,300 – 19,500
Designated Lanes with Feeders Curitiba, Brazil 13,900 – 24,100
Designated Lanes with Bus Ordering (Travelling in Clusters) Porto Alegre 17,500 – 18,300
Designated Lanes with Overlapping Routes, Passing at Stations and Express Routes
Belo Horizonte, São Paulo 15,800-20,300
Bogotá 35,000-40,000
However, many BRT systems such as OC Transpo Transitway, Ottawa and South-East Busway, Brisbane are based on multiple bus routes sharing a common dedicated busway to bypass congestion, especially to/from a central business district. In this form, the BRT system passenger capacity is limited by vehicle capacity times vehicle headway of the busway. As buses can operate at headways as low as 10 seconds between vehicles (compared to at least one minute headways for rail vehicles), actual busway capacity can reach passenger rail capacities. At the high end, the Lincoln Tunnel XBL bus lane carries 62,000 commuters in the 4 hour morning peak, more than any Light Rail Line. However, this lane has no stops in it. Stops increase the headway and limit a BRT lane to about 10,000 passengers per hour, even with passing lanes in the stations. Note that this is still five times the number carried in the automobiles in a congested freeway lane. At it's busiest point, Brisbane's South-East Busway currently carries in excess of 15,000 commuters per hour per direction, and is not yet considered at capacity.
Many agencies make a clear distinction between a pure BRT, which is in exclusive lanes, and a more compromised form in mixed traffic. For example, the Los Angeles Orange Line runs entirely in an exclusive lane and therefore achieves speed and reliability comparable to rail. Because it is functionally equivalent to rail, the Los Angeles County Metropolitan Transportation Authority presents this line as part of its rail transit system, distinct from its "Rapid" lines, which run in mixed traffic.
The typical diesel engine on the bus causes noticeable levels of air pollution, noise and vibrations. Through developing buses as hybrid vehicles and the use of new forms of trolleybus BRT designers hope to increase ride quality and decrease pollution. As the energy use for acceleration is proportional to the vehicle mass, electric traction allows lighter vehicles, faster acceleration and energy that can be fed back into batteries or the grid through regenerative brakes. Regenerative braking is standard on modern rail systems.
In contrast to BRT, both Light Rail and rapid transit require the placement of rails for the whole line. The tram usually avoids the high additional costs for the engineering structures like tunnels that need to be built for metros. Rail tends to provide a smoother ride and is known to attract significantly higher passenger numbers than road-based systems.
Many BRT designers have used the need to construct power conduit systems as an argument against Light Rail, but a new proposal, known as ultra light rail, would have trams carry their own power, much like a bus, at a significant energy savings due to lack of rolling resistance.
In larger towns and cities, such as Essen, Germany and Pittsburgh, U.S., it is common for a right of way exclusive to public transport to be used by both light rail and buses.
In tunnels or tunnel systems
A special issue arises in the use of bus vehicles in metro structures. Since the areas where the demand for an exclusive bus right-of-way is apt to be in dense downtown areas where an above-ground structure may be unacceptable on historic, logistic, or environmental grounds, use of BRT in fully underground tunnels may not be avoidable.
Since buses are usually powered by internal combustion engines, bus metros raise ventilation issues similar to those of tunnels. In the case of tunnels, powerful fans typically exchange air through ventilation structures on the surface, but are usually placed in a location as remote as possible from occupied areas to minimize the effects of noise and concentrated pollution.
A straightforward way to deal with this is to use electrical propulsion in tunnels and, in fact, Seattle in its Metro Bus Tunnel and Boston in Phase II of its Silver Line are using this method in their respective BRTs. In the case of Seattle, dual-mode (electric/diesel electric) buses manufactured by Breda were used until 2004, with the center axle driven by electric motors obtaining power from a trolley wire through a trolley pole in the subway, and with the rear axle driven by a conventional diesel powertrain on freeways and streets. Boston is using a similar approach, after initially using electric trolleybuses to provide service pending delivery of the dual mode vehicles in 2005. In 2004, Seattle replaced its "Transit Tunnel" fleet with diesel-electric hybrid buses, which operate similarly to hybrid cars outside the tunnel and in a low-noise, low-emissions "hush mode" (in which the diesel engine operates but does not exceed idle speed) when underground.
The necessity for providing electric power in these environments brings the capital and maintenance costs of such routes closer to light rail and raises the question of building light rail instead. In Seattle, the downtown transit tunnel retrofitted for conversion to a shared hybrid-bus and light-rail facility in preparation for Seattle's Central Link Light Rail line to be operating in 2009.
List of systems
Implementation by country
See also
* Bus lane
External links
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- WestStart-CALSTART program, in partnership with the FTA).
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