Bus rapid transit (BRT)* is commonly defined as a bus transit system that makes extensive use of dedicated lanes, has off-board fare collection and has priority at traffic signals. It is designed to have greater speed and capacity than conventional bus lines that run in streets together with other traffic. The buses are most commonly conventional buses that operate using internal combustion engines, although on some systems they are powered by electricity obtained from on-board batteries or overhead trolley wires.
However, bus rapid transit contrasts greatly with true rapid transit, which consists of electrically powered trains that operate on steel rails on exclusive rights of way which are completely separated from streets, usually by tunnels and elevated structures.
Thus, bus rapid transit is more similar to light rail, which likewise operates in mostly dedicated lanes but sometimes in ordinary traffic and often has some priority at traffic signals, although BRT often maintains stricter lane exclusivity than many mixed-traffic light rail systems. The major differences are that light rail vehicles run on steel rails, are typically larger than buses and are commonly coupled together to form trains.
Bus rapid transit can be an excellent way of improving urban transportation quickly and at minimal cost. This is true not only for smaller cities and lower density areas of larger cities, but also for high-density areas in lower-income countries with limited construction budgets and abundant labor. It can play an important role in achieving the dual goals of improving urban mobility and reducing the environmental harm from automobile traffic.
Not requiring extensive sections of tunnels and elevated structures greatly reduces the cost of system construction as compared with rapid transit and also eliminates the use of massive amounts of concrete and steel, with their massive carbon footprints. Moreover, the trend towards using electric buses on new BRT systems further contributes to protecting the environment by completely eliminating toxic emissions in urban centers.
Additional expenses beyond those of conventional urban bus systems to maximize the passenger experience and thus encourage use can include adding or enhancing passenger shelters at bus stops, providing real-time information systems for passengers, adding wifi, adding signal priority at intersections and repainting vehicles to emphasize the improved service. Costs per passenger can be reduced as a result of more passengers per vehicle and higher speeds.
Despite the benefits of BRT as a low cost and quick-to-implement means of improving urban transportation and promoting modal shift, there are many situations in which light rail or rapid transit can be superior alternatives. Among the factors favoring rail solutions include greater capacity, lower labor costs per passenger, reduced energy consumption, substantially longer vehicle lifespans, reduced noise and increased passenger comfort (e.g., more spacious interiors and smoother rides).
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*Some critics argue these systems should be called "enhanced bus service" to avoid causing confusion and diluting the definition of rapid transit. However, the transit industry uses the high-profile "bus rapid transit" label mainly for psychological reasons, as it enhances the status of bus services and thus increases the political will and funding prospects for transit upgrades at a fraction of the cost of building true rapid transit. This is a prime example of "semantic inflation," which has become increasingly common regarding environmental and transportation issues.