advisories that may affect one's current trip. Transit and Moovit are examples of apps that are available in many cities around the world. Some operators of bus rapid transit systems have developed their own apps, like Transmilenio. These apps even include all the schedules and live arrival times and stations for buses that feed the BRT, like the SITP (Sistema Integrado de Transporte Público or Public Transit Integrated System) in Bogotá. In tunnels or subterranean structures A special issue arises in the use of buses in metro transit structures. Since the areas where the demand for an exclusive bus right-of-way are 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 tunnels may not be avoidable. Since buses are usually powered by internal combustion engines, bus metros raise ventilation issues similar to those of motor vehicle tunnels. Powerful fans typically exchange air through ventilation shafts to the surface; these are usually as remote as possible from occupied areas, to minimize the effects of noise and concentrated pollution. A straightforward way to reduce air quality problems is to use internal combustion engines with lower emissions. The 2008 Euro V European emission standards set a limit on carbon monoxide from heavy-duty diesel engines of 1.5 g/kWh, one third of the 1992 Euro I standard. As a result, less forced ventilation will be required in tunnels to achieve the same air quality. Another alternative is to use electric propulsion, which Seattle's Metro Bus Tunnel and Boston's Silver Line Phase II implemented. In 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 trolley wires through trolley poles 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 trolleybuses 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 need to provide electric power in underground environments brings the capital and maintenance costs of such routes closer to those of light rail, and raises the question of building or