eventually converting to light rail. In Seattle, the downtown transit tunnel was retrofitted for conversion to a shared hybrid-bus and light-rail facility in preparation for Seattle's Central Link Light Rail line, which opened in July 2009. In March 2019, expansion of the light rail in the tunnel moved busses back to surface streets. Bi-articulated battery electric buses cause no problems in tunnels anymore but provide BRT capacity. Performance A BRT system can be measured by a number of factors. The BRT Standard was developed by the Institute for Transportation and Development Policy (ITDP) to score BRT corridors, producing a list of rated BRT corridors meeting the minimum definition of BRT. The highest rated systems received a "gold" ranking. The latest edition of the standard was published in 2016. Other metrics used to evaluate BRT performance include: The vehicle headway is the average time interval between vehicles on the same line. Buses can operate at headways of 10 seconds or less, but average headways on TransMilenio at busy intersections are 13 seconds, 14 seconds for the busiest section of the Metrobus (Istanbul), 7 seconds in Belo Horizonte, 6 seconds in Rio de Janeiro. Vehicle capacity, which can range from 50 passengers for a conventional bus up to some 300 for a bi-articulated vehicle or 500. The effectiveness of the stations to handle passenger demand. High volumes of passengers on vehicles require large bus stations and more boarding areas at busy interchange points. This is the standard bottleneck of BRT (and HRT). The effectiveness of the feeder system: can these deliver people to stations at the required speed? Local passenger demand. Without enough local demand for travel, the capacity will not be used. Based on this data, the minimum headway and maximum current vehicle capacities, the theoretical maximum throughput measured in passengers per hour per direction (PPHPD) for a single traffic lane is some 150,000 passengers per hour (250 passengers per vehicle, one vehicle every 6 seconds). In real world conditions BRT Rio (de Janeiro, BRS Presidente Vargas) with 65.000 PPHPD holds the record, TransMilenio Bogotá and Metrobus Istanbul perform 49,000 – 45,000 PPHPD, most other busy systems operating in the 15,000 to 25,000 range. Research of the Institute for Transportation and Development Policy (ITDP) shows a capacity ranking of MRT modes, based on reported performance of 14 LRT systems, 14 HRT systems (just 1-track + 3 2-track-systems "highest capacity") and 56