High Quality Content by WIKIPEDIA articles! Key bus routes of the Massachusetts Bay Transportation Authority (MBTA) system are 15 routes that have high ridership and higher frequency standards than other bus lines, according to the 2006 MBTA Service Policy. These key bus routes ensure basic geographic coverage of frequent service in the densest areas of the city and connect to other MBTA services that have access to other areas throughout the region. In November 2006, the MBTA launched a concerted effort to improve service quality on these routes, which has been completed. The 2008 Service Plan recommended improvements for various lines, including upgrading the 31 bus to Key Route standards. A second round of improvements, entitled the Key Routes Improvement Project is being funded by the American Recovery and Reinvestment Act of 2009.