Ottawa's city limits had been increasing over the years, but it acquired the most territory on 1 January 2001, when it amalgamated all the municipalities of the Regional Municipality of Ottawa–Carleton into one single city. Regional Chair Bob Chiarelli was elected as the new city's first mayor in the 2000 municipal election, defeating Gloucester mayor Claudette Cain. The city's growth led to strains on the public transit system and road bridges. On 15 October 2001, a diesel-powered light rail transit (LRT) line was introduced on an experimental basis. Known today as the Trillium Line, it was dubbed the O-Train and connected downtown Ottawa to the southern suburbs via Carleton University. The decision to extend the O-Train, and to replace it with an electric light rail system, was a major issue in the 2006 municipal elections, where Chiarelli was defeated by businessman Larry O'Brien. After O'Brien's election, transit plans were changed to establish a series of light rail stations from the east side of the city into downtown, and for using a tunnel through the downtown core. Jim Watson, the last mayor of Ottawa prior to amalgamation, was re-elected in the 2010 election.