Alameda-Contra Costa Transit District (AC Transit)

AC Transit (in full, Alameda-Contra Costa Transit District) is a regional bus agency serving parts of Alameda County and Contra Costa County in the western coastal area of the East Bay of the San Francisco Bay Area. In addition, AC Transit runs "Transbay" routes across San Francisco Bay to the city of San Francisco, and selected areas in San Mateo County and Santa Clara County.

AC Transit is constituted as a special district under California law. It is governed by seven elected members (five from geographic wards and two at-large). It is not a part of the Alameda or Contra Costa county governments, although the initials "AC" are often mistaken to mean "Alameda County."

The district is the public successor to the privately owned Key System.

NTD Code: 9014