BOSTON -- Boston's public transportation system, the Massachusetts Bay Transportation Authority or MBTA, is the oldest and fourth largest in the nation.

The city first used omnibuses back in the 1820s that were pulled by horses. Eventually, tracks were laid through rutted, bumpy streets for the buses to ride on and in 1856 the first horsecar line started operating from Central Square, in Cambridge, to the West Boston Bridge to Bowdoin Square.

Transit authorities later decided to electrify the system and, according to the MBTA's Web site, "the first electric streetcar line here in the 'Hub' began operation on Jan. 1, 1889 starting from the Allston Railroad Depot, up Harvard Avenue, left at Coolidge Corner to Boston's Park Square. The present MBTA's Green Line/Beacon Street was part of this first installation."

Streetcar congestion soon became so great that the state authorized a commission to study the next phase. They recommended a system that would cover most towns within a 10-mile radius of the State House, which included 27 communities. The commission came up with a plan for four elevated railway lines and a tunnel under Tremont Street for streetcars. It also authorized the creation of the Boston Elevated Railway Company (BERY).

The "El," as the system soon came to be known, invented the idea of the "articulated" streetcar line, a series of cars that would bend around the city's narrow, twisting streets.

The "El" began to experience financial difficulties because of an enforced 5 cent fare and ridership declines. In 1918, the decision was made by the state to provide public transportation at reasonable rates.

In 1947, the Metropolitan Transit Authority was created by the Legislature to run the system. It became the Massachusetts Bay Transportation Authority in 1964, "one of the first combined regional transportation planning and operating agencies to be established in the United States," according to the MBTA Web site.

The MBTA says, in terms of daily ridership, it remains the nation's fifth-largest mass transit system.

It serves a population of 4,667,555 (2000 census) in 175 cities and towns with an area of 3,244 square miles.

To carry out its mission, the MBTA maintains 183 bus routes, two of which are Bus Rapid Transit lines, three rapid transit lines, five streetcar (Central Subway/Green Line) routes, four trackless trolley lines and 13 commuter rail routes.

The average weekday ridership for the entire system is approximately 1.1 million passenger trips.