Southeastern Pennsylvania Transportation Authority

The Southeastern Pennsylvania Transportation Authority, SEPTA for short, is a regional quasi-public state agency that operates bus, subway, commuter rail, trolley (streetcar), and trackless trolley service in the Philadelphia, Pennsylvania area.

The city transit system was formerly owned and operated by the Philadelphia Transportation Company (known as the PTC) until 1968, and before that the Philadelphia Rapid Transit Company (the PRT). The region's suburban bus and trolley lines were operated by the Philadelphia Suburban Transportation Company (also called the Red Arrow Lines), the Schuylkill Valley Lines, and a handful of other smaller companies into the 1970s.

Subway Service

The city's two subway lines are:

• The Market-Frankford Subway-Elevated (also known as the "El" or the "Blue Line," abbreviated "MFSE" or "MFL"), which runs from 69th Street Terminal in Upper Darby, adjacent to West Philadelphia, to the neighborhood of Frankford, in Northeast Philadelphia. The Market-Frankford line is sometimes called the "El" because two large sections of the line run above street level, connected by a stretch of subway beneath the downtown (Center City), University City, and part of West Philadelphia. The "El" connects with the PATCO High-Speed Line to Camden and the New Jersey suburbs at the 8th Street station (additional fare required for transfer).

• The Broad Street Subway (also known as the "Orange Line", abbreviated "BSS"), which runs from Fern Rock Station in the extreme northern reaches of the city to Pattison Avenue in South Philadelphia.

• A spur of the Orange Line, known as the Broad-Ridge Spur, runs from Fern Rock station (north of City Hall) to a hub at 8th and Market Streets, where it links to the Blue Line. As mentioned, connection to the PATCO High-Speed Line is available here.

The two lines intersect at Philadelphia City Hall, where a free interchange exists which includes the "Green Line" ("subway-surface" trolley line). See also the List of Philadelphia subway stations.

Norristown High Speed Line

The Norristown High Speed Line (NHSL), designated as Route 100 of the Suburban Transit Division, is a hybrid between light rail and heavy rail operating between Norristown Transportation Center and 69th Street Terminal, running entirely on its own right of way, inherited from the Philadelphia and Western Railroad, an interurban railroad. The line is unique in its combination of transportation technologies. It has full grade separation, third rail power collection, and high-level platforms common to heavy rail systems, but has small vehicles, onboard fare collection, and frequent stops more common to light rail systems.

See also the list of stations on the Norristown High Speed Line.

Regional Rail Lines

SEPTA also operates a number of trains, known as the Regional Rail Lines to and from places in the metropolitan area. All seven of them pass through 30th Street Station, Suburban Station, and Market East Station in Center City, as well as a stop on the campus of Temple University, as part of their route. The regional lines run on former Pennsylvania Railroad and Reading Railroad tracks. Lines of the Pennsylvania Railroad ended at Suburban Station, while the lines of Reading Railroad ended at Reading Terminal.

• The R1 line runs from Philadelphia International Airport to Glenside.

• The R2 line runs from Newark, Delaware to Warminster.

• The R3 line runs from Elwyn to West Trenton station in Ewing, New Jersey.

• The R5 line runs from Doylestown to Thorndale. The segment of this line between Center City and Thorndale was known as the "Main Line" in the Pennsylvania Railroad's time, and became the namesake of the affluent Philadelphia suburb of the same name.

• The R6 line runs from Norristown to Bala Cynwyd.

• The R7 line runs from eastern Chestnut Hill to Trenton, New Jersey. This line offers an inexpensive connection to New York Penn Station via New Jersey Transit's Northeast Corridor Line.

• The R8 line runs from Fox Chase to western Chestnut Hill.

- an extremely detailed guide to SEPTA's Regional Rail system.

The R4 Line

SEPTA's regional lines are numbered R1 to R8, with the R4 missing. Originally, when SEPTA was planning its regional lines after opening the tunnel through Center City, an R4 line was planned to run from Fox Chase to Bryn Mawr on the R5 Paoli line. This followed the pairing recommendations of University of Pennsylvania professor Vukan Vuchic. R4 trains were to run local to Bryn Mawr while R5 trains (paired with the Lansdale to Doylestown line.) would run express to Bryn Mawr and then further west.

These pairings were possible because of the Swampoodle Connection, a connecting track planned between SEPTA's former Reading Company line to Norristown and its former Pennsylvania Railroad line to Chestnut Hill. This connection would have allowed the "Chestnut Hill West" line to be numbered R3 and connected to the former Pennsylvania Railroad line to Media and West Chester via Center City. When the connection was not built, the Chestnut Hill West line was on the wrong side of the system to be through-routed to West Chester, and it was paired instead with trains to Fox Chase as the R8. The R3 designation now used for the line to West Trenton station was originally R1 under the Vuchic plan and paired with trains to the airport.

Several expansion plans have proposed using the R4 designation for a new line.