At 32nd Street, the tunnel carrying the Subway-Surface lines joins the MFL tunnel. The MFL tracks are in the center and the trolley tracks are on the outside. 30th Street station consists of an island platform between the two innermost tracks for Market–Frankford Line trains, and outboard "wall" platforms for Subway–Surface route 10, 11, 13, 34, and 36 trolleys. After passing beneath the Schuylkill River, the next stop to the east for Market–Frankford Line trains is at 15th Street; Subway-Surface trolleys also have stations at 22nd Street and 19th Street. 15th Street is the central interchange station for the MFL, Subway-Surface trolleys, and Broad Street Line. The Subway-Surface tracks end in a loop beneath Juniper Street at Market just after crossing above the Broad Street Line. The Juniper Street platform connects to 13th Street station on the MFL.
Though it now tunnels in a straight line directly beneath Philadelphia City Hall, prior to 1936, the original MFL trackage between 15th and 13th Street stations separated and went around the sides of City Hall (eastbound trains around the south side, westbound trains around the north side). Parts of that original alignment can still be seen from subway-surface cars as they pass around the south side of City Hall en route to Juniper Street station. The Market Street tunnel continues east to Front Street and then turns north, where it rises in the median of I-95. The rail line and freeway share an elevated embankment for about ½ mile (0.8 km), including Spring Garden station (which replaced Fairmount station on the Frankford Elevated). The line then heads under the southbound lanes and over Front Street on an elevated structure that turns northeast onto Kensington Avenue, which merges with Frankford Avenue, which the line follows to its end. Just north of Bridge Street, a quick curve to the north brings the line to its terminus at the Frankford Transportation Center.
In FY 2005, 25,220,523 passengers rode the Market-Frankford Line. Its weekday average ridership of 178,715 made it the busiest line in the entire SEPTA system. The Market–Frankford Line required 142 vehicles at peak hours, cost $86,644,614 in fully allocated expenses, and collected $54,309,344 in passenger revenues, for an impressive farebox recovery ratio of 63 percent.
On February 11, 2008, SEPTA expanded the morning and afternoon weekday service with off peak trains running every six minutes instead of every eight minutes. It represents a 12% increase in MFL Service through the day.
Extensions took the line east to 2nd Street on August 3, 1908, and via several curves to the Delaware River between Market Street and Chestnut Street on September 7, 1908. The Delaware Avenue Elevated (also called the Ferry Line, because of the multiple ferries across the river) opened on October 4, 1908, as a further extension south along the river to South Street. The only two stations on this extension were Market–Chestnut and South Street.
The Frankford Elevated opened on November 5, 1922, with trains from 69th alternating between Frankford and the Ferry Line. In 1937, operations were changed to use the Ferry Line only during the day and not at all on Sunday. In 1939 the line to the ferries was closed and the structure was demolished. The old interlocking tower and stub remains of the junction with the Ferry Line survived until the realignment into the median of I-95 in the 1970s.
A new section of tunnel from 22nd Street, where the Market–Frankford line started rising towards the Schuylkill River, to 32nd Street was built in the 1930s as part of a program of railroad improvements undertaken by the City of Philadelphia and the Pennsylvania Railroad, but funding ran out before the subway extension was complete. Construction resumed in 1947, and the current configuration opened on November 6, 1955. The old elevated structure was removed by June 20, 1956. In addition to extending the Market Street subway tunnel west to 44th Street, with new stations at 30th, 34th and 40th streets, a new trolley tunnel was built under Market, Ludlow and 36th streets and the former Woodland Avenue, leading to a new western portal at 40th Street for routes 11, 13, 34 and 36 (route 10 trolleys use a portal at 36th and Ludlow). New stations for the trolleys were constructed at 22nd, 30th, 33rd (between Market and Ludlow), 36th (at Sansom), and 37th (at Spruce) streets. The 24th Street trolley station and tunnel portal was abandoned.
Skip-stop operation began on January 30, 1956. In the original skip-stop configuration, in addition to the A and B stops shown on the map above, 2nd and 34th Street were "A" stations, and Fairmount (replaced by Spring Garden) was a "B" station; the A and B designations at these stations were changed to "All-Stop" because of increased patronage in the 1990s. As I-95 was built through Center City Philadelphia in the late 1970s, part of the Frankford El was relocated to I-95's median, and the Fairmount station was replaced with Spring Garden, on May 15, 1977.
SEPTA has completed, in 2003, replacement of the old Bridge-Pratt terminal with a new $160,000,000 Frankford Transportation Center located on private right-of-way.
Currently, SEPTA is undertaking a $567,000,000 complete reconstruction of the Market Street Elevated between Millbourne and the 44th Street portal. The new Market Street Elevated, consisting of a center-pillar viaduct, will allow PennDOT to widen Market Street to four lanes without having elevated supports impeding the flow of traffic between 63rd Street and 44th Street. The project has already reconstructed 46th Street, 52nd Street, 56th Street, 60th Street, and Millbourne stations, and also includes the ongoing reconstruction of 63rd Street station. The construction is slated for completion in 2009.
As with many other rail lines, the signal system on the Market–Frankford Line has progressed from the original lineside block signals using semaphores, to three-aspect Type D color light (green, over yellow, over red) signals, to cab signalling, eliminating the lineside block signals.
The SEPTA fleet for the Market–Frankford line consists of 220 M-4 rail cars, with seating for 49 and standing room for 55, each costing $1.29 million
The M-4 cars, manufactured by AdTranz, were brought into service in 1997 to replace the M-3 "Almond Joy" stock, so called because of their distinctive ventilation fan housings, which resembled the almonds atop a Peter Paul Brand (now Hershey's) Almond Joy bar. The M-3 cars, manufactured in 1960 by the Budd Company, were replaced a few years before their expected lifespan because of their lack of air conditioning and generally shaky ride quality. Early in their service lives, some M-3 cars had fareboxes by their center side doors; these were necessary for collecting fares during the hours after midnight, when SEPTA closed cashier's booths at many stations during the era of 24-hour rapid transit service. "Owl" service (12:00 AM-5:00 AM) trains operated on a twenty-minute headway (interval between trains) at that time.
The M-3 cars, designated Class A-49 for Cars #601-646, and Classes A-50, and A-51 for Cars #701, thru 924, by SEPTA's predecessor, the Philadelphia Transportation Company (PTC), were themselves replacements for both the original "Market Street" cars, designated Class A-8 by SEPTA's predecessor, the Philadelphia Transportation Company (PTC), and built by the Pressed Steel Car Co. of Pittsburgh, Pa. (Cars #1-135, 1906-1911), the J.G. Brill Co. of Philadelphia, Pa. (Cars #136-215, 1911-1913), and the second series "Frankford" cars, designated Class A-15 and built by the J.G. Brill Co. (Cars #501-600, 1922). Though six of the "Frankford" cars survived retirement in 1960 as work train cars (Cars #532, 551, 559, 583, 585, and 589), none lasted as work cars until 2000, nor were any reported to have been saved for museums. The M-3 cars totalled a fleet of 270 cars, which replaced the combined carfleet of 315 cars (215 Market Street cars, 100 Frankford cars), the oldest in operation at the time, was 56 years for a Market Street car, and the youngest was 38 years for a Frankford car. No class of subway-elevated car in Philadelphia, has surpassed the lifespan record held by the Market Street cars.
|0.0||69th Street Terminal||A||B||aerial||100, 101, and 102.|
|0.4||Millbourne||A||B||aerial||originally called 66th Street, rebuilt station opened June 16, 2008|
|0.8||A||B||aerial||31, Previous connection, Route 31 trolley||Westernmost elevated station in city and county of Philadelphia. Last of the original 1904-1908-built Market St. elevated stations, to be in service through 2008. Closed for total reconstruction as of June 2008.|
|1.1||60th Street||A||B||aerial||Previous connection, Route 46 trolley||rebuilt station opened June 18, 2007|
|1.5||56th Street||A||B||aerial||31, G||rebuilt station opened February 27, 2006|
|1.9||52nd Street||A||B||aerial||31, 52; Previous connection, Route 70 trolley|
|2.5||46th Street||A||B||aerial||rebuilt station opened April 14, 2008|
|3.2||40th Street||A||B||30, 40, LUCY Gold, LUCY Green; diverted/nighttime routes of Subway-Surface lines||original station at 40th Street was elevated.|
|3.7||34th Street||A||B||31, LUCY Gold, LUCY Green||original station at 36th Street was elevated. Previous connection at 36th St. was Rte. 67 trolley.|
|4.1||30th Street||A||B||9, 30, 31, 44, 121, 124, 125, LUCY Gold, LUCY Green, Amtrak and SEPTA Regional Rail.||Free transfer to Subway-Surface Lines. Original station at 32nd Street was elevated. Previous connections at 32nd St. elevated station were Rtes. 10, 11, 12, 31, 34, and 38 trolleys.|
|5.1||15th Street||A||B||17, 27, 31, 32, 33, 38, 44, 48, 121, C, Regional Rail at Suburban Station.||Free transfer to Subway-Surface Lines and Broad Street Line.|
|5.4||13th Street||A||B||17, 33, 44, 48, 121, 124, 125.||Free transfer to Subway-Surface Lines.|
|5.6||11th Street||A||B||23; Regional Rail at Market East Station, Greyhound, other intercity buses, & New Jersey Transit buses at Philadelphia Greyhound Terminal|
|5.8||8th Street||A||B||47, 61, Broad-Ridge Spur, PATCO Speedline; Previous connection, Route 47 trolley, Route 61 trackless trolley|
|6.0||5th Street||A||B||Previous connection, Route 50 trolley|
|7.1||Spring Garden||A||B||aerial||25, 43||Replaced the Fairmount station when I-95 was built|
|8.9||York–Dauphin||B||aerial||3, 39, 89||split between York northbound and Dauphin southbound. Original name of station was Dauphin-York.|
|10.2||Allegheny||A||B||aerial||3, 60, 89|
|11.3||Erie–Torresdale||A||B||aerial||3, 56 Rtes. 3, and 56 were previously trolley routes.||Originally called Torresdale.|
|11.8||Church||B||aerial||3, 5||Originally called Ruan-Church.|
|12.3||Margaret–Orthodox||A||B||aerial||3, 5, 59, 75, 89, J, K Rtes. 3, 5, 59, and 75, all previously were trolley routes.||Original called Margaret–Orthodox–Arrott.|
|12.9||Frankford Transportation Center||A||B||aerial||3, 5, 8, 14, 19, 20, 24, 25, 26, 50, 58, 66, 67, 73, 84, 88, R||This station replaced Bridge-Pratt (Frankford Terminal)|