The Center City Commuter Connection (CCCC), commonly referred to as "the commuter tunnel", is a passenger railroad tunnel in Center City Philadelphia, Pennsylvania. The tunnel was built to connect the stub ends of the two separate regional commuter rail systems, which were originally operated by Pennsylvania Railroad and the Reading Company, two rival rail companies. This connection was the first of its kind in the United States, enabling through-running of commuter trains and eliminating capacity limitations and operational difficulties imposed by stub-end terminal designs. The concept continues to inform advocacy for similar projects in other U.S. cities, such as Boston's proposed North–South Rail Link and through-running at New York's Penn Station.[1]
All of the SEPTA Regional Rail lines except for the Cynwyd Line pass completely through the four-track tunnel, which contains two underground stations, Suburban Station and Jefferson Station, and the above-ground upper-level concourse for the east–west commuter lines serving 30th Street Station. The tunnel was elected the Outstanding Civil Engineering Achievement for 1985 by the American Society of Civil Engineers.[1]
Planning and development
Suburban Station, located at 16th Street and JFK Boulevard, was the underground terminus of the commuter rail lines of the Pennsylvania Railroad (PRR). The Reading Company (RDG) ran trains on an elevated approach above city streets into the Reading Terminal, located at 12th and Market Streets (one block west of where Jefferson Station was built). The connection, the first of its kind in the United States, was built to allow trains to run through Philadelphia's downtown central business district, by uniting the commuter lines of the two rail systems.
The CCCC was initially proposed in 1958 by R. Damon Childs, a junior land planner with the Philadelphia City Planning Commission, as a way to bring more people into Center City—which was losing population and business activity at the time—and would offer improved access from Philadelphia's western suburbs to the struggling department stores on East Market Street.[1] The proposed connection would permit through-running of the Pennsylvania Railroad and the Reading Railroad suburban lines.
There already was a 0.8-mile (1.3km) subway from 16th Street to 20th Street, a portion of the trackage connecting Suburban Station with 30th Street Station to the west. The tunnel project extended four of Suburban Station's eight tracks 1.7 miles (2.7km) eastward. The proposed tunnel addition would pass just north of City Hall and then pass over the Broad Street Subway. The tracks would run under Filbert Street, would then curve to the north after 11th Street, pass under the Ridge Avenue Subway spur line, and run northward under 9th Street, ascending to join the Reading embankment near Spring Garden Street.
Underground replacement for Reading Terminal—originally to be called 11th Street Station—was part of the Market East redevelopment project. At first the idea seemed preposterous because it required excavation under Philadelphia City Hall, one of the most massive buildings in the world, but city planner Edmund Bacon, initially doubtful about the tunnel, incorporated it into the city's 1960 Comprehensive Plan once he grasped the project's viability and usefulness.[1]
Still, the Commuter Rail Tunnel was considered for years to be a dream that would not come to pass. Funding issues, engineering challenges, and resistance from nearby businesses and residents delayed the start of construction for years.[1]
Construction
Groundbreaking for the tunnel project was on June 22, 1978.[2] The project ultimately would hire 46 contractors and 300 subcontractors. It took six years to complete at a cost of $330million (equivalent to $1.6 billion in 2024).[3] Federal funds, through the Federal Transit Administration (then called the Urban Mass Transportation Administration), paid for 80percent of the project, state funds accounted for 16.66percent, and city funds covered the remaining 3.33percent.[4]
The CCCC is a reinforced concrete box tunnel of cut-and-cover construction. Workers would close the affected thoroughfares, dig track trenches anywhere from 30 to 71 feet deep, lay temporary wooden decking across the street, construct the tunnels, and then build a new street surface on top.[4] Its design and construction were very challenging, as the tunnel weaves both above and below pre-existing subway lines.
Engineering challenges
It was necessary to underpin 12 building structures during the cut-and-cover tunnel construction. Multiple concrete filled, hand dug piers were the normal underpinning technique. However, the 14-story City Hall Annex (built in 1926; now the Marriott Courtyard Hotel) needed special treatment, since one track of the tunnel box passes directly under the building's support columns along Filbert Street.[1]
The Masonic Temple, completed in 1873, was one of the greatest challenges for the contractors and engineers. Originally, concrete piers were constructed underneath the rubble foundations to shore up the structure. But the interior walls of the building started to crack. The solution was to build a steel core concrete retaining wall of 95-pound steel tangent piles set in 24-inch diameter slurry-supported drill holes protected against lateral settlement by hydraulic flat jacks installed horizontally against the piles and actuated when tie-backs were removed during the forming of the tunnel wall.[4]
The elevated Reading Terminal Train Shed, a registered National Historic Engineering Landmark, presented special challenges because full train service had to be maintained throughout the construction of the Commuter Tunnel underneath, with extensive underpinning required. The Reading Terminal had no basement, and train service had to continue uninterrupted during construction. Workers had to cut the Reading Terminal's original weight-bearing columns to make room for the new Market East Station. The old terminal's weight was then shifted to temporary reinforced concrete transfer beams and caissons.[4]
Philadelphia has four subway lines that pass through Center City, and three interfered with tunnel construction at several places. The north-south Broad Street Subway was built in 1928, and it was designed to allow a future subway line to pass over it near City Hall. Clearances were barely adequate for the Commuter Tunnel, and a 20-foot wide section of subway roof was demolished and the tunnel was built while subway traffic was maintained on at least two of the four tracks. Just east of the Broad Street Subway, a 400-foot section of underground trolley tunnel was parallel to the Commuter Tunnel, and it needed to be moved 16 feet to the south, without disrupting regular trolley schedules.
The Commuter Tunnel construction did disrupt Chinatown, where the tunnel turns to the north. The city and contractor project engineers worked closely with the residents and business owners to solve ongoing problems, which included business disruption, parking problems, noise, dust, and traffic flow. The Chinatown Station of the Ridge Avenue Subway lay directly in the path of the Commuter Tunnel, and it had to be demolished and rebuilt on top of the new Commuter Tunnel. This point under the new Chinatown Station at Vine Street and 9th Street is the lowest point on the Commuter Tunnel, about 20 feet below sea level.
Bernard Goldentyer was the CCCC Project Manager for the City of Philadelphia, making him responsible for coordinating the efforts over a dozen different contracts totaling over $250million. The key to the project was supporting and underpinning Reading Terminal which is a historic structure and keeping all the utilities, including phone lines, in Center City intact while the project was done. In a nod to Chinatown for tolerating the construction, artisans and masons were brought in from China to create the Chinatown Arch.[5][6]
Noise mitigation
To keep train noise and vibration from disturbing downtown buildings and their occupants, the tracks use continuously-welded rails on specially cushioned concrete ties. Track level insulation and acoustic panels between the four tracks further deaden train noise. The concrete tunnel structure itself is isolated from adjacent structures by a two-inch layer of cork.[1]
Tunnel completion
The Commuter Rail Tunnel actually lengthened the existing five-block subway built by the Pennsylvania Railroad in the late 1920s from Suburban Station towards 30th Street Station. Thus, the entire tunnel is almost 2.5 miles long, right through the heart of Center City. As originally constructed, Suburban Station's eight tracks ended at a concrete wall near 15th Street. The CCCC extended four of the station's tracks—two in each direction—eastward. The tunnel project also included removing two of Suburban Station's original tracks. In their place, the two island platforms serving the CCCC's through-tracks were widened to about double their previous width.[1]
Finally, the grade of the Commuter Tunnel gradually rises as it heads north, and the 4-track tunnel reaches a portal as it comes to the surface, and the roadbed rises onto an embankment, and connects into the existing elevated ex-Reading Company line, on a direct continuous high-speed alignment. This rise is the steepest grade on the SEPTA Regional Rail system: 2.8%.
Opening
On April 28, 1984, a free shuttle service began operating between Suburban Station and Market East Station. Trains on the former PRR lines began providing service through the connection to and from Market East on September 3, 1984. The last train from Reading Terminal departed on November 6, 1984.[1] After allowing for final track connections to be made, trains from the former Reading Railroad began using the tunnel on November 10, 1984. The Center City Commuter Connection, the four-track (two tracks in both directions) standard-gauge rail link between Suburban Station and the new Market East Station, formally opened for business on November 12, 1984.[3] The old approach to Reading Terminal was then abandoned. It is still mostly present, and is now known as the Reading Viaduct, being actively converted to a linear park (Phase 1 opened in 2018).
The new Jefferson Station has two platforms which are 850 feet (260m) long and 35 feet (11m) wide.[7]
Operations
The tunnel created some immediate operating changes. Previously all trains dead-ended at a Center City station. If a train arrived late at Center City, its next outbound trip could often leave minutes simply by selecting a train's layover time at the terminal. If a train was going to arrive at the terminal very late, its next trip could be filled by a relay train and crew on standby at the terminal, making very simple such things as crew assignments and cash remittances. Now if a casualty train meant a late-leaving train, and some crews never spent any time at downtown stations. If trains on one branch fell late, it virtually guaranteed that trains on another branch would be late. On-time performance was suddenly much more important than previously, because a late train could now mean hundreds of people standing around in downtown station platforms.[8]
Approximately 22 trains per hour run per track as of 2014[update].[9]
Impact and legacy
The tunnel enabled passengers to board a train in Trenton (on what was the Pennsylvania Railroad) and end up at Wyndmoor Station (along the Reading line). Moreover, the commuter tunnel linked all three of Center City's regional train stations, effectively enabling developers to build ambitious projects like Liberty Place, and, more recently Cira Centre and Comcast Center.[1] The tunnel's success in creating a unified regional network has served as a case study for contemporary transportation advocates. Proposals to link stub-end terminals, such as the North–South Rail Link in Boston, championed by leaders including U.S. Representative Seth Moulton, and efforts to implement through-running at Penn Station in New York City by groups like ReThinkNYC, the City Club of New York, and the Tri-State Transportation Campaign, often cite the operational benefits first demonstrated by Philadelphia's Center City Commuter Connection.
The tunnel created what remains the largest through-running, truly unified regional rail network in North America.[8]
Recognition
The Philadelphia Center City Commuter Connection was elected the Outstanding Civil Engineering Achievement for 1985 by the American Society of Civil Engineers (ASCE).[1] A plaque to that effect is on the south wall in Jefferson Station's mezzanine between 11th and 12th Streets.
1 2 Nussbaum, Paul (November 12, 1984). "Tunnel test a success, SEPTA says". The Philadelphia Inquirer. pp.1, 6. Retrieved February 12, 2025– via Newspapers.com.
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