The Baltimore and Philadelphia Railroad was a railroad line in the United States, built by the Baltimore and Ohio Railroad (B&O) from Philadelphia, Pennsylvania, to the Maryland-Delaware state line, where it connected with the B&O's Philadelphia Branch to reach Baltimore, Maryland. It was built in the 1880s after the B&O lost access to its previous route to Philadelphia, the Philadelphia, Wilmington and Baltimore Railroad (PW&B). The cost of building the new route, especially the Howard Street Tunnel on the connecting Baltimore Belt Line, led to the B&O's first bankruptcy. Today, the line is used by CSX Transportation for freight trains.
History
19th century
In 1838, the B&O began service from Baltimore to Philadelphia using the new PW&B line. Connecting trackage in Baltimore ran from the B&O's Mount Clare terminal east along Pratt Street and East Falls Avenue to the PW&B's President Street Station. From there the PW&B ran east on Fleet Street and Boston Street before leaving onto its own right-of-way.
In 1881, the B&O attempted to gain control of the PW&B, but lost the stock battle to the Pennsylvania Railroad, which informed the B&O that it would lose access to the PW&B line in 1884. This forced the B&O to build a new route to Philadelphia. It acquired the Delaware Western Railroad, which had a charter but no track, merged it into the Baltimore & Philadelphia in 1883, and began construction. While the line in Delaware and Pennsylvania was operated by the Baltimore and Philadelphia, the line in Maryland was operated directly by the B&O as its Philadelphia Branch.
Except at its two ends, the line was built within a few miles to the northwest of the PW&B. At the Baltimore end, the line ended in the Canton neighborhood, with a car ferry across the Patapsco River to Locust Point. At the Philadelphia end, the new line crossed the PW&B and its old alignment (part of the Philadelphia and Reading Railway's branch to Chester, Pennsylvania, and crossed to the east side of the Schuylkill River on the new B&O Railroad Bridge, just south of the Grays Ferry Bridge. A branch split there towards the Delaware River, while the main line continued north along the Schuylkill, with a station downtown, and then passed through the Art Museum Tunnel to Park Junction with the Philadelphia and Reading Railway's main line; this tunnel, the last part of the line to be finished, opened on December 15, 1886.
thumb|The [[CSX Susquehanna River Bridge is the second bridge at this crossing, a steel truss double track design built between 1907 and 1910 near Perryville, Maryland. It replaced a single-track iron and steel bridge built in 1886 during the original construction of the line.