On March 15, 1837, a supplement to the C&A's charter was passed, allowing the branch to New Brunswick connecting with the New Jersey Rail Road to branch off of the C&A at Bordentown rather than Spotswood, to pass through Trenton for a connection with the Trenton Delaware Bridge and the Philadelphia & Trenton Railroad. Portions could be built next to the Delaware and Raritan Canal or along the New Brunswick and Trenton Turnpike. Construction on the branch began in September 1837 between Bordentown and Trenton, where it was built on the east bank of the D&R Canal. The initial branch opened April 4, 1838. Construction on the extension to New Brunswick began June of that year, opening January 1, 1839. The branch continued northeast from Trenton on the east bank of the canal, splitting at Kingston and running cross-country to Millstone Junction, southwest of New Brunswick. That same day, the NJRR was completed from New Brunswick to Millstone Junction. Despite forming one third of the route, the NJRR only got one sixth of the earnings from the joint operation, which ran between Philadelphia and New York City in 5.5 hours. Further connections and realignments: 1839–1867 By 1839, a connection opened between the Philadelphia & Trenton Railroad and the C&A's Trenton Branch, including a bridge over the Delaware and Raritan (D&R) Canal in Trenton. This allowed for through Philadelphia–Jersey City operation, but most traffic continued to run via Camden due to the distance between the P&T's Kensington terminal and central Philadelphia. On May 31, 1854, the C&A decided to realign and straighten the Trenton Branch between Trenton and Deans Pond (near Monmouth Junction) due to bad soil conditions on the bank of the D&R Canal. A plank road, later upgraded to a railroad branch, would be built to connect to Princeton, which the new alignment would bypass. A tunnel under the canal in Trenton was completed in March 1860, for the connection between the P&T Railroad and the new alignment. Construction on the new line began October 1862; the Clinton Street Station on the new line at Trenton opened April 20, 1863, replacing the old State Street Station. The first train ran through the new tunnel on October 5, 1863, and the new line (along what is now the Northeast Corridor) opened November 23, cutting New York City–Trenton time to 2.5 hours. The second track on the new line opened September