Newkirk spent much of the 1830s leading efforts to raise money for and then build a rail line from Philadelphia south to the cities of Wilmington, Delaware, and Baltimore. Four railroads were chartered by the various states; Newkirk funded and directed the building of one of these, then orchestrated the merger of all four. In 1838, the merged PW&B began direct rail service between the cities, broken only by a ferry across the Susquehanna River. Much of its right-of-way is still in use today by Amtrak's Northeast Corridor.
