A frog war occurs when a railroad company attempts to cross the tracks of another, and this results in hostilities, with the courts usually getting involved. It is named after the frog, the piece of track that allows the two tracks to cross, and is usually part of a railroad switch.

Sometimes the first railroad was built specifically to delay the completion of the second.

List of frog wars

The first railroad built is listed first.

• December 2, 1870 to January 9, 1871: Erie Railroad vs. Delaware, Lackawanna and Western Railroad's Boonton Branch at the west end of the Erie's tunnel in Jersey City, New Jersey
• January 6 and January 7, 1876: Mercer and Somerset Railway (Pennsylvania Railroad) vs. Delaware and Bound Brook Railroad (Reading Railroad) in Hopewell, New Jersey
• March 1886: Erie Railroad vs. New Jersey Junction Railroad (New York Central Railroad) at King's Bluff near Weehawken, New Jersey
• September 1891: Central Railroad of New Jersey vs. Jersey City, Newark and Western Railway (Lehigh Valley Railroad) in southern Jersey City, New Jersey
• March 1894: Cape May and Millville Railroad (Pennsylvania Railroad) vs. Tuckahoe and Cape May Railroad (Reading Railroad) at Woodbine Junction, New Jersey
• 1897: Pennsylvania Railroad vs. New Jersey Junction Connecting Railway (Lehigh Valley Railroad) in Jersey City, New Jersey