Passenger travel began to flourish in 1902 when the American Railroad Company from New York acquired the system. In 1904, a southern line was constructed between Hormigueros and Yauco. The northern line was expanded towards the west of San Juan to include the towns of Arecibo and Aguadilla. One of the most significant projects of this line was linking the main rail line through Quebradillas and Isabela, requiring the construction of tunnels and tall bridges, including the Guajataca Tunnel completed in 1904. In 1907, the northern line of San Juan was connected to the southern line of Ponce, finally connecting the northern and southern portions of the island.