Railroad crossing safety on the former Camden and Amboy Railroad line evolved from simple wooden or cast iron warnings in the 1830s to electrically activated signals by the 20th century. The Camden and Amboy Railroad began operating on these tracks in 1835 and after 1871 became part of the Pennsylvania Railroad. From the 1830s until the early 1900s, roadway crossings often relied on signs reading Stop Look and Listen or Look Out for the Locomotive, while only some busy crossings had flagmen, bells, gates, or manually controlled signals. After the low voltage track circuit was introduced in 1872, railroads developed many unmanned crossing warning devices between 1890 and 1920, including combinations of flashing lights, ringing bells, and swinging arms. As electrical technology advanced in the mid 20th century, a more standardized signal appeared, with a crossbuck sign, red flashing lights, and a bell, operated by switches and relays linked to the track circuit and backed by storage batteries in concrete battery boxes during power outages. Illuminated No Left Turn and No Right Turn signals, called blankouts, also warned vehicles away from tracks along parallel streets, and the Pennsylvania Railroad used them extensively between Camden and Bordentown. In the 1950s, Pennsylvania Railroad crossing signals with electrically powered groups of 4 or 8 red flashing lights and a bell protected most grade crossings along the former Camden and Amboy right of way. Although modern signals are larger, brighter, and electronically advanced, their purpose remains to protect pedestrians and motorists and to urge caution at the tracks.