Washington — The National Transportation Safety Board Tuesday recommended that Metro-North adopt new safety measures including cameras on trains and more speed restriction signs.

“The images and audio captured by recorders can be invaluable to our investigators,” said NTSB Chairman Deborah Hersman. “Understanding what is happening inside the cab just prior to a crash can provide crucial information about how to prevent future accidents.”

The recommendations came out of an ongoing investigation into a crash in December in the Bronx, one of four open investigations into Metro-North incidents.

The rash of accidents has prompted the NTSB, and a slew of politicians, to question the railroad’s safety.

Sen. Richard Blumenthal, D-Conn., who has been urging Metro-North to put cameras on its trains, said the railroad should immediately install inward- and outward-facing audio and image recorders instead of waiting for Federal Railroad Administration regulations.

On Monday, Metro-North’s new president, Joseph Giuliettti, said that within 100 days the railroad would compile a comprehensive plan to improve safety, on-time performance and customer communications.