Updated

New Jersey Transit says it will reduce its train service as it tries to install a federally mandated safety system by a Dec. 31 deadline.

The service changes will go into effect on June 4 and last through early next year.

Last week the Federal Railroad Administration sent a letter expressing concern that NJ Transit, the nation's third-largest transit system, would miss the deadline to install the emergency braking system, called positive train control.

Through the end of 2017, NJ Transit reported it had only 35 of 440 locomotives equipped with the system, and hadn't finished installation on any track segments.

Last month, NJ Transit Executive Director Kevin Corbett said an overnight test of the system on tracks in Morris County had been successful.