New Jersey Transit train service could be halted in New Jersey if a deadline for a safety program isn't met.

There is a Dec. 31 deadline for railroads to install Positive Train Control systems, or PTC, which automatically stop a train that speeds or disobeys a signal.

NJ Transit says it doesn't expect full PTC implementation until 2018.

Sen. Cory Booker joined six other Democratic senators Thursday asking for a three-year extension. 

Railroads and individual employees operating trains on systems without PTC after Dec. 31 could face fines, and NJ Transit officials have said in published reports that it's unclear whether the railroad would be able to operate without it.

Federal safety experts say PTC could have prevented the May 12 derailment of an Amtrak train that killed eight people in Philadelphia.