The MBTA says that fully restoring the signaling equipment destroyed in the June 11 derailment at JFK/UMass will likely take until at least Labor Day, so that means riders will continue to need to allow extra time for their commutes.

But it could have been worse, the T says: "Because of the age of the system and the extent of the damage, initial restoration of the signal system was projected to take approximately one year."

Meanwhile, the T says it still does not know exactly why the derailment happened, although it has ruled out foul play, operator error and track problems:

After disassembling the car that derailed, MBTA personnel are in the process of determining potential causes of its failure through rigorous evaluations of the car’s components. Out of an abundance of caution, the MBTA conducted a rigorous inspection of all related components of all vehicles of the same type involved in the derailment. As of today, Friday, June 21, all vehicles of the same type involved in the derailment have been inspected.

The T says that until the signal systems are fully repaired, it has to have 50 workers manually switching trains through JFK/UMass, where the Braintree and Ashmont tracks diverge and come together.