Tuesday's Amtrak derailment near Philadelphia that has so far killed eight people and injured more than 200 others could have been avoided with the use of technology known as Positive Train ...

The authority is swapping new cars for far older models on the Q train in preparation for the launch of a modern signal system on the E, F, M and R lines.

It relies on computers and wireless technology — instead of people — to automatically control train movements. But the system upgrade is at risk.