injured hundreds. there is a local radio call from a local commuter train about its windshield being shattered. transit 1, let those personnel know that that train was shot at so use caution. the engineer for that train also of interest to federal investigators. the lead investigator also stressing the need for the safety technology known as positive train control which they say would have prevented the crash. positive train control automatically stops a speeding train and despite the vast rail system, has only been fully implemented for passenger trains in a handful of places though it is mandated for them nationwide by the end of this year. we have seen countless accidents over the years that is could have been prevented had positive train control been implemented. phillip mena, abc news new york. that positive control system they were talking about is now fully operational along the northbound tracks reopening in philadelphia this morning. so engineers will be alerted to s