detail on that, but i did want to say that much to you today. reporter: investigators say two separate crews were on the same track. a four-man track crew was traveling in this high-rail truck modified to ride the tracks. it was being operated in reverse, traveling backwards from shady grove to rockville on the northbound track. the truck hit two workers in that same track bed who were installing automatic track control devices. steven is the ntsb s investigator in charge. we ll attain all radio recordings between the crews and the operations control center. we will conduct interviews with the personnel. we will follow up on the drug and alcohol testing that s been performed. reporter: the ntsb is looking into communications between metro s operation control center and both work crews to determine why the truck was traveling on the same track where workers were on the ground. now, the ntsb is interviewing the four workers who survived this accident and they have also be
two metro maintenance crews working the tracks between the rockville station and shady grove this morning were a recipe for disaster. the four man crew was riding the rails in reverse, and in a specially designed truck. they struck and killed two veteran metro workers walking the tracks, who play not have even known they were in the hear. are there officials procedures that are supposed to be in place when you do operate that vehicle in the reverse position, and is it unusual to have two sets of workers in the same area, when that device is being used? those are questions that we will be asking during our investigation. reporter: both victims are transit agency veterans. 68-year-old sing oh has been with them since 1998. jeff gerard since 1990. our hearts go out to the families of the individuals who passed today. a very sad day for us all. reporter: now the hard work begins. ntsb investigators will be looking at lighting and track conditions and focusing on commu