A workplace culture that valued speed over safety contributed to two Metro train accidents that killed three employees in 2006, the National Transportation Safety Board said Wednesday in a meeting that laid bare the glaring flaws in the transit agency’s safety procedures.

Before a train running 40 mph hit and killed senior rail mechanic Jong Won Lee at the Dupont Circle station in May 2006, Metro had no policy requiring train operators to slow down when they approached work areas, the NTSB investigation found.