The National Transportation Safety Board blamed impairment from drugs and the failure to require automatic braking devices on freight trains for the collision of an Amtrak passenger train and a string of freight locomotives a year ago. The Jan. 4, 1987, crash near Chase, Md., was the worst in Amtrak's history, killing 16 people. The NTSB concluded after a yearlong investigation that the probable cause of the crash was the impairment of Conrail engineer Ricky Gates from marijuana and possibly alcohol. The NTSB said the effects of marijuana use by Gates and brakeman Edward Cromwell caused them not to notice warning signals until it was too late. Gates faces trial on 16 counts of manslaughter in the accident. Cromwell was granted immunity for his grand jury testimony. The safety board also took Amtrak and the Federal Railroad Administration to task for not requiring that all freight trains operating in the Northeast corridor be equipped with backup automatic braking devices. After the accident, the FRA ordered all such trains to have the automatic equipment.