WASHINGTON ( CNN ) -- A Boston trolley operator killed in a crash last year likely had a sleep disorder and fell into a `` micro-sleep '' shortly before the collision , the National Transportation Safety Board ruled Tuesday . Since last year 's trolley crash in Boston , Massachusetts , there has been another incident on the same line . The safety board , completing a 14-month investigation , faulted operator Ter'rese Edmonds for ignoring a red signal along the tracks but directed harsh criticism at the Massachusetts Bay Transportation Authority which operates the train system . The transit authority failed to screen operators for sleep disorders while enforcing a work schedule that could prevent train operators from getting enough sleep , the NTSB said . The NTSB 's conclusion that Edmonds fell asleep is partly conjecture , the board acknowledged . Edmonds , a part-time trolley operator , had an opportunity for adequate sleep the day of the wreck , although investigators were not able to determine her sleep history . In addition , Edmonds had been given a break earlier in the day , had not complained to co-workers about fatigue and was found to be free of drugs and alcohol . `` We can not say for certain that she did have it ( sleep apnea ) , '' board member Dr. Mitch Garber said . But the NTSB concluded there was a `` high likelihood '' that Edmonds had an undiagnosed sleep disorder , largely because she was obese and because tests showed she had taken doxylamine , an ingredient commonly found in sleep aids , suggesting she had trouble sleeping during at least one of the nights leading up to the accident . In addition , there is a lack of other evidence to explain why Edmonds failed to slow or stop the train , the board concluded . Tests showed that the stopped train could be seen at a distance of 764 feet , and that `` there were multiple opportunities to slow and stop this ( advancing ) train , '' NTSB investigator Wayne Workman said . `` There was not any evidence that brakes were applied . '' Edmonds ' westbound train was traveling at 38 mph when it struck the other train , which was traveling at 3 mph in the same direction . An estimated 185 to 200 passengers were on the two trains during the collision in the Boston , Massachusetts , suburb of Newton . Damage was estimated at $ 8.6 million . The board also noted that the MBTA had not installed systems on its Green Line to prevent two trains from occupying the same stretch of track , the NTSB said . The systems , known as `` positive train control '' systems , would have prevented the accident , the safety board said . One year after the fatal accident , more than 50 people were injured in another accident on the same line . The Boston accident highlights two issues that have risen to the top of the NTSB 's concerns in recent years , positive train control and operator fatigue . The safety board says positive train control issues were involved in two other light rail incidents this year , a May 8 wreck on the same MBTA Green Line and a June 22 wreck which killed nine on Washington , D.C. 's Metro system . `` If technology exists ... on the other ( MBTA ) lines , why would the Green Line not have everything possible ... to prevent accidents from happening , '' NTSB Chairman Mark Rosenker asked . `` I do n't understand that as an operator ; I just do n't . '' The Metro system had a form of positive train separation , but investigators are exploring whether that crash resulted from a circuit malfunction . The safety board said fatigue issues affect all forms of transportation . It noted that two pilots fell asleep during a flight over Hawaii and that sleep issues played a role in a Cosco Busan ship incident in San Francisco , California , and a fatal bus crash in Mexican Hat , Utah . Rosenker said details that surfaced in the Boston trolley crash will guide the NTSB in the future . `` Now it is up to us , because we now are the advocates for these changes , '' Rosenker said . Recommendations resulting from the Boston crash `` raise the bar of safety not only in this system , but across the United States . ''
Obesity , evidence that operator was wearing sleep aid led to investigation . Transportation board criticized for failing to screen for sleep aids . It also criticized lack of systems to prevent trains from using same stretch of track .