A driver whose train collided with another waiting at a busy station had been held responsible for six previous incidents, according to an accident report.
The seventh incident, in which a Greater Anglia train hit an empty "stabled" train at platform six at Norwich station, left eight passengers needing hospital treatment and others being treated at the scene.
The driver either had a lapse of concentration or "a microsleep", concluded the report into the Norwich incident by the Rail Accident Investigation Branch (RAIB).
The Norwich accident happened just after midnight on July 21 last year and involved a service from Great Yarmouth with 35 passengers aboard.
Before that, between June 2010 and July 2012, the driver had been involved in six incidents "for which he had been held responsible by Greater Anglia", said the report.
The incidents included speeding, overrunning a station and stopping short of a station and releasing the doors.
The report said the RAIB had found that the driver "had a previous operational history indicative that he was prone to lapses in concentration, and that this had not been identified by Greater Anglia's competence management system".
The report went on: " Greater Anglia's investigations of the previous incidents that the driver had been involved in had not raised any concerns about the driver's ability to maintain concentration.
"This was because the driver manager who carried out the investigation had not been trained to consider that incidents, seemingly different in nature, could be linked by underlying behavioural issues. Opportunities to formally review the driver's operational history were missed and this was also not identified by the internal audits conducted by Greater Anglia."
The RAIB said the train at Norwich was going at 8mph when it hit the stationary train and that the concentration lapse or the microsleep would have occurred in the last 20 seconds of the driver's approach to the station.
The report said the RAIB "identified some factors which may explain the driver's possible lapse in concentration (ie the noise made by the passengers immediately behind his cab and the various thoughts occupying his attention at the time of the approach)".
The RAIB went on: "Also, the driver was tired through a short-term lack of sleep, and his performance might also have been affected by the prescribed medication that he was taking.
"These could have been other factors leading to a lapse in concentration, or they could have led to the driver having a microsleep."
Four recommendations were made by the RAIB to Greater Anglia "with respect to its competence management system, its accident and incident investigation procedures, its auditing processes and its fatigue management system".
A further recommendation was made to Network Rail, with the support of Greater Anglia, concerning train movements at Norwich.