Two train drivers were so tired - or "so fatigued" - that they passed signals at danger, at a junction to the west of Reading Station.
The Rail Accident Investigation Branch said both incidents happened because the drivers had not had enough sleep and, therefore, were unable to properly control the trains.
This was, in part, due to the rest facilities at Acton not being 'fit for purpose', and because the drivers were nearing the end of a long night shift.
The first incident happened at 0822 on 28th March 2015, when a freight train running from Acton to Westbury, operated by DB Schenker Rail (UK), passed a signal at danger at Reading Westbury Line Junction.
A similar incident occurred at 06:11 hrs on 3 November 2015 when another freight train, forming the same service from Acton to Westbury, and operated by the same company, passed a signal at danger at Ruscombe Junction, about seven miles east of Reading.
RAIB began an investigation into both of these incidents following the latter event at Ruscombe Junction, owing to the similarities between them.
As a result of this investigation, RAIB has made three recommendations covering shift planning at Westbury depot, managing people who may be suffering from tiredness, or identifying them, and look at the risk of fatigue.
RAIB has also identified two learning points concerning the importance of preparing for duty and reporting fatigue, and the role of napping (and facilities for such) within a fatigue risk management system.
Simon French, Chief Inspector of Rail Accidents said: "An admission of tiredness should not be seen as a weakness - it may be the unavoidable consequence of the work and home demands placed on a driver.
"This report has highlighted the ‘real-world’ experience of freight train drivers. By necessity, many freight trains must operate at night and many drivers are required to work long and irregular shifts, often during night hours.
"This means that drivers must accommodate their sleep, home responsibilities, social life and commuting in the hours that remain – and this can be a challenge. For this reason I urge freight operating companies, their employees and trade unions to work together to find practical ways of reducing fatigue at work."