The Network Rail review also said there were 584 sites on the rail network across Britain which shared some of the same characteristics as at Carmont, where a ScotRail train derailed when it hit rock and gravel washed onto tracks by a drain.
These included 80 locations in Scotland.
No significant issues “requiring emergency intervention” were found, although defects that have “deteriorated and require action sooner than originally planned” were identified at some six sites.
But Network Rail said it was “simply not economically viable to strengthen all sub-standard infrastructure slopes.”
The report also said there was a need for greater use of technology to predict landslips and improve forecasting.
It came as the operation to move the wrecked carriages of the ScotRail train using a crane got underway.
Driver Brett McCullough, 45, conductor Donald Dinnie, 58, and passenger Christopher Stuchbury, 62, died when the 6:38am Aberdeen to Glasgow Queen Street train crashed on 12 August.
The report stated: “Our operating instructions will be revised to clarify train operating principles during extreme weather, where earthworks are at risk of failure.
“An emergency instruction was issued to signallers on 18 August as a reminder of our operational procedures for reporting and managing services during heavy rainfall.”
Investigators have reported the train was travelling at nearly 73mph, close to the 75mph speed limit for that stretch of line, when it derailed.
Drivers operate under instruction from signallers over any changes to speeds.
Transport Salaried Staffs’ Association general secretary Manuel Cortes said he had asked why all trains weren’t cancelled on the day, and why some were allowed to continue and not others.
Kevin Lindsay, Scotland organiser for train drivers’ union Aslef, said: “Why has it taken the loss of three lives for the Tory Government at Westminster to ask for a report of this nature from Network Rail, when those of us who work in the rail industry have known about these problems - and called for action to put them right - for many years?”
Network Rail chief executive Andrew Haines said: “We are increasingly seeing more incidents of severe weather.
“Earthworks and drainage infrastructure – some of which are more than 150 years old – prove to be a real challenge as the country experiences more heavy rainfall and flooding.”
UK Transport Secretary Grant Shapps said: “We will use the findings of this interim report to improve, shape and accelerate our work to build a more robust and resilient rail network so that our railway continues to be one of the safest in the world.”
Mr Shapps has recommended that Constable Liam Mercer, one of the first people on scene following the derailment, is commended for his bravery. He ran towards the train before pulling people from the wreckage.
Separate investigations into the crash are underway by the Department for Transport’s rail accident investigation branch, and British Transport Police and Police Scotland.
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