The crash happened near the village of Llanbrynmair, in Powys
Mr Evans, from Capel Dewi, Ceredigion, died after the crash and four others were seriously injured.
A further 11 people sustained injuries which required hospital treatment
On Tuesday, the RAIB issued an update on the investigation, adding that an automated system that helps train wheels grip tracks failed.
It said initial analysis indicated the 1J25 service from Shrewsbury to Aberystwyth was travelling between 15mph (24 km/h) and 24mph (39 km/h).
The 1S71service from Machynlleth to Shrewsbury was travelling at about 6mph (10 km/h) in the opposite direction.
The RAIB is continuing to analyse evidence relating to the collision speed, which it said remained an area of ongoing investigation.
David Tudor Evans, 66, was travelling on a westbound train when it crashed in mid-Wales last month
The RAIB said it inspected the automatic sanding system, which automatically sprays sand via hoses when a wheel slide is detected during braking, in a bid to generate more friction.
It said the inspection of the system fitted to train 1J25 showed these hoses on the leading vehicle of the train “were blocked and apparently unable to discharge sand”.
They told PA news agency that Rachel Evans, Mr Evans’s wife, was “pretty much left to her own devices” after the crash.
The force issued a statement on 22 October saying “the deceased’s next of kin have been informed and his family are being supported by specialist officers”.
But a BTP officer actually visited the family on 23 October, PA reported.
BTP Supt Andrew Morgan said: “British Transport Police has apologised directly to the family of the deceased in relation to this statement and would like to apologise publicly for any additional suffering caused at this extremely difficult time.”
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