Angus and Margaret MacKay, both 81, from Inverness, and Mr MacKay’s brother Donald, 66, from Latheron, Caithness, died in the accident at an open crossing at Halkirk in Caithness in 2009.
The MacKays’ son, Donald, said he believed the crossing was “not fit for purpose”.
Mr Mackay, a data analyst from Inverness, said Network Rail failed to put in safety measures following previous accidents at the crossing.
“From the very start, Network Rail has been inadequate in the assessment of the crossing. It’s not fit for purpose, and maintenance has been lacking in some respects,” he said.
He added that he was still coming to terms with the deaths and had problems with sleeping and attention.
“I thought after the funeral it would take six months to get back to normal, but more than two years down the line I’m still having problems.”
He is pursuing the case with the help of Cameron Fyfe, of law firm Drummond Miller, who said the main allegation was that Network Rail should have erected a barrier at the level crossing.
The second allegation is that the warning lights are difficult to see when the sun is shining.
Mr Fyfe said: “The main allegation is that Network Rail ought to have erected a barrier at this level crossing because there had been so many incidents there. Had there been a barrier, this particular tragedy would not have occurred.
“[Mr Mackay] is suing for the loss of his parents. He is anxious to show that his parents were not to blame and that if a barrier is now erected it could save lives in the future and their deaths will not have been in vain.”
The accident happened on 29 September, 2009, when the 10:38 train from Inverness to Wick travelling at 47.5mph struck the Nissan hatchback on the level crossing, which had road traffic light signals but no barriers.
A Rail Accident Investigation Branch (RAIB) report into the accident concluded that the driver of the car did not react to the road traffic light signals and drove on to the level crossing at the same time as the train arrived. But it said an underlying factor was that Network Rail did not properly understand the risk at Halkirk level crossing because it had not taken the previous accident record into account.
“Had it done so, the level of risk might have justified more costly risk-reduction measures, and risk-reduction measures that had been identified might have been implemented more quickly and before the accident occurred,” it said.
It also said the poor condition of the backboards to the road traffic light signals, reducing the visibility of the lights, could also have increased the likelihood of the car driver failing to notice the lights.
A Network Rail spokesman said: “It would not be appropriate to comment in detail on a potential claim at this stage.”