NEW footage has been released showing the terrifying moment a boy ran in front of a speeding train.

The footage, released by Transport South Australia, was taken from inside the driver's cabin of the train which narrowly missed the youth as he sprinted across tracks at the Mawson Lakes interchange on April 11 this year.

The youth emerged from behind a stationary train into the path of a Gawler-bound express train travelling at 90km/h.

He was clipped by the train, narrowly avoiding serious injury. Services were stopped for two hours while the incident was investigated.

The footage was released as part of National Rail Safety week and includes a voiceover by a train driver describing the trauma of people running in front of trains.

''Quite often we are caught completely unawares by what people are going to do,'' she says.

"We can put the brakes on but I don't think people realise it takes at least 100-200m to stop.

''We can't be sure whether or not we have hit them or not, we can only what to see if they come out from the side ... it's a horrible feeling not knowing.''

The youth in the video was convicted in the Elizabeth Magistrates Court on August 16, on counts of stopping a train and impeding the proper operation of a passenger transport service.

He was ordered to undertake community service and write a letter of apology to the driver of the train.

Acting South Australian Rail Commissioner Peter Doggett said the youth's conviction reflected the serious nature of trespassing incidents and the difference between the youth's minor injuries and death was a matter of millimetres.

''Such incidents cause significant distress not only to witnesses, but to our drivers who have no course of action other than to pull up their train as quickly as possible which can often take hundreds of metres, and hope they don't hit someone,'' he said.

''Near-misses can cause as much stress and trauma to a driver as serious injury or fatal incidents.

''With National Rail Safety Week happening this week, it certainly is a timely reminder of the dangers of both inattention and trespassing.''