Selfie taken shortly before three friends tragically died showed they missed heartbreaking detail

A selfie taken moments before three friends tragically lost their lives revealed a heartbreaking detail.

Back in 2011, Utah County sheriff's Sgt Spencer Cannon said Essa Ricker and Kelsea Webster, plus the latter's little sister, Savannah, waved to engineers of the Utah Railway train as they ventured past the Covered Bridge Canyon crossing in the state.

But what the teens didn't know was that a Union Pacific carrier was coming in the opposite direction.

Cannon went on to say the gap between the two trains was roughly three or four feet.

The teens tragically lost their lives (Union Pacific/Essa Ricker/Kelsea Webster/Savannah Webster)

Essa and Kelsea were instantly killed in the tragic accident, while Savannah underwent surgery at a local hospital, but after doctors told her parents she would not recover from severe brain injuries, life support was withdrawn.

Jayna Webster, Savanah and Kelsea's mom, wrote on her blog at the time: "We spoke to the doctors today and they informed us that Savvy's brain injuries were too great.

"Even though they've had done everything possible, Savannah will not be able to recover any further. We will keep her on life support till the end of the day, but it's time to say goodbye, for now, to an angel that walked among us."

Just moments before the tragic accident, Savannah penned on Facebook: "Standing right by a train ahaha this is awesome!!!!"

Big train enthusiasts, the teens posed for a photo completely unaware a fast train was approaching in the other direction.

The selfie taken just seconds before the tragic incident sees headlights from the fast approaching train creating a halo.

The teens tragically did not hear the horn blasting.

John Anderson, a train conductor working at the time, said: "They were in their own little world."

The trio were stuck by a freight train (Getty Stock Photo)

Engineer Michael Anderson tried to get the attention of the three friends by blasting the train's horn, but to no avail.

"We watched in horror as we got closer," John heartbreakingly recalled. "We saw them for about 12 seconds until they disappeared from our sight and the train continued moving forward."

John sprinted to the track after the train came to a stop and found the first girl had no pulse.

He also came to the realization the second teen was no longer alive, so headed over to Savannah.

She was badly hurt, but alive.

"I told her everything would be OK and she relaxed a little," the conductor reassured the teen.

"I hoped she would make it and for some reason I really thought she would."