In the pressurised late-night cacophony of a hospital's emergency department, split-second decisions have to be made. The arriving casualties, often strapped to boards, are, of course, the first priority. Anyone who survived a bad crash in which others died will undergo a thorough round of scans and tests.
Those who did not survive the snarl of steel and burning debris are brought to a small prefab on the hospital grounds, where a doctor will make the formal declaration that they were dead on arrival.
But where there has been a car crash involving multiple parties and multiple survivors, decisions also have to be made about the victims' relatives who frantically burst through the hospital doors, pleading for answers.
Senior hospital staff will discreetly make every effort to keep these groups of people separated. Some will be left in the ED waiting room, some will be brought to sit in the so-called BID (Brought in Dead) room. When people are involved in life-changing or life-ending road accidents, the first question is 'Why?' And when human beings are at the outer limits of their terror, the urge to claw toward a rationalisation can be very strong.
The nation was not given the salve of reason to lay on its grief at the loss of the Ashling Middleton (19), Chermaine Carroll (20), Niamh Doyle (19) and Gemma Nolan (19) last week. Road death experts appeared on television but could mouth only platitudes, because what was the lesson of this? Nobody could say.
No road safety campaign would have stopped it, no finger wagging from officialdom would have saved them. The driver, Dayna Kearny (20), who was transferred from Naas to Tallaght hospital with serious injuries, was so far away from the horror-ad cliche of the reckless motorist. A catastrophic mechanical failure, a tyre blow-out of Dayna's Volkswagen Polo have been offered as possible explanations by investigating gardai.
But rather than making any sense of it all, this only seemed to underline the enormous loss. They had all piled in together because they were young students, cadging a ride with friends, doing what we all did at that age. There was no pub or dance or any of the usual precursors to deadly road carnage. They had been travelling from an evening of ice-skating to pick up a laptop.
They were young students, still with the Leaving Cert in the rear view mirror, just making their way in the world. We could not for a second blame them. And their innocence prevented us from making sense of any of what happened.
There was the agonising small coincidences and fatal decisions of the lead up to the crash: Niamh Doyle hadn't wanted to go skating because she wasn't able to master it. She might have easily opted to give this journey a miss.
The throngs of school uniform-wearing girls who attended the funerals called to mind that Wilfred Owen line - "the pallor of girls' brow will be their pall". And there was the awful bigger picture of the impact that the girls' deaths would have on their families. Ashling Middleton's mother, Sharon, lost her only daughter in the crash. Seven years ago her husband had also died. Mother and daughter had leant on each other and now we can only imagine the pain she is in.
In the aftermath of a crash, when the physical healing begins, our embattled healthcare system allows for counselling for survivors. Perhaps that will be offered to Przemyslaw Gorkowy, the driver of the van that collided with the car the girls were driving.
"I just keep seeing the accident again and again and again," Gorkowy told The Star. "I am lucky to be alive, I thought I was going to die. I feel so sorry for the girls who died. It is terrible. I cannot stop thinking about the girls."
An emotional Gorkowy said that he would like to meet the families of the deceased girls. He was only slightly hurt, but his friend Mariusz Wawrzos (35) was badly injured and taken to hospital.
Facebook, of course, lit up with tributes to the four girls, but there was also a sinister element to it. Before the girls' families all knew of what had happened to their daughters, there was already speculation about the fate of the four women on social media. It brought to mind the ghoulish filming of the crash in Waterford before Christmas and served as another reminder that, for all the sincerity, social media and the ubiquity of smartphones hasn't made us better people.
The particular mysteries of crash physics confounded a nation. How, on a seemingly open stretch of road, could such a tragedy have occurred? The conditions were cold and windy but the road was apparently not slippery. A tyre blow-out on the car in which the girls were travelling has been posited as the catalyst for the crash, but this seemed such a flimsy scapegoat for the grief felt by all who knew these girls. How could a tragedy of this magnitude have been caused by something as mundane as frayed rubber?
Crash experts say that in many cases, even the most brutal road accidents preserve the positions of the passengers in the car. This was not one of those crashes - the vicious force of torque blew off the roof of the car and, according to Fr Frank McEvoy who administered the last rites, their young bodies were strewn on the road.
And yet, for all of those who knew them, the crash stopped these young women in time. It preserved them forever the way they were, lifelong friends, linked forever in death.