We are standing on the side of a flyover, looking over the edge, and it is a fearful sight.
Behind us, the traffic is pounding past, slowing slightly to take in the scene of northern Italy’s worst road accident.
And ahead of us is the reason why so many people perished here, just a couple of miles from the tourist streets and beautiful canals of Venice.
A gap – a nothingness where there should be something.
To be precise, there should be two lines of metal guardrails here, installed to stop a vehicle falling off the side in the case of an accident.
But instead, all you can see are remnants of a ghastly accident.
Fragments of toughened glass, the lingering smell of burning, and twisted, broken lengths of metal where the guardrail should be.
Bus ‘violently’ veered
A little further down the hard shoulder, the guardrail is intact – and it is clearly old and corroded.
It’s held in place by regular supports built into the surface; where the crash happened, those supports have either been sliced off, or have simply been ripped out.
What we know is that the bus veered violently to the right. What we don’t know is why.
CCTV footage shows the bus driving along, briefly passing out of sight behind another vehicle, and then appearing in shot as it falls from the side of the road.
But when I looked at the road surface, there was no sign of a skid mark; no indication that the driver had hit the brakes to try to slow the vehicle.
A piece of paper, taped to a lamppost, declares that the side of the road is now subject to criminal investigation, but the prosecutors remain wholly unsure what happened.
Did the driver, described as experienced and respected, suffer a catastrophic health problem, for instance?
Or was there a mechanical problem with the vehicle?
Just another grubby flyover
How could something have gone so extraordinarily wrong, here on a flyover that looks just like a thousand other grubby flyovers that we’ve all seen?
Standing here, it is a horrible sight, because you can see exactly what happened – the point where the bus careered off the road, smashed through the barriers and plunged around 50 feet to the road below, where it caught fire.
We drive down to that point. There is still an acrid smell in the air, and the road is discoloured.
Smashed glass litters the roadside and, yards from where the bus crashed down, you can see where people have been sleeping rough.
There is a concrete wall on the far side, dividing the road from the train station.
A ‘gruesome’ tale that leaves unanswered questions
The bus brushed against that wall on its way down, before smashing into the road, killing so many.
It is a gruesome tale, and, standing here now, with lorries already passing by regularly, it feels extraordinary that the traffic is already back using the flyover, and the road below it.
This is, after all, officially a crime scene and Venice is dealing with an extraordinary trauma.
A woman passes us by, carrying flowers that she leaves on the side of the road, adding to a small collection.
She is, she says, just an ordinary Venetian who wanted to pay her respects.
“I am sad, upset,” she said, as another lorry pounds past, drowning out her sadness.
Some of the stories are unbearably sad.
A newborn baby killed. A couple from Croatia who had only been married for 20 days – the wife dead, the husband badly injured in hospital.
I meet Michele Di Bari, Venice’s chief of police.
He called the accident “a moment of great disturbance, of great pain and great suffering, because Venice is the city of the world.
“Tourists come here to admire the beauty and experience the serenity of a wonderful and extraordinary place.
“This is a great loss, a great tragedy, an unexpected, sudden event that shakes every human soul.
“When I arrived on the scene, I couldn’t help but be very upset, because there was an apocalyptic scene before my eyes, an enormous tragedy that the community will struggle to come to terms with.”
On the motorway, the traffic keeps moving, but Italy cannot escape the shadow of this crash, the spectre of tourists dying a horrendous death, and all the questions.
The country will fill in the gap next to the motorway, replace the barriers, repair the road.
But the questions will linger – how could this possibly have happened, and how can the nation be sure it won’t happen again?