By Mark Whitaker
BBC News, Bolivia
It seems perverse that one of the main roads out of one of the highest cities on Earth should actually climb as it leaves town.
But climb it does - just short of a lung-sapping five kilometres (three miles) above sea level, where even the internal combustion engine is forced to toil and splutter.
Then it pauses for a while on the snow-flecked crest of the Andes before pitching - like a giant white knuckle ride - into the abyss.
The road from Bolivia's main city, La Paz, to a region known as the Yungas was built by Paraguayan prisoners of war back in the 1930s.
Many of them perished in the effort. Now it is mainly Bolivians who die on the road - in their thousands.
In 1995, the Inter American Development Bank christened it the most dangerous road in the world. And, as you start your descent, and your driver whispers a prayer, you begin to see why.
The bird's eye view is on the left, on the front seat passenger's side, where the Earth itself seems to open up.
A gigantic vertical crack appears. Way below, more than half a mile beneath your passenger window, you can see - cradled between canyon walls - a thin silver thread: the Coroico River rushing to join the Amazon.
Crosses at the roadside mark the locations of fatal accidents.
On the driver's side there is a sheer rock wall rising to the heavens. There is no margin of error. The road itself is barely three metres wide. That is if you can call it a road.
After the initial stretch to the top of the mountain it is just dirt track. And yet - incredibly - it is a major route for trucks and buses.
Drivers stop to pour libations of beer into the earth - to beseech the goddess Pachamama for safe passage.
Then, chewing coca leaves to keep themselves awake, they are off at break-neck speeds in vehicles which should not be on any road, let alone this one.
Perched on hairpin bends over dizzying precipices, crosses and stone cairns mark the places where travellers' prayers went unheeded. Where, for someone - the road ended.
But even these stark warnings are all too often ignored. As first one - and then a second impatient motorist - overtook our car on the ravine side of the road, my own driver - who hardly ever spoke a word and only then in his native Aymara - intoned loudly, eerily and in perfect English..."You will die."
It is not a rash prediction to make.
Every year it is estimated 200 to 300 people die on a stretch of road less than 50 miles long. In one year alone, 25 vehicles plunged off the road and into the ravine. That is one every two weeks.
Extreme weather conditions make driving more hazardous.
It is the end of the dry season in Bolivia. Soon the rains will come - cascading down the walls of the chasm. Huge
waterfalls will drench the road - turning its surface to slime.
Then will come those heart-stopping moments when wheels skid and brakes fail to grip. There are stories told of truckers too tired - or too afraid - to continue, who pull over for the night, hoping to see out an Andean storm. But they have parked too close to the edge. And as they sleep in their cabs, the road is washed away around them.
This is not the place to drop off.
But for now the road is a ribbon of dust. Every vehicle passing along it churns up a sandstorm in its wake.
Choking, blinding clouds obscure the way ahead. Around one hairpin, a cloud of debris was beginning to clear.
As it did, I could see people milling around in the road. Passengers from one of the overloaded and decrepit buses which run the gauntlet of this road.
It seemed at first that they had got off to stretch their legs, while their driver argued with another vehicle coming in the other direction about who should give way. (Reversing is not something you undertake lightly on a cliff edge.)
It transpired instead though, that the bus driver was dying. Blinded by the dust, he had run into the back of a truck. The bus's steering column had gone through him - severing his legs.
There was nothing anyone could do. Mobile phones do not work here. In any case, who would you call? There are no emergency services.
And no way of getting help through, even if any were to be found. The bus driver bled to death.
We edged past the crumpled bus, and headed on.
Further down the road we passed a spot where a set of fresh tyre tracks headed out into the void. They told their own story.
High in the Andes, they are building a new road. A by-pass, to replace the old one. But this is Bolivia, and already it has been 20 years in the making.
Who knows when it will be complete? Until it is, people will have to continue offering up their prayers, and taking their lives in their hands on the most dangerous road in the world.
From Our Own Correspondent was broadcast on Saturday 11 November, 2006 at 11.30 GMT on BBC Radio 4. Please check the programme schedules for World Service transmission times.