Bolivia – the world’s most dangerous road.

I was abroad last week when BBC’s Top Gear did its Bolivia Special. They drove three second-hand 4WDs, first hacking their way through the rainforest, then up the steep eastern side of the Andes to La Paz. Then they crossed the altiplano towards the Chilean border, before dropping down past snowcapped high altitude volcanoes to the Atacama desert and the Pacific Ocean. Great television - especially for someone who knows the area.

The so-called World’s Most Dangerous Road is the bit where the all-weather road climbs out of the sweltering forest to the foothills of the Andes, and continues up and up through the fertile Yungas – coffee, fruit groves, flowers – to the high pass at La Cumbre, 4675 metres (15330ft) above sea level.

The “Most Dangerous” label came originally from the Inter-American Development Bank in 1995 – and we know now that American bankers aren’t averse to taking a few risks. Now it’s the USP for anyone selling trips down this way. Or making TV programmes.

In those good old 1995 days, the only road (built by prisoners of war in the 1930s) was an all-weather gravel affair (single track with passing places) which clung to the mountainside with vertical drops on left or right. Traffic usually passed even if there wasn’t a passing place. Occasionally (regularly is a better word) there’s a little shrine with blanched plastic flowers, or a cluster of small rusting crosses, where a wheel must have veered just that bit too far off track. El Camino de la Muerte - Death Road.

In 2006, a new wider road was opened, which follows a different route, albeit mostly just a few hundred metres away on the other side of the valley. It’s a properly metalled and asphalted two-lane surface, with bridges, viaducts and tunnels instead of corrugated iron conduits and dodgy rock overhangs. Some of the time you can still see the old road, which is still open, but with much less traffic.

I’ve been along both these roads, both up and down – down on a mountain bike, up in an MPV people-carrier. Both old and new roads are mountain roads, and as you might expect when you climb some 12000 feet in 40 miles, there are bends, and plenty of them. For the most part, the new road sweeps up the right-hand side of the valley, with steep drops on the left. The old road hugs the mountainside on the left of the valley, with sheer and apparently fathomless drops on your right.

Knowing this, and watching Top Gear on iPlayer, set me musing.

On the old road, if you’re ascending you’d be right next to the edge of the abyss. But most of the time the Top Gear lads weren’t. They were hugging the mountainside. From this, it’s evident that they were driving on the left, and it’s certainly true that the convention on the old road is that those coming up have right of way, and those going down give way. Descenders are also on the left, next to the drop...you can lean out of the window and see how close your wheels are to eternity.

I suspect that they also must have actually filmed some of it going down.

The old trick of cinema. Set the scene for going up, and the willing suspension of disbelief does the rest. There’s certainly one scene where Jeremy Clarkson squeezes his Range Rover past on the precipice side, road crumbling away beneath his wheels – great TV, and clearly set up, because they had a long-distance camera filming it.

The convention makes sense. Generally, you descend faster than you climb. If you’re on the outside, and closest to your maker, you’ll naturally slow down if you’re passing someone coming in the other direction.

There are several companies in La Paz which offer downhill mountain-bike full-day excursions – of which Gravity Assisted Mountain Biking is by far the best and most safety-conscious. The latter is important. Whichever side of the valley or the road you’re on, you’re at the bottom of the pecking-order on a bike.

Caption for photograph: The sign at the beginning of Death Road reads " TAKE CARE Mr Driver Drive on the left as far as Caranavi Give way to traffic travelling towards La Paz Keep headlights on day and night Sound your horn before each bend"