We travelled in convoy with Didier, Eric, Bernard and Aurelien, the municipal road-clearing crew, driving behind them as they started their day’s work. We stopped while they unlocked the wooden gate barring the road, drove through, stopped again while they locked it again behind us.

It was Wednesday 20 April and they had already been working for two weeks.

The Friday before, they had reached the col; now, they were going down the other side, and were stuck in deep powder about a kilometre and a half from the top.

Just below, marooned in the white sweep of unbroken snow was a large stone barracks, a reminder of why the road existed: until 1860, all of these mountains – and Nice – belonged to Italy. Only then, when Napoleon III took control of the County of Nice, was the Bonette road built, to protect Nice and to hitch the area definitively to France.

While Eric and Bernard widened and tidied the work on the south side, Aurelien and Didier’s task was to make progress down towards Jausiers, the first village to the north. First Aurelien, in the fraiseuse à neige – the snowblower – would clear a narrow passage.

Where the snow was more than about 1.5m high, that meant rolling up a snow slope made by Didier, who was driving a gigantic digger, to roll on top of unknown depths of snow and make a first pass. After that, Didier would clean up behind, widening the cut and digging down until the black tarmac emerged from underneath its white coat.

On a good day, in shallow snow, they could advance a kilometer, Aurelien said.

Today, in drifts up to six metres high, they simply couldn’t get going: Aurelien was having difficulty attacking the high wall in front. Finally, after a moment teetering on the edge, the rollers on the front of the snowblower cut into the vertical barrier, and a fine stream of white crystals sprayed high into the blue air, and down the slopes to the left.

We were off.

What’s the game plan once you get going?

“Orient yourself on the snow poles, and aim just above them,” Aurelien said.

And hope for the best, he could have added. There was a constant struggle to keep the snow-cutting equipment level as the truck tipped sideways and threatened to fall down the slope. More than once Didier had to take time out from shoveling huge snow boulders to tow the snowblower backwards, out of the crevice in which it had got stuck. Apart from that, accidents are rare, though in case of disaster all the guys wear avalanche beacons.

Once the road is clear, the black Tarmac heats in the sun, further melting the snow at the edges – making it safer for riders and spectators at the Giro, as well as the other cyclists, motorcyclists and hikers who use the Route de la Bonette as soon as it is opened.

It’s not only important for the Giro: the valleys on either side see a 30% benefit to their economy once they are turned from ‘col de sacs’ into destinations on the tourist route over the highest road in Europe.

And after the first big effort, any new snow – even heavy falls – can quickly and easily be cleared by a regular snowplough.

The only potential problem for the Giro, predicted Aurelien’s boss, Monsieur Fabron, would be a big storm on the day of the stage itself.

By mid afternoon, the newly uncovered road had turned into a slushy stream in the sun, and it was time for the men to stop work. Aurelien left the snowblower at the snow face, headed up to base and drove back down in the snowplough, to refuel his machine.

Then we shook hands and they were gone, leaving us on a deserted, silent road above the locked barrier, free to ride our bikes between huge walls of snow as the sun disappeared behind the peaks.