A high pass is only a road for part of the year

Gradient is the constraint that shapes the whole road

A road climbing a mountain has to gain height at a rate that vehicles can manage and that water will not immediately destroy, which means it cannot go straight up. The alignment is therefore a compromise between the shortest line and the tolerable slope, and every hairpin is a place where the engineer bought height at the cost of distance.

That is why mountain distances are so misleading. Thirty kilometres of valley road and thirty kilometres of pass road are different afternoons entirely, and average speeds on a serious pass are a fraction of what the same distance implies elsewhere.

Old roads and new roads solve the same problem differently. The older alignment climbs with the terrain in tight turns and stone retaining walls; the modern one drives through the mountain in tunnels and across viaducts. Where both survive, the old road is usually the better journey and the tunnel is the faster one.

Snow closes passes, and the dates are not decorative

Above a certain height, keeping a road open through winter means clearing snow continuously, protecting it from avalanches and accepting that it will sometimes be shut anyway. For many passes that cost is not worth paying for the traffic involved, so the road is simply closed for the winter and reopened when conditions allow.

Opening and closing dates are approximate by nature, because they depend on the snowpack in a given year rather than on the calendar. Authorities publish a target and adjust it, which means a pass that is normally open by a certain month may not be open in the year you are travelling.

Some passes stay nominally open with restrictions instead. Winter tyre or chain requirements, bans on certain vehicles, and closures overnight or during clearance are all common, and they are enforced with fines in many places rather than treated as advice.

The alternatives are usually a tunnel, a train or a long way round

Where a pass matters economically, there is often a tunnel underneath it, and the tunnel takes the freight and most of the through traffic all year. That is good for the pass, which becomes a quieter and more scenic road, and it means the two routes serve different users.

Several mountain regions also run car-carrying trains through base tunnels, where you drive onto a wagon and are hauled through. It is an ordinary piece of transport in the places that have it, it runs frequently, and it removes both the climb and the weather from the journey.

The remaining option is the detour, which on a mountain range can be enormous. This is worth checking before setting out rather than discovering at a closed barrier, because the distance around a range often bears no relation to the distance across it.

Driving a pass is a different skill from driving a motorway

The two things that catch people out are brakes and oncoming vehicles. A long descent on the brakes alone overheats them, which is why engine braking in a low gear is standard practice on mountain descents and why runaway lanes exist on some roads.

Meeting a bus or a lorry on a single-lane section with a drop on one side is the other common surprise. Local convention on who reverses varies, and on some roads it is formalised in law or by signage, with scheduled buses given priority. Watching what local drivers do for the first few kilometres is more useful than any general rule.

Cyclists and motorcyclists are on these roads in numbers in the season, moving at wildly different speeds from each other, and visibility around a hairpin is short by definition. That combination, rather than the height, is what makes mountain roads demanding.

What the pass road is actually for now

Most great pass roads were built for trade and for armies, and the modern tunnel took that traffic away. What is left is a road whose main users are people who chose to be on it, which is a rare thing in road travel and is the reason these routes are worth driving slowly.

The infrastructure at the top reflects the history. A hospice or refuge founded to shelter travellers, a customs post at the border, a war memorial, a weather station, and a cafe that opens only when the road does. Many of these buildings predate the road in its current form by centuries.

It is also worth admitting that the experience has become popular enough to be crowded on famous passes in high summer, with queues at the hairpins and full car parks at the summit. Going early in the day, or choosing a lesser pass over a famous one, restores most of what the crowd removes.