What makes a road fun?

Every paved road in OpenStreetMap is measured every 10 metres. A road is scored on its best stretch (up to 15 km), so a great pass isn't dragged down by the valley road leading to it. Its bends are the base, and terrain, scenery and hairpins each add a bonus on top (they don't multiply, so a road isn't rewarded just for having a bit of everything):

1. Bends. How tight the road turns at each point: sweeping (radius under 175 m), flowing (100 m), tight (60 m) or hairpin-tight (30 m). Every kilometre in a bend counts, weighted by your taste: towards Sweepers fast, flowing roads rise; towards Hairpins switchback stacks win. Bends through villages count only 30%: nice to look at, not to ride hard.
2. + Terrain. Up to +0.5 for 1,500 m of climb, or up to +0.3 for rolling crests and dips. Kept modest on purpose: a low road that's all bends (like the Tail of the Dragon) is still a great road.
3. + Scenery. Up to +0.5 for high alpine terrain above the treeline, or where the view opens up below the road (balcony roads above lakes and valleys), runs along a steep drop-off, or passes a marked viewpoint.
4. + Hairpins. The signature of a real pass (150° or more of turning within 120 m): +0.5 for 20, and still a bit more for Stelvio-style stacks of 40 or 60. More or less with your taste.

× Good km. Finally, how much of the road is good riding: the kilometres at least half as good as its best stretch, up to 30 km. Meh stretches neither help nor hurt. A 6 km gem counts ×0.63, 15 km ×1, 30 km of greatness ×1.41.

On the map, the hot spots glow orange and ★ marks the single best bit.

Best 5 km (in Sort) ranks roads by their most intense 5 km alone, scored as if the whole road were that good, for when you'd ride a road for one great climb. It only counts numbered roads and named passes that aren't mostly narrow, and skips stretches through villages, so forest tracks and village lanes don't take over. With In view off it ranks the whole Western Alps.

The scale

Fixed, so scores compare anywhere, and your taste reshuffles roads without inflating them. It's calibrated on the world's benchmark roads: Stelvio 95, Grossglockner 81, Transfăgărășan 81, Tail of the Dragon 71. 100 is the ceiling; a road that measures even higher still shows 100.

What it rewards, and what it can't see

It's a measurement, not a verdict. It rewards lots of bends packed close together, hairpins, climbing and open views. Roads that concentrate all of that score very high even if they're not famous: Col de L'Arpettaz near Albertville hits the ceiling with 57 hairpins in 26 km, more bends per kilometre than the Stelvio, although part of it is a narrow lane.

What the data can't see: how wide the road is (it's rarely mapped), surface quality, traffic, waterfalls, glaciers and cliff walls, how famous or atmospheric a road is, and whether it's open today. So a high score means "this will be very twisty", and a tight mountain lane and a wide famous pass can score the same. Read the warnings and the breakdown on each road, and trust your own taste.

Not in the score, but shown as warnings: narrow or single-lane stretches, tolls, tunnels, and seasonal closures. Unpaved, private and farm-only roads are left out entirely.

Road data changes: check closures and conditions before you ride.