Snow-covered alpine hairpin road, light trails

An alpine hairpin

Like this headlight-streaked stretch, most mountain roads are arranged in switchbacks, zigzagging back and forth upslope rather than leading straight to the summit. The snaking shape has two advantages: First, it keeps grades shallow enough for a typical car to climb, and second, a straight-line road would create an easy path for snow melt and other erosive forces, leading to flooding and landslides. Of course, while they're clearly the safest approach to road design on steep surfaces, switchback routes inevitably involve a little white-knuckling while navigating hairpin turns like this doozy in the Italian Alps.