1. ### Reshma

777
Why do mountain roads rarely go straight up the slope but wind up gradually?

2. ### Vern

123
The roads follow natural inclines that are not so steep. You will do this same thing naturally when walking up a steep incline, you go up at an angle because the walking is easier in the short term.

3. ### Tide

3,143
Because cars can't go "straight up" and roads that go straight up would tend to crumble to say nothing of how extraordinarily difficult (and expensive) it would be to construct such a road.

4. ### robphy

4,225
Picture an inclined plane wound around the mountain.
A smaller force is required to climb to the top, although one must travel a longer distance.

5. ### Moonbear

12,266
Staff Emeritus
About the steepest stretch of road I've ever been on was a 15% incline, and that was truly pushing the cars to maintain speed (a lot of other cars couldn't maintain speed; any steeper and I'd have probably hit maximum RPMs I could hit without blowing the engine). One also has to consider that mountains are also more prone to freezing conditions, and a very steep incline will become completely impassable in inclement weather. The engineers could probably answer this better.

6. ### Tide

3,143
Moonbear,

I think you did a fine job of answering the question!

7. ### HallsofIvy

40,308
Staff Emeritus
I once made the mistake of stopping on a steep mountain road. I couldn't get the car moving forward: it just couldn't get up the initial acceleration! I wound up backing down to the bottom to get a running start.

8. ### DaveC426913

16,081
I once took a shortcut in a camper van. It went up a very steep incline of loose gravel road. I reached a point where all I was doing was spinning the wheels. I couldn't turn around; any movement at all, including reversing caused me to start slipping. It was all I could do to stay in one spot.

So I rappelled down the slope.

I would let off the brake just enough to start moving, then put the brake on and let it slide a few more yards until I stopped, then do it again until I reached bottom.

It was a while before my father lent me his camper van again...

It was a while longer before my wife would go camping with me again...

9. ### Reshma

777
Thanks for the explanation everyone!

10. ### Chronos

9,873
Don't forget flash floods and avalanches.

11. ### Reshma

777
Can this be explained by,

$$\tan{\theta}=\frac{v^2}{gr}$$

where $$\theta$$ is the angle of inclination, v is the velocity of the body and g is the acceleration due to gravity, r is the radius of curvature.

12. ### Mk

Hmm... Is it rappelled or grappelled? Grappelled is going up, and rappelled down? Hmm, turns out rappelled is going down, but what is grappelled? Maybe grappelled is both ways.