mountain roads rarely go straight up the slope but wind up gradually explain why
It’s due to physics. When a vehicle climbs a incline it is acting against two forces, the force of friction acting against the tires, and the force of gravity acting in part (in relation to the angle of incline) against the car. As an incline increases the force placed against the car due to gravity increases. To counteract against this the car must accelerate. However, at a certain point the car will not be able to overcome the force of gravity and will either stop or be forced backwards. As well, the same problem occurs only opposite when you go down the hill. In that the velocity of the car is amplified by the force of gravity, and there is only so much tolerance brakes can take. At a certain point the car will not be able to stop.