switch·back 
(swĭchbăk′)
(swĭchbăk′)n.
1.
a. A sharp bend in a road or trail on a steep incline.
b. A point on a mountain railway where trains reverse direction to continue obliquely up or down a slope without turning.
c. A road, trail, or railway that has such bends or points in it.
d. A section of such a road, trail, or railroad, extending in a nearly opposite direction to the section coming before or after it.
2. Chiefly British A roller coaster.
intr.v. switch·backed, switch·back·ing, switch·backs
To proceed in sharp turns in alternating directions on a steep incline: the trail switchbacked up the mountain; the hikers switchbacked up the hill.
switchback