The Effects of Topography on Route Selection

The physical attributes of space, such as the topography, obviously influence the route selection process. Consequently, a route between two locations (1 and 3, but also using the intermediate location 2) may use a path that is not necessarily the most direct. The detour index (direct distance divided by the transport distance) illustrates the importance of physical constraints on route selection.

Route	Direct Distance (1-2-3)	Transport Distance	Detour Index
a	20 km	20 km	1.0
b	20 km	25 km	0.8
c	20 km	30 km	0.666

Route (a) is shortest in terms of distance, but not necessarily the least expensive in terms of construction costs. Route (b) represents a tentative to reduce costs and this at the expense of a direct path. From a rational viewpoint, route (c) will be the one used to link locations 1 and 3. It offers the best compromise between the lost distance (a higher detour) and the supplementary construction costs imposed by construction over rugged terrain.

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