In the navigation system, it is very important not
only to find the shortest path but also a detour, in
case of a traffic jam for example. This paper surveys
algorithms for the shortest path problem and the
k shortest path problem at first, extends the latter
algorithm for the 2-terminal k shortest paths problem,
using AI search techniques such as the bidirec-
tional A 3 algorithm, then defines `detour' precisely,
and proposes algorithms for finding a realistic detour
based on these algorithms. The efficiency and property
of the algorithms are examined through experiments on an
actual road network.