US Patent 7194355 Navigation system

When a vehicle performs route calculation at a current position, the number of lanes at the current position is found. A predetermined correspondence between the numbers of lanes and straight prioritized distances is used to find a straight prioritized distance at the current position corresponding to the number of lanes. A route to a destination from the current position is calculated so as to include, in the route, a road to be followed for the straight prioritized distance from the current position. When there are many lanes, the straight prioritized distance is set to be long. Accordingly, it is possible to avoid calculating a route that causes a guide to sudden right or left turn. When there are a few lanes, the straight prioritized distance is set to be short. Accordingly, it is possible to avoid calculating a roundabout route to the destination.