A curve of a road such as an expressway or a main highway includes an inlet straight portion that is an inlet of the curve, an inlet clothoid portion continuous to the inlet straight portion, an arc portion continuous to the inlet clothoid portion, an outlet clothoid portion continuous to the arc portion, and an outlet straight portion continuous to the outlet clothoid portion. Such a configuration of the road enables a vehicle to travel smoothly at high speed so that side-slip of the vehicle can be reduced and uncomfort of a passenger can be reduced.
On the other hand, an intersection in an urban distinct, for example, includes only an inlet straight portion, an arc portion continuous to the inlet straight portion, and an outlet straight portion continuous to the arc portion and does not include an inlet clothoid portion and an outlet clothoid portion in some cases.
FIG. 23 is a plan view illustrating an example of an intersection. This intersection 200 is a crossroad where four roads meet. In a case where a vehicle 300 enters the intersection 200 along an arrow 201 from the left in the drawing and travels out of the intersection 200 along an arrow 202 upward in the drawing, the vehicle 300 passes through an inlet straight portion 203, an arc portion 204 continuous to the inlet straight portion 203, and an outlet straight portion 205 continuous to the arc portion 204.
As a relevant technique, Patent Document 1 listed below describes a driving assistance system that creates a virtual digital travel track using a line, an arc, a clothoid curve, and so forth based on a road parameter and positional information on a vehicle.
Patent Document 2 listed below describes a road map creation device that detects coordinates of a current location of a mobile object at each predetermined time and, based on a group of detected coordinates, creates a map of roads constituted by straight portions, non-straight portions continuous to the straight portions, and straight portions continuous to the non-straight portions.