When the process proceeds to step S2, it is checked whether the target route is generated in a direction to turn right or left at the intersection. Note that, even when the target route is set in a linear direction, it is determined that the driver intends to turn right or left when the driver turns on the blinker switch before the intersection. At that time, the target route is rerouted in a right turn or left turn direction. In one embodiment, the process in step S2 may serve as a process performed by a “right-left turn determiner”.

Then, when it is determined that the vehicle M turns right or left at the intersection, the process proceeds to step S3. On the other hand, when it is determined that the vehicle M goes straight through the intersection, the routine is terminated.

When the process proceeds to step S3, a correct route Rc and the erroneous route Re are generated in a direction in which the vehicle M in the intersection turns right or left, and the routine ends. In one embodiment, the process in step S3 may serve as a process performed by a “route generator”.

The process in step S3 is executed according to a correct route and erroneous route generation subroutine illustrated in FIG. 3. In this subroutine, first, in step S11, road information ahead of the vehicle M is read. Examples of the road information include the distance from the current position of the vehicle M to the front of the intersection, the size of the intersection, the position information of a coupling end with the intersection in the right turn or left turn direction, road width information, lane number information, and the like.

This road information is acquired from, for example, the high-precision road map information stored in the road map database 13, or the road-to-vehicle communication, or the forward traveling environment information recognized by the camera unit 26. In this case, it is difficult to acquire the road information of the right turn or left turn destination from the forward traveling environment information recognized by the forward traveling environment recognizer 26d of the camera unit 26 from the current vehicle M position. Thus, it is unclear whether the target route to be generated on the road in the direction to turn right or left is correctly set with respect to the actual lane, and there is a possibility to have a large error.

Next, when the process proceeds to step S12, the driving assistance control unit 21 checks whether the road of a right turn or left turn destination includes two lanes or more on each side from the road information acquired in step S11. Then, when the number of lanes on each side is two or more, the routine is terminated. If there are two or more lanes on one side, it is considered that the vehicle M does not enter the opposite lane side even if the deviation amount of the vehicle lateral position with respect to the target route is large.

Next, the process proceeds to step S13, and the driving assistance control unit 21 checks whether there is an opposite lane on the road in the right turn or left turn direction from the road information. Then, when there is no opposite lane, the routine is terminated. On the other hand, when there is an opposite lane, the process proceeds to step S14. When there is no opposite lane, the erroneous route as described later cannot be generated and thus is excluded.

When the process proceeds to step S14, the correct route Rc is generated at the intersection. As indicated by solid lines in FIGS. 6 to 9, the correct route Rc couples, in the intersection, a target route set to a lane before entering the intersection and a target route set to a lane after turning right or left at the intersection.

Therefore, the target route set in the intersection may be used as the correct route Rc. Alternatively, the correct route Rc may be generated with a curvature between two points of end points facing the intersection of a target route set to a lane before turning right or left and a target route set to a lane after turning right or left.

Thereafter, the process proceeds to step S15, and the erroneous route Re is generated. As indicated by broken lines in FIGS. 6 to 9, as the erroneous route Re, the lane width of the opposite lane of the road in the direction to turn right or left is detected from the road information acquired in step S11, and a route is generated at the center thereof. Then, the route set on the opposite lane side and an end point facing the intersection of the target route set in the lane before entering the intersection are coupled with the curvature between two points, a route is generated in the intersection, and the erroneous route Re is generated by coupling the generated routes in the intersection and the opposite lane.

Next, the process proceeds to step S16, and the data of the correct route Rc and the erroneous route Re generated in steps S14 and S15 is stored in the nonvolatile memory, and the routine is terminated.

The data of the correct route Rc and the erroneous route Re is read by the travel assistance control routine at the time of turning right or left illustrated in FIGS. 4A and 4B. Note that the above-described travel route generation routine at the time of turning right or left is executed at every predetermined calculation cycle until immediately before the vehicle M enters the intersection. Thus, the data of the correct route Rc and the data of the erroneous route Re stored in the nonvolatile memory are sequentially updated with the latest data.

Next, the travel assistance control routine at the time of turning right or left illustrated in FIGS. 4A and 4B will be described. In this routine, first, in step S21, the forward traveling environment information of the vehicle M is read. The forward traveling environment information is acquired from the forward traveling environment information recognized by the forward traveling environment recognizer 26d of the camera unit 26. Alternatively, the forward traveling environment information may be acquired with reference to the high-precision road map information stored in the road map database 13 from the relationship between the target route set by the travel route/target route setting calculator 12b of the map locator calculator 12 and the current vehicle position.

Next, the process proceeds to step S22, and based on the forward traveling environment information read in step S21, it is checked whether the vehicle M has entered the intersection. Then, when the vehicle has not yet entered the intersection, the routine is terminated. On the other hand, when the vehicle M has entered the intersection, the process proceeds to step S23. Note that, in the present embodiment, as illustrated in FIGS. 7 and 9, a vehicle position Vp indicates a front end of the vehicle M and the center in the vehicle width direction. Therefore, the track of the vehicle position Vp becomes the vehicle traveling route Vc.

When the process proceeds to step S23, it is checked whether the vehicle M (more precisely, the vehicle position Vp) has passed through the intersection based on the forward traveling environment information read in step S21