Vehicle control method and vehicle control device

1. A vehicle control method comprising:

detecting, on a planned travel route of a host vehicle, a merging section in which a travel lane in which the host vehicle is traveling merges with another lane;

determining, before starting merging assistance control for assisting the host vehicle to change lanes into the other lane in the merging section, whether or not to execute the merging assistance control;

when a determination is made that the merging assistance control is not to be executed in the merging section, determining whether or not a speed of the host vehicle is higher than a predetermined speed, the predetermined speed being set to be larger than 0 and lower than a speed limit of the travel lane of the host vehicle; and

when the determination is made that the merging assistance control is not to be executed in the merging section and the speed of the host vehicle is determined to be higher than the predetermined speed, controlling the speed of the host vehicle so that the host vehicle passes through a starting point of the merging section after decelerating the host vehicle down to the predetermined speed.

2. The vehicle control method according to claim 1 , wherein the predetermined speed is slower by 10 km/h or more than a lowest speed among the speed limit of the travel lane in which the host vehicle is traveling, a speed limit of the other lane, and a travel speed of a front vehicle traveling in front of the host vehicle.

3. The vehicle control method according to claim 1 , comprising determining a deceleration completion point for finishing decelerating the speed of the host vehicle down to the predetermined speed so that when the host vehicle accelerates at a predetermined acceleration from the deceleration completion point, the speed of the host vehicle can reach a speed limit of the other lane by a time the host vehicle passes through the starting point.

4. The vehicle control method according to claim 3 , wherein the host vehicle has an automatic constant travel speed feature for causing the host vehicle to travel at a set speed, in which a deceleration for decelerating the speed of the host vehicle down to the predetermined speed is set larger than a deceleration for decelerating by the automatic constant travel speed feature when the set speed is lowered.

5. The vehicle control method according to claim 3 , wherein the host vehicle has an automatic constant travel speed feature for causing the host vehicle to travel at a set speed, in which when the speed of the host vehicle is equal to or less than the set speed after completion of manual merging operation by a driver in the merging section, the host vehicle is accelerated up to the set speed.

6. A vehicle control device comprising:

an actuator configured to control a speed of a host vehicle; and

a controller configured to:

detect a merging section in which a travel lane of the host vehicle merges with another lane on a planned travel route of the host vehicle;

determine, before starting merging assistance control for assisting the host vehicle to change lanes into the other lane in the merging section, whether or not to execute the merging assistance control;

when a determination is made that the merging assistance control is not to be executed in the merging section, determine whether or not a speed of the host vehicle is higher than the predetermined speed, the predetermined speed being set to be larger than 0 and lower than a speed limit of the travel lane of the host vehicle; and

when the determination is made that the merging assistance control is not to be executed in the merging section and the speed of the host vehicle is determined to be higher than the predetermined speed, control the actuator so that the host vehicle passes through a starting point of the merging section after decelerating the host vehicle down to the predetermined speed.