Travel control method and travel control apparatus

1. A travel control method executed by a travel control apparatus, the travel control apparatus comprising:

a first detector configured to detect an obstacle around a subject vehicle traveling in a first lane; and

a second detector configured to detect a second lane adjacent to the first lane,

the travel control apparatus being configured to:

set a first range at a target position for lane change in the second lane, the first range having a size equal to or larger than a size which the subject vehicle occupies on a road surface;

detect a range in the second lane as a second range, the range in the second lane being located at a side of the subject vehicle, the obstacle being absent in the range in the second lane; and

permit the subject vehicle to change lanes when the second range includes the first range,

the travel control method comprising:

a first step of determining a travel scene of the subject vehicle on a basis of a travel state of the subject vehicle;

a second step of acquiring a necessity level of lane change that is predetermined in the travel scene; and

a third step of performing correction to reduce the first range or increase the second range when the necessity level is a first determination value or more as compared with when the necessity level is less the first determination value.

2. The travel control method according to claim 1 , wherein the third step includes performing correction to increase the first range or reduce the second range when the necessity level is less than a second determination value as compared with when the necessity level is the second determination value or more, wherein the second determination value is smaller than the first determination value.

3. The travel control method according to claim 1 , wherein

the travel scene includes at least one of a scene of heading to a destination, a scene in which the first lane is obstructed ahead, a scene in which an emergency vehicle is approaching, a scene in which a parking vehicle exists ahead in the first lane, and a scene of overtaking a preceding vehicle traveling ahead in the first lane, and

the necessity level is set for each travel scene.

4. The travel control method according to claim 1 comprising:

estimating the second range after a predetermined time; and

permitting the subject vehicle to change lanes when the second range after the predetermined time includes the first range.

5. A travel control apparatus comprising:

a first detector configured to detect an obstacle around a subject vehicle traveling in a first lane;

a second detector configured to detect a second lane adjacent to the first lane; and

a controller configured to:

set a first range at a target position for lane change in the second lane, the first range having a size equal to or larger than a size which the subject vehicle occupies on a road surface;

detect a range in the second lane as a second range, the range in the second lane being located at a side of the subject vehicle, the obstacle being absent in the range in the second lane; and

permit the subject vehicle to change lanes when the second range includes the first range,

the controller being further configured to:

determine a travel scene of the subject vehicle on a basis of a travel state of the subject vehicle;

acquire a necessity level of lane change that is predetermined in the travel scene; and

perform correction to reduce the first range or increase the second range when the necessity level is a predetermined value or more as compared with when the necessity level is less the predetermined value.