Travel assistance method and travel assistance device

A travel assistance device comprising:

• a sensor configured to detect a surrounding environment of a host vehicle, wherein the travel assistance device is configured to:
• determine a travel route and vehicle speed of the host vehicle based on information on the surrounding environment detected by the sensor;
• execute a lane change of the host vehicle using the determined travel route and vehicle speed;
• detect an oncoming vehicle traveling in an opposite lane opposite to a lane in which the host vehicle travels when the host vehicle starts the lane change;
• determine a crossing point between a virtual advancing route of the host vehicle and a linear advancing route in which the oncoming vehicle advances linearly, the virtual advancing route differing from the determined travel route and being a virtual extension of an advancing route of the host vehicle in an advancing direction thereof, the advancing route being based on the determined travel route during a period from start to end of the lane change;
• execute a lane change using the determined travel route and the vehicle speed in a case where a time difference between a first predicted time when it is assumed that the host vehicle reaches the crossing point and a second predicted time until the oncoming vehicle reaches the crossing point is outside a predetermined range;
• and
• when the time difference is within the predetermined range, execute the lane change by changing at least one of the determined travel route or the vehicle speed such that the time difference is outside the predetermined range.

A travel assistance method for performing a turning of a host vehicle using a determined route and vehicle speed, the travel assistance method comprising:

• detecting an oncoming vehicle traveling in an opposite lane opposite to a travel lane when the host vehicle turns and enters the travel lane from a side road;
• determining a crossing point between a virtual advancing route of the host vehicle and a linear advancing route in which the oncoming vehicle advances linearly, the virtual advancing route differing from the determined route and being a virtual extension of an advancing route of the host vehicle in an advancing direction thereof, the advancing route being based on the determined route at a start of the turning;
• executing the turning using the determined route and the vehicle speed in a case where a time difference between a first predicted time when it is assumed that the host vehicle reaches the crossing point and a second predicted time until the oncoming vehicle reaches the crossing point is outside a predetermined range;
• and
• when the time difference is within the predetermined range, executing the turning by changing at least one of the determined route or the vehicle speed such that the time difference is outside the predetermined range.