an abrupt deceleration controller;

a storage configured to store celestial data indicative of positions of a sun;

one or more processors, and

one or more memories that store instructions for causing the one or more processors to execute the instructions, the instructions comprising:

acquiring, from a camera, information on a traveling environment in front of an own vehicle that travels in a traveling lane being captured by the camera;

determining whether a first preceding vehicle traveling, in the traveling lane, immediately in front of the own vehicle is recognized on a basis of the information on the traveling environment;

acquiring, in response to the first preceding vehicle being recognized, from an illuminance sensor, an intensity of sunlight detected by the illuminance sensor;

determining whether the intensity of sunlight is greater than or equal to a predetermined threshold, wherein the predetermined threshold indicates a lowest intensity of sunlight for the camera to recognize a shadow of the own vehicle;

in response to determining that the intensity of sunlight is greater than or equal to the predetermined threshold, detecting a vehicle shadow of a train of vehicles including a first vehicle shadow of the first preceding vehicle and a front vehicle shadow of a front vehicle traveling in front of the first preceding vehicle on a basis of a difference in brightness from a road surface;

determining whether the front vehicle shadow separating from the first vehicle shadow of the first preceding vehicle is identified from the vehicle shadow;

estimating, in response to the front vehicle shadow being determined to be identified from the vehicle shadow, a position of a second preceding vehicle traveling in the traveling lane and belonging to the train of the vehicles including the first preceding vehicle on a basis of the front vehicle shadow, wherein the position of the second preceding vehicle is estimated by calculating a boundary between the road surface and the front vehicle shadow and setting a boundary frame;

estimating abrupt deceleration of the second preceding vehicle on the basis of an estimated position of a rear portion of the second preceding vehicle, wherein the position of the rear portion is estimated on the basis of the boundary frame of the front vehicle shadow; and

controlling, in response to the abrupt deceleration of the second preceding vehicle being estimated, of the own vehicle to deal with the abrupt deceleration of the second preceding vehicle by setting a target inter-vehicular distance between the own vehicle and the first preceding vehicle,

wherein the instructions further comprise:

estimating a position of the sun on a celestial chart with reference to the celestial data stored in the storage on a basis of a current date and time;

acquiring a traveling azimuth angle of the own vehicle identified by movement of the own vehicle;

setting an incident angle of sunlight on a basis of the position of the sun and the traveling azimuth angle of the own vehicle;

setting a rear outline of the first preceding vehicle on a basis of the recognized first preceding vehicle;

setting a possible second preceding vehicle region in which the second preceding vehicle is possibly present on a basis of the set rear outline of the first preceding vehicle and an infinite point placed in front of the own vehicle;

setting a vehicle shadow detection region on a basis of the set possible second preceding vehicle region and the set incident angle of the sunlight; and

identifying a shadow present within the vehicle shadow detection region as the front vehicle shadow;

determining whether a third preceding vehicle traveling is recognized on an adjacent traveling lane to the traveling lane on a sunlight incident side on the basis of the information on the traveling environment;

in response to determining that the third preceding vehicle is recognized on the adjacent traveling lane on the sunlight incident side, determining whether a shadow of the third preceding vehicle is present within the vehicle shadow detection region;

in response to determining that the shadow of the third preceding vehicle is present within the vehicle shadow detection region, not performing an estimation of the abrupt deceleration of the second preceding vehicle; and

in response to (1) determining that the third preceding vehicle is not recognized on the adjacent traveling lane on the sunlight incident side or (2) determining that the shadow of the third preceding vehicle is not present within the vehicle shadow detection region, performing the estimation of the abrupt deceleration of the second preceding vehicle.