Vehicle driving assistance apparatus

A vehicle driving assistance apparatus mounted in a vehicle. In the apparatus, a drivable route detection unit detects a drivable route, a vehicle state quantity detection unit detects state quantities of the vehicle, and a steering control unit controls steering of the vehicle. Further, in the apparatus, an allowable region estimation unit estimates a driving allowable region on the basis of the detected state quantities and a predetermined allowable range of behavior of the vehicle. A deviation determination unit determines that the vehicle will deviate from the drivable route when a minimum width of an overlap region of the drivable route and the driving allowable region is less than a predetermined threshold. An intervention instruction unit then outputs to the steering control unit an intervention control signal to control steering of the vehicle.