A method for determining potential collision with another vehicle by a vehicle equipped with a vision system includes providing, at the equipped vehicle, a vision sensor including a camera and at least one non-vision sensor, and determining presence of a leading vehicle ahead of the equipped vehicle. A time to collision to the leading vehicle is determined based at least in part on a determined distance to the leading vehicle and a determined relative velocity between the equipped vehicle and the leading vehicle. A braking level of the equipped vehicle is determined to mitigate collision of the equipped vehicle with the leading vehicle. A weighting factor is employed when determining the braking level, and the weighting factor is adjusted responsive at least in part to determining, via processing of image data captured by the camera, that a brake light of the leading vehicle ceases to be illuminated.