When reading a book this may only be a width of 2 or 3 words; however, at a 150 feet tis about 8 feet. Technically our eyes do not actually scan at a constant velocity, they saccade. Saccade is the rapid eye movement between fixation points of focus. Interestingly, our brain automatically disconnects during saccades so that our vision is not blurred. These are some of the reasons the degree of visual excentricity of an intruding object or vehicle increases our perception response time.
Just sayin' . . .