Speed influences how noticeable differences occur, how long they are seen, and, hence, whether they are observed. Subtle cues need a slow pace, yet driving is not only fast, but it also demands concentration, leaving little time or capacity to appreciate the environment. If people who move quickly are to be able to perceive objects and people, representations must be enlarged greatly. Therefore the automobile city and the pedestrian city have different sizes and dimensions. In the automobile city, signs and billboards must be very big and bold to be seen.
Buildings are comparably large and poor in detail.
There is a disproportionate relationship between speed and the severity of pedestrian injuries. The total required stopping distance increases by a factor of somewhat more than three when vehicular speed doubles from 20 to 40 mph. Due to driver reaction time, a vehicle traveling 20 mph will travel approximately 73 feet before it even begins to slow down from the effects of a braking action. At 40 mph, this reaction-distance doubles to 147 feet of vehicle travel before the vehicle begins to slow from braking. The total kinetic energy associated with a moving vehicle is related to the square of the velocity of that vehicle.