Clear Vision.
—Clear vision is another thing that should be insisted upon as a means for safety. Weeds, brush and trees are all too frequently allowed to obscure the sight. With ordinary brakes on smooth roads from 100 to 150 feet is needed to stop a car moving at 30 miles per hour. With first-class brakes this might be decreased, but since it usually takes a driver a short period to react from the time a car heaves in sight or he sees a break in the pavement or some other obstruction, there should be allowed 150 feet to stop if the roads are smooth and hard. In order that there might be a good factor of safety it is desirable to get at least 250 feet clear vision. This will require for a 200-ft. radius that the brush, trees and so on should be cut back about 27 feet from the traveled way. As the radius becomes larger the distance necessary to clear back becomes less: 300-ft. radius, clearance, 12 ft.; 400-ft. radius, 7 ft.; 500-ft. radius, 4 ft. In case the curve is in a cut the bank on the inside at the height of the eye should be excavated far enough back to give the necessary clear vision.
At the corners of city streets it will, of course, be impossible to get a 200-ft. radius. A 12- or 14-ft. radius may usually be obtained. The rule to turn close to the curb may then be accomplished with the ordinary automobile providing it is not going very fast. With a square angle or a short 2- or 3-ft. radius as it was formerly the custom to put in, and still is in places, it is practically impossible to keep from going at least to the middle of the street thus endangering motors on the other side. The cut shows the lines of travel.
Diagram to show why curb corners should be cut back.