Lateral Placement of Vehicles on Rural Roads

The purpose of this paper is to present the results of various studies which have been made concerning lateral placement of vehicles on rural roads. The term “lateral placement,” as it is used throughout this report, is construed to mean the position of the vehicle on the road in relation to either the right edge of the pavement or to the centerline of the road. Only two-lane roads will be considered in this report, unless otherwise specifically stated. A thorough knowledge of the average lateral placement of vehicles is very important to the highway designer, and various studies have been made in an effort to obtain information in this field. From the standpoint of safety, we assume that the wider the pavement, within certain limits, the safer it should be; but from the standpoint of economics, it is not feasible to build highways beyond certain widths. Roads which are too narrow result in excessive maintenance of the shoulders and dangerously reduce the clearance distance of passing vehicles, and two-lane roads beyond certain widths are used as threelane pavements by occasional drivers. Neither condition is to be de­ sired. For these reasons, the determination of the proper width of pavement to be constructed for any particular situation has become a problem that the traffic engineer should solve. Since 1920, there has been a steady increase of widths for newly constructed pavements. Simonson1, in his paper, gave a diagram of this trend. In 1920, the two-lane highway was constructed with a 16-foot width. In 1925, the average width was 18 feet, increasing in 1930 to 20 feet. After 1930, differing opinions arose, with the result that in 1935, new pavements were from 22 to 24 feet in width. Since the war years, more careful consideration has been given to the proper width of roadway for any given situation, and no definite value can