Planning and Geometric Aspects of Shared Streets

Abstract

The concept of “shared streets” involves an area in which the street is shared by pedestrians and vehicles. The entire shared street area is paved, and no vertical elevation difference exists between the walking areas and the parking area and the “travel lane.” The concept of travel lane is developed in this paper, and it refers to that part of the shared street that is specifically intended for motorists to travel. The travel lane is often distinguished by blocks with different colors. Because of the narrow lane width, it is possible for only one vehicle to pass through a straight section; two vehicles can meet only in the diagonal section. The angle of the diagonal section and the length and width of the straight section are primary parameters that strongly affect the travel speed along a shared street. Some general planning considerations are discussed, such as creating a discontinuous alignment by inserting a diagonal section between two consecutive tangent sections. Unidirectional or alternating diagonals are discussed, and three general forms of diagonal sections are presented. Safety considerations are also discussed, along with the need to provide sufficient parking space for visitors and residents. It is shown that the geometry determines the path of vehicles that results in a possible safe speed for a given design. Specific design criteria are presented for the recommended length of a tangent section and the recommended minimum width ranges, depending on the length of street. The parameters determining the geometric characteristics of the diagonal section, the angle of turn, the offset between the centerlines of the two adjacent tangent sections, and the width of the road along the tangent and within the diagonal section are also presented and evaluated. It is concluded that shared streets provide an excellent, attractive accessibility solution for residential neighborhoods with low volume of residential traffic resulting from a low density of residential dwellings. If planned properly, a balanced design is achieved, and the reduced speed results in improved safety and enhanced environmental qualities.