The upcoming german guideline for calculating the capacity of unsignalized intersections is described. Information is included on fundamental aspects of the theory as well as on the proposed procedurethat results from several research projects carried out on behalf of the west german federal minister of transport. The new guideline will be a revision of the german procedure introduced in 1972, which has been transferred as chapter 10 of the 1985 highway capacity manual (hcm). Furthermore, a selection of formulas for roundabout capacity is given. Capacity and delays of unsignalized intersections have been investigated in germany in a long series of research projects during the 1960s and 1970s. These results led to the german guidelineof 1972, which was mainly based on harders' pioneering work. The problems with the 1972 procedure and chapter 10 of the hcm can be summarized as follows: (a) differences to the simple poisson case, (b) concept and size of critical gaps, (c) determination of impedance factors, (d) double introduction of rank 2 and rank 3 traffic streams, and (e) delays and level of service. After the publication of the 1985 hcm, the problem of capacity at unsignalized intersections received new attention in germany. A series of research projects was started, and the aim of which was to develop a new guideline for practical application. The results of these investigations will be introduced into the german committee's discussions within a short time. This paper appears in transportation research record no. 1320, Freeway operations, highway capacity, and traffic flow 1991.
Abstract