Current VSS standards for the design and evaluation of uncontrolled intersections only take into account conflicts between private vehicles. Unfortunately, this limits the applicability of the standards in most Swiss urban networks, as they cannot be used to model other modes such as public transport, pedestrians, or bicycles. To address this issue, a new analytical method was introduced in a previous VSS research project (VSS 2008/301). The methodology to evaluate uncontrolled intersections used as an input the saturation flows of the different transport modes, the actual demands, and the priorities among them.
The goal of this project was to empirically verify the proposed methodology, and further simplify and improve it. In order to do that we collected over 40 hours of data in 23 intersections throughout Switzerland. Data was collected with the aid of video cameras and was later processed manually. The empirical data was used to define typical (default) values for the saturation flows of different transport modes (buses, trams, private vehicles, pedestrians) in urban settings in Switzerland. The data was also used to test the methodology proposed in the VSS 2008/301 report, and to improve it. Based on the results obtained, some modifications to the methodology were introduced in order to more accurately determine delays and queue lengths of individual traffic streams as a result of interactions between multi-modal traffic streams. This modified method also presents a tree-like structure that allows users to check for all possible scenarios with an easy to follow approach. This structure determines the effective capacity for each traffic stream as a function of the percentage of time for which they would be able to use the available road-space at the intersection.
Overall, this project contributed to the development of a new innovative methodology for designing and evaluating uncontrolled urban intersections. The methodology was implemented in a ready to use, user friendly excel program, so that the performance of uncontrolled complex interactions can be easily analysed and modified as needed. In addition, the process was clearly detailed and recorded so that new VSS standards/norms can be written in a near future.