Traffic quality and capacity of freeways (VSS2000/337)
Overview
Background & policy context:
When selecting suitable counting stations and the subsequent analysis shows that it is difficult to obtain measurements with traffic loads in the area of peak power to assess all important factors (number of lanes, longitudinal slope, cross-sectional shape, traffic composition and speed limits). There is need for a systematic study of the complementary factors with the help of a simulation model. The results of the analysis of empirical data and simulation complement each other so well hedged basis for the revision of the standard are available.
The empirical data were no regional differences in the authoritative traffic volumes can be recognised. By contrast, emerge from the empirical data evidence that there are differences between urban transport and inter-city transport. The capacity to be determined should be based on urban transport, as this highway type based on the power peak and dominates the problem stretches in Switzerland. The existing differences in traffic volume between metropolitan and non-metropolitan area should be covered by the standard revision on the traffic quality level.
As an essential parameter for the design of high-performance roads the slope, the proportion of heavy traffic and the speed limit must be considered. The two-lane or three-lane capacity for a cross-section is located at a slope of 1% and an LW-share of 0-5% in 4000 Mfz / h or 5800 Mfz / h. These maximum values are realistic and adequately covered by the empirical data material, but put a vehicle distance of less than 2 seconds ahead.
Recent studies come to the conclusion that the capacity of a road traffic system have different values and this may vary significantly. A breakdown of the traffic flow is carried out not at a fixed value, but a wide range of traffic volume. It is therefore characterised as a random event with a large scatter. Detailed studies for the station N1 / Regensdorf (Zurich northern bypass) on the likelihood of collapse confirm this hypothesis. In the revision of the standard will continue to assume a fixed value for the capacity. Relations between capacity and breakdown probability that could not be treated only as an example in this work are to delve into further research.
The traffic volumes are determined on inclines of less than 3% and LW share less than 15% in principle, comparable to those of the German HBS. With steep slopes and higher LW share significantly higher values are detected during the simulation results both at the two as well as the three-lane cross
Objectives:
The objective of the project is a development of current capacity estimates for the Swiss motorway network, with special attention to impact of gradients and heavy truck traffic.
Methodology:
The methodology to derive the values for the performance on Swiss motorways on the one hand from empirical data and on the other hand with the aid of a calibrated simulation model, has been correct and convincing both from a theoretical as well as from a practical perspective. The determined QV curves are well covered under the existing state of knowledge.
Recent findings indicate that the capacity of roads is to be regarded as a random variable, have been taken up in the work and examined representative examples and considered. This latest approaches to delve into further research to assess the consequences for the entire standard-group better.
The notice also an update of the guideline for the maintenance-related strength was demanded. This concern could be rudimentary taken into account-in the context of work.
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