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Traffic quality and capacity of freeways (VSS2000/337)

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Complete with results
Geo-spatial type
Network corridors
Project website
STRIA Roadmaps
Network and traffic management systems (NTM)
Infrastructure (INF)
Transport mode
Road icon
Transport sectors
Passenger transport,
Freight transport


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


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.


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.


Parent Programmes
Institution Type
Public institution
Institution Name
Swiss Government: State Secretariat for Education and Research
Type of funding
Public (national/regional/local)


Major importance is attached to optimum design of additions to the network in motorway construction in view of increasing overloading and shrinking road-construction budgets.

The VSS Standard 640018 "Capacity, Traffic Quality and Loading Capacity", approved in 1999, represents an initial important step towards a differentiated basis for design. The capacities which it stipulates are based on older Swiss guideline values and foreign standards. It is not based or is hardly based on empirical surveys from Switzerland.

The results of this project are: elaborating updated values for the capacity in accordance with Swiss conditions deriving corroborated interrelationships between parameters of traffic flow on the one hand and main influencing factors on the other and providing standard fundamentals in the form of load-speed curves (q-v curves).

This is based on the current manuals from Germany (HBS) and the USA (HCM) in addition to more recent literature on the one hand and empirical measurements on the other. It can be seen that it is difficult to obtain series of measurements with traffic loads in the region of maximum capacity for assessment of all important influencing factors. Consequently, what is necessary is an additional systematic investigation of the influencing factors using a simulation model. It has been use used the VISSIM program package for this purpose. Both individual patterns over time and the results of the evaluations of the empirical data are used to calibrate the model.

The results of the analyses of the empirical data and of the simulation are complementary so that we have a good founded basis for revision of the Standard. The empirical data does not indicate any regional differences in relation to the important traffic volumes. By contrast, it indicates that there may be differences between conurbation traffic and interurban traffic. The capacities to be defined should be based on the conurbation traffic since this type of motorway is dominant in Switzerland referred to peak capacity and problematic sections.

The existing differences in traffic volume between conurbation and non- conurbation should be allowed for when revising the Standard on the basis of the quality level of traffic flow. Gradient, heavy good traffic share and speed restriction should be viewed as essential parameters for design of high-capacity roads. They are based on the results of the simulation and evaluation of empirical data. The capacity for a two-lane or three-lane cross sect


Lead Organisation
EU Contribution
Partner Organisations
EU Contribution


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