The research unit develops scientific foundations for the derivation of reference values which allow a reliable assessment of the quality of traffic flow on streets without direction separation, especially in hilly terrain and in longer tunnels, taking into account Swiss conditions (traffic behavior, types of operation, speed limits, development standards, slope conditions). The examination should be carried out according to the procedure for traffic engineering design in the existing standards.
With regard to methods for determining the performance of the transport quality and capacity of transportation facilities, many questions remain unanswered when it comes to major and interconnecting roads. The appropriate standard SN 640 020 because even often still formulated very openly, knowing that the basics are sparse.
Due to existing and collected data and with the help of simulations benchmarks for performance and quality levels of traffic direction not separate roads should be developed. The influencing factors are to define and quantify. For traffic quality the decisive criterion is to be determined.
The project has following objectives:
- Scientific databases for standards
- Approximate values for the reliable evaluation of the level of service on undivided highways in particular in hilly area and in longer tunnels
Following steps are provided during the project:
- Surveys, collection and analysis of measurement data set simulation model
- Accrued influencing factors calibrated model
- The key criteria determined, defined dependencies of the influencing variables
- Completed research objectively provided a basis for standardization
- Created research report
Knowing about the limited research budget and the hence implied pragmatical procedure, the very large variety of possible road types has been limited to the following types:
• Highways outside built-up areas: Two-way roads with one complete lane per driving direction, divided by street marking, and with a general speed limit of 80 km/h.
• Two-lane motorways: Two-lane motorways with one lane in each direction, divided by street marking and operating according to the Swiss "Motorways" regime (usually applied to physically divided four-lane toll motorways).
• Longer tunnels: Tunnel sections of highways outside built-up areas or two-lane motorways without physical dividers and with speed limited to 80 km/h. The actual norm is missing numbers for describing traffic quality being shown by means of Quantity Speed Diagrams (Q/V Diagrams) as used in the German HBS 2001 and in the Swiss Standard for Motorways. After evaluation of the base data it became evident that these Q/V Diagrams had to be adapted to the Swiss circumstances. This is due to different speed restrictions in Germany, different speed of heavy vehicles in uphill sections, and the results more homogenous driving behavior. Roads with a traffic volume that use the whole value range are rather seldom in Switzerland. In spite of this, additional punctual measurements could be carried out on all three road types on "even and straight" sections (according to the reference state).
From the evaluation of these measurements, including older punctual measurements, it follows
• Almost linear curves in the Q/V Diagram (while traffic flow is stable) with a different speed level per road type. The curves for highways outside built-up areas and two-lane motorways differ significantly from the corresponding German curves.
• No traffic breakdowns caused by the segment itself, in spite of traffic flows close to saturation.
• Traffic problems before and after the observed sections. The two-lane sections are rarely a limiting element – at least in the reference state. Neighbor nodes or sections passing built-up areas mostly decide about the traffic load of these sections.
• Traffic flow disturbances below the theoretical capacity limit due to the "open system" on the highways outside built-up areas, by turning vehicles (in and out), bicycles, or pedestrians.
• Similar traffic loads close to capacity limit at the reference state of all three evaluat