The objective of the project is a development of pre-standards in accordance with SN 641000. Principles and definitions, as well as eight elements of transport facilities.
In the method for determining the performance of the transport quality and capacity, three approaches can be distinguished:
• Offer-oriented methods:
At a given transport supply is - taking into account the carrying capacities - the manageable traffic volume determined.
• Demand-oriented methods:
For a given traffic volume is - taking into account the carrying capacities - the transport supply needed determined.
• Performance analysis:
If both supply and demand are given, the traffic quality is the performance analysis determines and assesses the capacity.
The present research project provides transportation and traffic practitioners with improved methods for the calculation of capacity, level of service, and environmental tolerance of transportation facilities. It is based on results published in report no. 276, which presented the concepts and methodologies for the design of transportation facilities.
In the 90’s, a German manual for the calculation of the capacity and for the evaluation of the levels of service for various street and highway facilities had been created. During the same time the U.S. Highway Capacity Manual (HCM) has seen two new editions (HCM 1994 and HCM 2000). Even in Switzerland many research studies concerning the field of capacity and level of service have been produced.
The new Swiss reports had to be analysed, compared with results of recent foreign studies, and combined into new standards that can replace the old SN 641 145 standard from 1973. The methods presented here offer the possibility to perform the calculations without computers for the following standards concerning capacity, level of service (LOS), and environmental tolerance.
• Basic information:
Methodologies are presented for traffic-flow analysis, capacity calculation, flow service rates connecting to the various levels of service, and the environmental tolerance.
• Basic freeway segments:
Basic freeway segments are outside the influence area of ramps or weaving areas of the freeway. For such segments, the report presents data for four-lane freeways (two lanes in each direction) and six-lane freeways (three lanes in each direction). The calculations consider the influence of lane width, the lateral clearance, the specific grades, and the percentage of heavy vehicles. The density defines the LOS. The capacities are lower than those given in manuals of other countries. One of the reasons are the speed limits that depend on the type of vehicle on the same freeway segment.
• Freeway ramps:
The data are given only for ramps onto four-lane freeways. The calculations are based on the traffic volume in the right lane right after the merging area. The density also defines the LOS.
• Highways outside built-up areas:
The capacity depends on the percentage of heavy vehicles, the specific grade, the frequency of curves, and the percentage of no-passing zones. The availability of certified data is insufficient to define levels of service. However, the report provides ca