Today's roundabouts in Switzerland often operate at the limit of capacity during peak-hour periods. The adverse effects are prolonged delays, queues, as well as increased emissions and fuel consumption.

Under these conditions all well-known analytical and empirical methods show problems to estimate the quality of the traffic flow.

From experience it is known that there are wide ranges when capacities are estimated using different methods. The differences between the individual methods are probably due to different driver behaviour and driver characteristics, and/or due to various types of geometric roundabout layouts in different countries.

Although a large number of roundabouts of various layouts are implemented (one-lane or two-lane roundabouts, with or without guidance for public transport or bicycles, in urban or rural areas, etc.), there is only a meagre number of suitable data sets available for research. Therefore appropriate campaigns to collect data on driving behaviour at the various types of geometric roundabout layouts need to be carried out. Obviously these campaigns should meet the current standards of traffic engineering.

The aim of this research is to acquire a basis for the evaluation of the Level of Service (LOS) of traffic flow in conditions close to capacity.