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.
The research goal is to develop principles for assessing the quality of the traffic flow in the upper performance range. The determination and calculation of the relevant parameters of the traffic flow is carried out in connection with various forms of design.
The determination and calculation of the relevant parameters of the traffic flow is carried out in connection with various forms of design.
The investigations led to the following main findings:
1. Performance one traffic lane gyroscope one traffic lane driveways (Type 7/7):
The existing tax relationship between the traffic volume on the county road and the maximum possible traffic volume of the entering traffic of access in accordance with SN 640 024 was largely confirmed.
2. Performance one traffic lane gyroscope about wide circular road and two traffic lane access (Type 2/9:
This in Switzerland frequently used and deems appropriate operational form, as supposed to a higher efficiency in comparison with a similar diameter rotors and one traffic lane county road in one traffic lane access. The determined with reference to various roundabout this type of operation average increase in performance of the access is considerable 20 to 40%. The newly developed design context can be seen in the following figure.
3. Influence across Ender pedestrians on the performance of the access:
The earlier finding that the impact across Ender pedestrian decreases the efficiency of the approach with growing traffic volumes on the county road, could be confirmed. As traffic volumes exceeding 800 vehicles per hour on the circular road performance the approach is practically not reduced.
The investigation showed, however, that at low traffic volumes on the circular road of the impact on the performance of the access even at already low pedestrian volumes significantly greater, namely approximately doubled compared to the previous bases of assessment, fails. This influence has been obvious, especially at low to medium traffic volumes on the county road, underestimated. An adaptation of the standard SN 640 024 in this area suggests itself.
The findings of this study provide the basis for an addition to the standard SN 640 024 one traffic lane area centrifugal with about wide circular road and two-lane county access roads as well as an adaptation of the basics in order to reduce the performance of centrifugal driveways due to cross Ender pedestrian. No base yet could be developed for operating mode two-lane roundabout with two-lane access roads.