There was identified the research need of assessment of the effect on the driving style and traffic, to point out benefits, possibilities, limits and conditions when utilizing mini-roundabouts.
The objective of the project is to define the basics for a traffic engineering and economic point of view (criteria) for mini-roundabouts.
Following activities will be provided during the project:
Literature review, inventory taking into account previous surveys by BFU, overall evaluation of the mini roundabout in Switzerland with regard to system data and accident statistics, sampling according to specific criteria, field test with detailed surveys (traffic counts, speed, observation, accidents, etc.) at the mini roundabouts in the sample, comparison of the system data in mini roundabouts with high and low accident, deriving recommendations for project elements, final report.
Mini-roundabouts represent discrete traffic facilities with associated requirements in terms of planning, design, and execution. In many situations design elements cannot be based on the standard specification, so that particularly thorough coordination is required.
Application option assessments for mini-roundabouts have to take into account operational, installation and peripheral influences. The following requirements regarding location, function and junction type should be considered:
The design of the geometric elements of mini-roundabouts can generally only satisfy minimum requirements, so that this type of roundabout is only recommended for urban roads with a speed limit of 50 km/h. Due to the reduced dimensions of mini-roundabouts, they should not be used as 'gateways' on strategic roads (speed-reducing design elements between non-urban and urban roads).
Mini-roundabouts are generally suitable as interfaces between roads with the same hierarchy level. Mini-roundabouts are less suitable as interfaces between main and subordinate roads (e.g. local distributor roads or access roads). In addition, mini-roundabouts should be avoided near light-controlled junctions.
For mini-roundabouts with smaller dimensions than standard small roundabouts, a key parameter is balanced traffic loads on the access roads. The average traffic load on the subordinate road should be at least 25% (for junctions) or 30% (for crossroads) of the roundabout load (total traffic load entering and exiting the roundabout).
The total traffic load of the roundabout and the access should not exceed 1,300 vehicles per hour. In order to ensure safe traffic flow the proportion of heavy goods vehicles relative to the total traffic load must also be taken into account.
- Due to the smaller dimensions of mini-roundabouts, it may not be possible to meet all standard design requirements for midi-roundabouts. To ensure safe traffic flow the following design requirements must be adhered to or considered:
- The outside diameter should be as large as possible. Roundabouts with an outside diameter of more than 18 m may feature a central island and an over runnable ring. The outer edges of the access and exit sections must also be over runnable for heavy traffic.
- Mini-roundabouts with an outside diameter of less than 18 meters must not