The effects of motorway ramp metering on the secondary road network are examined. Alternative ramp metering strategies are evaluated for different network typologies with respect to different criteria (traffic safety, network fluidity on the motorway and the secondary network, equity). A method for checking the suitability of different metering strategies and other traffic measures for alternative network typologies is needed to developed and tested for practical cases with the help of microsimulation.
The goal of the project is it to develop a method for the evaluation of alternative ramp metering strategies and to determine the most appropriate measures to reach the best overall benefits (in terms of traffic safety, traffic flow throughput and equity) on the whole network. The most frequent network typologies, traffic conditions and ramp metering strategies will be set into a relation and possible effects will be examined.
The result should allow:
- to pre-determine the local effects of ramp metering
- to check the compatibility of motorway ramp metering on the secondary network and to determine possible limits
- to develop the optimal motorway metering strategies and the applications spectrum for measures on the secondary network.
The activities provided during the project are listed below:
- To study of literature and internet search on spplications of ramp metering with special attention to the impact on the subordinate road network.
- To provide list of different management strategies (eg priority traffic flow HLS, Preventing backflow to HLS driveway etc.)
- To provide an accident analysis and analysis of traffic figures (velocity, density of traffic) on the parent and child network in areas with and without ramp metering.
- To work out the analysis of the degree of concern for various driving categories, analyzing the differences and develop a degree of diameter for distributive justice ("Equity").
- To prepare transport technical analysis of the types of networks, development of action plans
- To provide analysis of practical applications and micro simulation to test the impact of proposed management strategies and traffic engineering measures.
Experiences in Switzerland with ramp metering have shown that the implementation of metering measures in motorway entries generally causes a shift of traffic between 15 to 20% to non-managed junctions or to alternative routes in the primary distributor network. Size and dimension of the shift depend strongly on local conditions (distance to the next non-managed junction, existing alternative routes in the primary distributor network, travel time loss) and on the types of ramp metering (splitting groups of vehicles or a systematic retention of vehicles to shift congestion from motorway to the entry ramp). To clarify the effects on the primary distributor network with ramp metering an iterative procedure has been developed.
By means of a morphological box and based on twelve criteria, the essential effects on the primary distributor network with ramp metering as well as possible measures to reduce or compensate undesired effects have been composed and described. While some of these criteria could be quantified, most of them could only be rated qualitatively. Numerous interactions and connections exist between the criteria. The morphological box pools the results of the research work and represents a planning tool.
The developed procedure to determine the shift of traffic and the linked effects of ramp metering represents a pragmatic and useful instrument to clarify the need and choice of measures as well as to determine its effects.
For planning and implementation of future ramp metering, the following operational principles could be listed:
- The planning of future ramp metering may not only happen exclusively from the angle of the motorway, but also the aspects of the primary distributor network have to be taken into account at an early stage, particularly with regard to the shift of traffic.
- Future feasibility studies for ramp metering must also include the requirements of the primary distributor network.
- All affected communities and institutions already have to be included during the planning phase.
- Wide information and public relations campaign concerning the planned ramp metering increases the understanding for this measure of traffic management by the affected road users.
- For specific control of traffic flows both towards metered entry ramp and towards possible alternative routes, the secondary up-stream junction has to be equipped with vehicle actuated traffic lights.
- The attraction of possible alterna