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Motorway Traffic Flow Monitoring and Control

Objective

The principal goal of this project is to define and build prototypes of systems for ramp metering control and variable traffic information on urban (linear and networked) motorways. Ramp metering distributes a given demand in space and time by influencing traffic volumes (traffic lights); message signs can be used to inform drivers and so divert them onto alternative routes to prevent or reduce congestion.
The existence of adequate macroscopic mathematical models for freeway traffic is a prerequisite for the development of traffic monitoring and efficient control strategies. 2 macroscopic traffic flow simulation models (SIMAUT and META) for linear motorway, one based on the kinematic wave theory and the second based on a state space framework, have been selected for improvement and comparative assessment on a linear motorway based on real data from 2 French sites and 1 British motorway.

Linear simulation was then extended to motorway networks with 2 simulation packages being developed. The network simulation program METANET was extended and improved to give simulation tool for broad use. METANET uses a macroscopic modelling approach to consider multiple origin, multiple destinations and network phenomena. The computational effort is low, hence the model can be used online for monitoring and control purposes. The development of a motorway network version of the well known simulation package CONTRAM, called MCONTRM, was completed with validation studies. MCONTRM is capable of calculating dynamic traffic assignment for use in route guidance. Moreover this tool is used within the aid to decision approach to motorway control.

2 approaches to motorway traffic control have been considered, aid to decision and fully automatic control strategies. The aid to decision approach is based on the use of an online traffic simulation model. It is implemented in the form of a knowledge based system and gives to the operator the opportunity to simulate the impact of the planned control actions on the traffic flow. The automatic approach is based on automatic control theory. The applied control law leads automatically to optimal decisions according to predefined criteria (eg queue length, travel time, etc).
The first step has been a review of different strategies used or tested for ramp metering both on an isolated and a coordinated level. A number of control strategies have been further improved and assessed in order to be implemented in the field. With concern to motorway network control, 2 entirely new control strategies (one based on automatic control concepts and another using aid to decision and expert system tools) have been developed and tested by simulation means for hypothetical scenaria and for existing motorway networks.

A number of field trials on motorway ramp metering have been designed, executed and evaluated at 2 different sites.
These field trials have been extremely useful for various reasons:
increasing confidence in the usefulness of ramp metering in general and in the effectiveness of particular control strategies;
more insight and understanding could be gained on the functioning of each control strategy and on the similarities and the differences between them;
a number of software prototypes have been produced;
a number of practical recommendations and generalised experience have been gained.

Twenty subjects were provided with in car route guidance equipment, and then drove between a preselected set of origins and destinations in Athens, both with and without the benefit of the route guidance. Most of the participants had no substantial predisposition for or against route guidance. They expected that it would be useful to them when driving in unfamiliar areas, but not in familiar areas, unless it provided real dynamic information on traffic conditions. Oral information was preferred to visual information, though some participants preferred a combination of both.
The research focuses on two points:
- Motorway traffic flow modelling.
Existing models will be improved and adapted to real-life conditions and extended to cover motorway networks.
- Motorway traffic flow management and control.
Two approaches will be investigated - advisory and fully automatic control strategies. Advisory systems allow the operator to simulate some strategies and to choose the `best' according to human experience. Automatic control strategies, based on the theory of optimal control, lead to optimal decisions according to pre-defined criteria (e.g. queue length, travel time etc.).
This theoretical and experimental investigation will include implementation considerations such as alternative measurement and control devices, computer hardware facilities, communication media, system architecture, and man-machine interfaces. Special attention will be paid to system flexibility with respect to the future development of a route guidance facility.
Prototypes both for local and coordinated control will be created. `Real life' experiments for both types of on-ramp metering will be performed at selected sites.
Main Deliverables:
Prototypes for linear & network motorway control; results of simulation study and software specifications.

Coordinator

Institut National de Recherche sur les Transports et leur Sécurité (INRETS)
Address
109 Avenue Salvador Allende
69675 Bron
France

Participants (7)

RIJKSWATERSTAAT
Netherlands
SCETAUROUTE
France
Address
2 Rue Stephenson
Saint Quentin-en-yvelines
SIAT
France
TRANSPORT RESEARCH FOUNDATION T/A TRANSPORT RESEARCH LABORATORY
United Kingdom
Address
Old Wokingham Road
RG11 6AU Crowthorne
TU THESSALONIKI
Greece
Technische Universitaet Muenchen
Germany
Address
Lichtenbergstrasse 4
85748 Garching
Wootton Jeffreys Consultants Ltd
United Kingdom
Address
Brookwood
GU24 0BL Woking