In response to growing freeway congestion problems in the seattle area, the washington state department of transportation (WSDOT) initiated a ramp-control program in 1981 as part of a region-wide transportation system management effort. The ramp-metering system is a computer-based, distributed intelligence system that consists of field-located microprocessors and a centralised computer system. It is an integrated, traffic-responsive metering system. The system uses an algorithm that calculates metering rates in real time based on systemwide traffic conditions. The algorithm is simple in its approach but very effective in its application. The system has proven to be effective in a series of ongoing evaluations. In this paper, the WSDOT realtime ramp-metering algorithm is described. First a brief description of the seattle area freeway system and an overview of the development of the ramp metering system are provided. The components of the surveillance, control, and driver information system are then described, followed by a description of the physical elements of the ramp-metering system. After the realtime algorithm used, the limitations of the algorithm, and the advantages of the algorithm are described, the results of an ongoing evaluation effort are presented. Finally, further actions being planned are described.
Samenvatting