| The increase in used capacity of existing freeway networks is an important improvement that can be accomplished by the use of an effective control system. The average travel time for a motorist, and the reduction of energy consumption are just two examples of the benefits that an effective control system may provide.;A multilevel (decentralized) control scheme with application to the regulation of traffic on a freeway, the cascading technique, that avoids the problems mentioned and that improves reliability, sensitivity and ease of computation is presented in this research.;The freeway is modelled in terms of the aggregate variables, section density and mean speed, and considered as an interconnection of several subunits.;The control problem is divided into two parts: design of a set of local controllers for the individual sections, and a controller at a higher hierarchical level that will provide control signals to account for the loss of one or more controllers.;During the past two decades, traffic engineers have dealt with the problem of freeway regulation from a centralized point of view: every sensor output affects every actuator input and all the information is available to every actuator. This setup is costly, transmission lines from each of the sensors to the central processor are needed and the associated mathematical optimization problem is highly difficult and time consuming.;For estimation an extended Kalman filter is used, where the filter operates on the detector data sequentially, generating new state estimates as new observations become available, opening the possibility for real time estimation. For converting presence detector data into measurements of the aggregate variables a new estimating technique is introduced.;The solution to the freeway problem is a control policy that establishes the on-ramps flows for every sampling interval, and this policy is a closed loop control.;The cascaded control technique and the freeway model are applied to a section of the San Diego freeway in Los Angeles. Simulations are shown where an incident occurs and the performance of the cascading technique, centralized control and fixed time metering are compared. It is also shown that under loss of information the cascaded structure performs better than the centralized one. |
