The northeast New Jersey route guidance system (RGS): Case study of a distributed system

The general trend in the computer industry today is moving from centralized toward distributed processing. The same trend is impacting the traffic-control field and is being fueled by the availability of low-priced microprocessors in a general environment of increasing communications costs. The Northeast New Jersey Route Guidance System (RGS), now in the final design phase, serves as an example to illustrate the reasons behind this current trend. One of the major decisions facing the traffic-control system designer concerns the selection of the communications system to be used between a central control base and the remote controllers/processors. Whereas in the past it was possible to separate communications system design decisions from control design decisions, such separation is no longer possible. A portion of the decision is outlined by which a 1972 recommendation for central control, made as part of a surveillance-and-control system feasibility study, was modified to distributed control in 1977, during the preliminary design phase of that project. Five communication alternatives, analyzed for use in the RGS, are described. Two of the five alternatives, requiring the least expensive communication-media leasing costs, entail distributed rather than central control.