Combining in-vehicle routing and traffic control systems.

The current first generation of in-vehicle routing systems provide only static information to drivers. This is understandable, considering that the world's traffic control systems, which are relatively far more mature, are still predominantly fixed-time systems. In fact the United States still doesn't have a single signal network controlled in real time. However, second generation in-vehicle routing systems, which will provide navigational information to vehicles in real time based on component link costs corresponding to "current" conditions, are already being designed and field-tested. In the relatively recent past, a variety of real-time network traffic control systems have been cropping up. The current real-time systems do not consider the type of information that will be available in real-time driver routing systems. At the same time, in-vehicle routing systems are relying more on history of the type provided by probe vehicles than on predictive information obtained from detecting vehicles upstream of the point at which they are to be controlled. The routing and control systems provide different types of advance information, each of which has its own advantages. In addition to their own use for routing drivers to their ultimate destinations, these navigational systems can also calculate arrival times to various locations in the network for use by traffic control algorithms. This can in turn assist the traffic control system in providing in-vehicle routing systems with not only shorter, but also more predictable trip times. The real-time routing system can also use such information itself, to improve the reliability of its real-time routing information. In other words, by providing demand information to the traffic control sub-system, the routing sub-system helps itself. Only through co-operating can two interacting sub-systems hope to approach overall optimal operation. The first level of co-operation is to pass information between the sub-systems, and the ultimate level is to operate them as a single integrated system. The respective requirements and potential for co-operation between these different sub-systems are addressed and discussed in detail in the paper. (A)