As an example of integrating signal control with network traffic assign- ment, the notion of path-based signal coordination in transportation net- works is introduced and illustrated. The use of a real-time dynamic traffic assignment system allows prediction of the traffic flow patterns and iden- tification of the dominant paths in the network. The signalized intersec- tions along these paths, which may consist of combinations of straight sections and turning movements, are coordinated to increase the capac- ity of the freeway and the surface street system to efficiently absorb diverted traffic from the freeway. A set of experiments is designed to compare the network performance under the path-based coordination scheme with no coordination and arterial-based coordination. The experi- ments are conducted for both pretimed and vehicle-actuated signal con- trol. An actual network, which represents the south-central part of the Fort Worth area, is used in these experiments. The network consists of a freeway (I-35W) surrounded by a street network with a total of 178 nodes and 441 arcs. The path-based coordination scheme is shown to outper- form arterial-based coordination in the cases of both pretimed fixed con- trol and vehicle-actuated signal control. A significant reduction in the network average travel time under the path-based coordination scheme is observed compared with the other schemes. This application further illustrates the benefits of real-time dynamic traffic assignment for advanced traffic management under incident conditions. Real-time dynamic traffic assignment (RT-DTA) is a core method- ology for the operation of Intelligent Transportation Systems tech- nology in the management of traffic networks to alleviate both recurrent and nonrecurrent congestion. Used in conjunction with incident detection capabilities, the RT-DTA system is intended to predict the traffic flow pattern and provide decision support capa- bilities in the generation of information to users (for route diversion selection) and the evaluation of alternative traffic controls. Efficient use of the available capacity in the highway corridor network through integrated operation of the freeway and the surrounding sur- face streets is a major objective of incident management schemes. In response to real-time information and route diversion advice via variable message signs (VMSs) upstream of the incident as well as various on-board devices, freeway users may divert to the surface street network. To absorb the diverted traffic, the capacity of the sur- face street network should be optimized by modifying the traffic signal control to serve the new flow pattern. Prototypical advanced traffic management system schemes en- vision signal coordination along the freeway frontage roads (if available) or along parallel arterials to provide a through band of progression for through traffic along these facilities. However, diversion traffic may not necessarily follow a through path along these major parallel facilities. Instead, diversion paths may involve TRANSPORTATION RESEARCH RECORD 1667 Paper No. 99 -1228 67 turning movements at key junctions. Incident management and coordinated network control can be considerably more effective if they recognized these flow patterns and favored dominant move- ments through the network (e.g., by providing coordination to achieve a through band for particular paths followed by these dom- inant streams). Such an approach is referred to as path-based signal coordination. One of the difficulties of providing such path-based coordination is to identify the particular path along which coordination should be provided, especially in dynamic environments such as nonrecurrent congestion spots. Recent developments in dynamic assignment, especially the RT-DTA capabilities mentioned earlier, make it pos- sible to extract such paths from the solution (i.e., from the predicted flow patterns in the network). This paper has two objectives: (a) to illustrate the benefits of coor- dinated network operation under incident conditions, with particu- lar emphasis on path-based signal coordination; and (b) to describe procedures for identifying paths along which coordination would be beneficial, given RT-DTA capabilities, and for implementing such coordination schemes. Although traffic signal coordination is a topic that has been exten- sively covered in the literature, it does not appear that path-based coordination has been described and tested. Nevertheless, its essence lies in some of the early seminal work of Gazis (1) and Gazis and Potts (2) on signalized network control, which discussed conceptu- ally the potential of combining routing with signal control for effi- cient use of a traffic network. This approach may be viewed as a natural step from straightforward arterial progression toward the more complex problem of network coordination in the case where dominant flow patterns can be identified. First, the RT-DTA system used in this paper is described. The notion of path-based coordination along paths that combine con- secutive through and turning movements is introduced. Numerical experiments on an actual network are designed to evaluate the net- work performance under path-based coordination compared with the do-nothing base case and with arterial-based coordination, for both pretimed and vehicle-actuated signal control. The experiments also illustrate the role of real-time information through VMSs in incident network management and the decision-support function of RT-DTA in this process. BACKGROUND AND GENERAL APPROACH The RT-DTA capabilities illustrated in this paper are provided by the DYNASMART-X simulation-assignment system. Its structure, Real-Time Dynamic Traffic Assignment and Path-Based Signal Coordination Application to Network Traffic Management KHALED F. ABDELGHANY , DIDIER M. V ALDES, AKMAL S. ABDELFATAH, AND HANI S. MAHMASSANI Department of Civil Engineering, ECJ 6.2, The University of Texas at Austin, Austin, TX 78712.