A need exists during the application of freeway corridor control models to determine the prevailing origin-destination (OD) matrices for each time slice during the peak period to be analyzed. As it is virtually impossible to obtain these matrices directly by survey, a fully automated approach is proposed that would use Freeway Traffic Management System (FTMS) data already being collected. This approach relies on existing algorithms for formulating synthetic OD counts from observed link flows, but uses a special relationship that exists between OD matrices for consecutive time slices to carry out these computations more efficiently and often also with greater accuracy. The general background to the problem and the general solution approach that has been proposed are discussed. Subsequently, several different analysis runs using the proposed approach are described that were performed with data for the Burlington Skyway FTMS system in Ontario. The results of these runs illustrate the details of the technique and demonstrate the main reasons for the improved efficiencies and accuracy. The paper is concluded with a discussion of how the procedure can be further refined and implemented in both its off-line and on-line modes within existing FTMS installations.