APPLICATION AND TESTING OF THE DIAGONALIZATION ALGORITHM FOR THE EVALUATION OF TRUCK-RELATED HIGHWAY IMPROVEMENTS

Highway and transportation officials are increasingly concerned about accommodating rising truck traffic and the associated size and weight trends. A network traffic assignment procedure is an essential component of the methodological support for the identification, evaluation, and selection of truck-related physical and operational improvements in a highway system. A general mechanism is presented for the network representation of improvements consisting not only of physical capacity expansion but also corresponding operational strategies in the form of (existing or new) lane-access restrictions to either vehicle class; this mechanism allows the consideration, as a special case, of exclusive truck lanes or facilities contemplated by several agencies. The special requirements of the traffic assignment procedure in this context, including the need to explicitly consider the asymmetric interaction between cars and trucks, give rise to potentially serious methodological difficulties that must be addressed for specific types of applications. The applicability of the diagonalization algorithm to such problems is investigated by using numerical experiments on three test networks under varying conditions. The three test networks include an abstracted condensed representation as well as a full-scale version of the Texas highway network, thus providing a realistic case application. The main aspects of the algorithm's performance addressed in these experiments are its convergence characteristics as well as the effectiveness of some computational streamlining strategies. Although convergence is not guaranteed a priori, it was actually achieved in all test cases. Furthermore, it is shown that shortcut strategies can considerably reduce the algorithm's computational requirements.