Validation and use of equilibrium network assignment for urban highway reconstruction planning

Abstract

The need to rehabilitate interstate highways and bridges will increase tremendously in the next decades. Due to traffic restrictions imposed during construction, these rehabilitation activities will cause major disruptions in existing traffic patterns. In order to develop mitigation strategies to reduce such travel impacts, reliable forecasts of likely travel pattern changes would be beneficial. In this paper, we examine the suitability of using an equilibrium traffic assignment model to predict the impacts of a major highway reconstruction project. A case study of travel impacts during reconstruction of I-376, the Parkway East, in Pittsburgh, Pennsylvania is made to validate the adequacy of the network assignment model. Results are compared with actual volume counts collected during periods with and without traffic restrictions. The model produced estimates of link volumes that were, on average, from 16% to 28% different from the observed link counts along two screenlines. Large discrepancies with some of the counts could be explained in part by aberrations in the observed data or in the network model's structure. A sketch-planning analysis is also performed, and the results are compared with those from the network assignment model. The network assignment model is also used to predict the impacts of a hypothetical reconstruction scenario in which the Parkway East is totally closed during its reconstruction.