Travel demand forecast for an urban network using the System II Regional Information System and Subarea Analysis Software

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Virginia Tech


By the year 2010, more than 40 percent of the city of Alexandria’s population will be housed within the Beauregard street corridor. The corridor will thus experience severe traffic congestion by the design year. A significant portion of the traffic volumes on the Beauregard street do not belong to the corridor, but are diverted to the other major neighboring roadways - in particular the Shirley Memorial Highway (I-395). The existing capacity of the study corridor will not be able to handle the future traffic volumes. Hence this study was conducted at the request of the city council of Alexandria.

This report documents the first phase of a two phase study. The objective of the first phase of this study, which is the basis for this project report, mainly consists of travel demand forecasting for the Beauregard street corridor for the design year, 2010. The process thus included calibration of the model to enable simulation of travel demand in the Beauregard street corridor.

One of the major drawbacks of this study is the fact that transit was excluded from consideration. Also, in the FOCUS option of the study, only three out of the available five levels of network and zonal data were used. As a result, the extracted data provided a very coarse network (major highway elements only) and aggregate zonal systems outside the study corridor. This is one of the main reasons for the calibration not being accurate outside the Beauregard street study corridor. However, within the study corridor, a detailed network (including local streets) and zonal attributes were retained which helped in accurate calibration of the study corridor. For a better calibration of the region outside the study corridor, it is suggested that all the five levels of network and zonal details be used in the FOCUS option. But the main objective of this study is to forecast travel demand for the study corridor with a reasonable degree of accuracy, which has been achieved.

The SYSTEM II travel demand forecasting model is based on the principles of the gravity model which assumes that the impedance function to travel behavior remains unchanged from the base year to the design year. This static behavior of the gravity model leaves ample room for criticism and thus, further research. However, no concrete evidence 1s available to prove inappropriateness of this model’s use in traditional transportation planning.

The peak hour factors developed from the previous works of JHK & associates: Capital beltway and Route 28 studies were then applied to obtain the AM peak hour travel tables. These AM peak hour travel table were then assigned to the network to obtain AM peak hour traffic volumes. The AM peak hour volumes thus obtained will be used to recommend strategies for the alleviation of traffic congestion in the Beauregard street corridor. One of the many recommendations currently under study, involves the construction of a diamond-point grade separated interchange configuration at the intersection of Beauregard street with Seminary road and with King street (route 7). Further investigation needs to be carried out regarding the feasibility of other such strategies for the alleviation of traffic congestion in the Beauregard street corridor.