A method for assessing transportation impacts of new land developments using integrated land use and transportation network modeling

The transportation impact of new land developments on the local communities is reflected in an increase of trip-making activities, related increase in vehicular traffic, and expansion of transportation capacity necessary to serve the growing travel demand. To better analyze and understand these impacts, they can be classified in three categories: (1) new traffic flows generated directly by the users of a new development; (2) new traffic flows resulting from indirect developments, i.e., additional developments or growth in the local area related to or serving the needs of initial development; and (3) traffic flows induced by the new or improved transportation facilities, including flows associated with induced land developments. Proper assessment of the transportation impacts of new land development is critical in determining the required improvements in transportation infrastructure and other mitigating strategies, equitable allocation of costs associated with the transportation improvements and mitigating strategies, as well as the appropriate policies that serve the desired local and regional urban development goals. The assessment should, therefore, take into account all three components of transportation impact, i.e., direct, indirect, and induced. The traffic impact assessment methodology developed in dissertation research integrates land use, travel demand, and transportation network modeling to quantify each component of the traffic impact on the highway network providing access to the new land development. The modeling procedure is accomplished in a iterative process over eight modeling phases, and involves a feedback loop between travel demand and network model, and the corresponding land use model for a given geographic region. The methodology calculates incremental VMT associated with each component of the transportation impact, and thus can ascertain corresponding transportation costs if the cost of VMT is known. Using the appropriate formula, each cost component (direct, indirect, and induced) can be allocated to either the local community (to be paid from local taxes and development fees) or the regional traveling public (to be paid from regional transportation funds, such as proceeds from the gas tax). The methodology was demonstrated in a case study of a hypothetical land development in a local community and a corollary highway improvement in a medium sized metropolitan area. A sensitivity analysis was also conducted to evaluate response of the modeling procedure to changes in in key input parameters. The results of the case study reveal that the immediate (short-term) induced traffic impacts are far more significant than the long term impacts, and they increase with the size of the highway capacity expansion. Besides being far less significant than short term impacts, the analysis showed the long-term induced impacts to be consistent regardless of the size of highway capacity expansion, measured as a percent of the overall change in VMT. The case study analysis demonstrated that the methodology can be a useful tool for quantifying direct, indirect, and induced traffic impacts of land development, as well as allocation of responsibilities for underlying transportation system improvements. The elasticities calculated as part of the sensitivity analysis can provide a guide in evaluating expected increase of VMT due to direct, indirect, short- and long-term induced impacts