Evaluation Of IDAS: A Determination of the Validity of the ITS Development Analysis System
Creators: name: Xenelis, Nancy
Publisher: name: The University of North Carolina at Chapel Hill University Libraries
Year: 2005
Subjects: Intelligent Transportation Systems

description: With urban transportation systems becoming increasingly congested, the deployment of Intelligent Transportation Systems (ITS) allows for a decrease in congestion without necessarily adding additional capacity to the transportation network. Intelligent Transportation Systems can best be defined as advanced technologies which are used to improve the efficiency and safety of our Nation's surface transportation system, including highways, transit and rail1. In order to better integrate ITS applications into the transportation planning system, IDAS was developed as a sketch-level ITS analysis software. Developed by Cambridge Systematics for the Federal Highway Administration, IDAS works as a post-processor to the travel demand model to estimate the impacts of ITS. The purpose of this project was to determine if IDAS is a valid planning tool. This was accomplished through a detailed literature review synthesizing the experiences and opinions of practitioners who have used IDAS. This study is intended to inform policy makers and practitioners about the issues involved with incorporating IDAS into the transportation planning system. This study focused on the empirical validity of IDAS. Empirical validity, in terms of IDAS, can best be defined as the ability of IDAS to accurately predict the measured real-world systems operational behavior2. It was found that the ability of IDAS to accurately estimate the impacts of ITS deployments depends on the quality of the travel demand model and modified default values. The validity of IDAS is also dependent on the type of ITS deployment analyzed, and the degree to which the user understands the shortcomings of IDAS. Three issues emerged to put into question IDAS's empirical validity. First, the set-up is cumbersome and time consuming which led to errors in the input data; second, there are a number of questionable default values; and third, IDAS only models transit deployments system-wide, which has a great potential to lead to inaccurate results. The table below summarizes the findings of the literature review. The table outlines the ITS deployment analyzed, the determined validity of IDAS, and the reasons for that determination. Electronic Transit Fare Collection is listed as "Questionable" because although IDAS was reported as beneficial for analyzing this deployment, there were several issues reported which puts into question the validity. This study also presents opportunities for future research. No literature was found which compared the impacts of real-world ITS deployments against impacts generated by IDAS. Although time consuming and expensive, a more detailed, mathematical approach would be beneficial in determining the empirical validity of IDAS as a planning tool. The question of IDAS's conceptual validity also remains. Conceptual validity pertains to the theoretical foundations of the software. Determining the conceptual validity would require comparing the most current research findings with the assumptions used by IDAS. This would also prove to be a time-consuming exercise, but would be invaluable to current and future IDAS users. It would also provide IDAS developers with information critical to improving the validity of the software.