Evaluation of Operation and Accuracy of Available Smart Growth Trip Generation Methodologies for Use in California

Abstract

It is well known that a standard application of the ITE trip rates for an area with many smart growth characteristics will result in an over-estimation of the number of trips generated. No commonly agreed on methodology in the United States for estimating trip generation takes into account the smart growth characteristics of a land use development project. Several methods have been recently proposed as incremental advancements toward developing such a methodology. This paper identifies eight available methodologies, five of which are appropriate for use in California. The five candidate methods are compared with the traditional ITE trip generation method in a two-part assessment. The first part involves evaluating the methods against a variety of operational criteria developed through discussions with a panel of transportation practitioners. The second part involves testing the accuracy of the methods by comparing the predictions of the various methods against available traffic counts and other data at 22 California sites that contain at least some characteristics of smart growth. On the basis of the evaluation, the authors conclude that all five methods have advantages and disadvantages and that while no single method emerged as the best for use in smart growth development projects, all methods appear to be more accurate at predicting the number of trips generated than standard application of the ITE base rates. Furthermore, this analysis focuses on candidate methods deemed appropriate for use in California, but this research has value and potential implications for smart growth transportation planning efforts outside California.

Method to adjust Institute of Transportation Engineers vehicle trip-generation estimates in smart-growth areas

“…This would include comparing the trip-generation estimates from each method to ground-truth counts and evaluating ease of use for practitioners, for example, using the method employed by Shafizadeh et al (2012). These comparisons could eventually suggest refinements to improve each individual method or lead to a combined method with greater predictive power.…”

“…However, since the trip-generation contexts are different in these countries (e.g., different transportation facility design guidelines, transportation costs, and cultures), they are not likely to be applicable in the United States. Additional details about alternative trip-generation methods are summarized by Shafizadeh et al (2012) and Clifton et al (2012a).…”

“…While each of the methods has advanced the state-of-the-practice, this evaluation identified practical limitations to using each of the methods. Shafizadeh et al (2012) also used motor vehicle count and intercept survey data from 22 California sites to evaluate the predictive accuracy of each of these alternative approaches. None of the alternative methods provided results that were consistently more accurate than any of the other test methods, but all of these methods still performed better than the existing ITE method.…”

“…All of these tools have the potential to perform better than the suburban-based ITE Trip Generation method for predicting vehicle trip generation in smart-growth areas. Shafizadeh, et al (2012) evaluated the operational characteristics and accuracy of the first five methods listed above (the San Francisco and New York methods were not considered to have broad applicability outside of these cities). Operational characteristics were evaluated by a panel of experts, according to criteria in the following categories: 1) ease of use, 2) sensitivity to key smart-growth elements, 3) input requirements, 4) output features, and 5) usability of the approach in helping to define smart-growth projects based on their performance.…”

Using household travel surveys to adjust ITE trip generation rates

“…While the ITE is currently in the process of updating the method for data collection and estimation of traffic, the new extensive, nationally collected, multi-modal, personoriented data will not likely be available for some time. Meanwhile, local governments continue to be hampered by methods of estimating transportation impact that are simply not sensitive to urban environments , Nelson\Nygaard Consulting Associates 2005, Rizavi and Yeung 2010, Shafizadeh et al 2012.…”