Design Features of Activity-Based Models in Practice

This paper describes design features of several different regional activity-based models (ABMs) that share the coordinated travel–regional activity modeling platform (CT-RAMP) design and software platform. The CT-RAMP models are characterized by features such as a full simulation of travel decisions for discrete households and persons, explicit tracking of time in half-hourly increments, the use of time constraints on the generation of travel, and explicitly modeled intrahousehold interactions across a range of activity and travel dimensions. These important features allow for greater behavioral realism in representing the response to numerous transportation policies. Each implementation of the CT-RAMP system, as for many ABM systems used in practice over the years, shares certain common features with others. However, each implementation is tailored to address specific regional conditions and includes additional advanced features to provide increased policy sensitivity and greater behavioral realism. These features are explained in the paper and analyzed in the context of model applications for different transportation projects and policies. Some of these features stem from ongoing intensive research and development in the field, including cross-pollination of ideas between the CT-RAMP family and other ABMs developed elsewhere, but many other features are unique and were driven by practical needs. The main conclusion of this paper is that it is too early to establish a completely generic and standard approach to an ABM design in practice. The evolution of features in ABMs still continues and is driven by theoretical achievements in behavior research and practical considerations.