This page provides an overview of the key documents detailing the modeling procedures and foundational relationships used in the accessibility-based sketch model. The documents are ordered in a way that roughly matches the model application steps. A brief description of each document is provided below.
Decay rates in accessibility summarization: Decay refers to the concept that travel is less likely to occur between two zones if the cost to travel between them is high. Specific rates of decay vary by mode and travel purpose. This page provides the details of the data and model fitting techniques used to define decay rates for accessibility summarization and trip distribution in the West Station analysis.
Trip generation
Trip generation rates: This page provides a basic overview of the trip generation process, including a rundown of trip generation rates and the procedures used to cross-classify households for trip generation purposes.
Literature review: Trip generation and the build environment: This is a brief review of academic and industry literature assessing how different characteristics of the built environment influence trip generation rates. The literature is ambivalent about the role of accessibility and related measures in altering person trip generation rates. Rather, accessibility has a more pronounced influence on mode choice. For this reason, the West Station analysis does not use accessibility scores to alter trip generation rates, focusing instead on mode choice and trip distribution applications.
Mode Choice
Overview of model sensitivities: This page offers a high-level summary of the factors that influence travel behavior outputs generated by the accessibility-based mode, focusing on the factors and parameters that influence accessibility scores and mode choice model results.
Mode choice model detailed report: This report presents the details of the mode choice modeling conducted for the Boston region to develop behavioral relationships based on accessibility scores and demographic data.
Trip distribution
K factors: This page describes adjustments made to raw outputs from the accessibility-based mode choice models prior to distribution to generate mode share estimates that better approximate those generated by the regional travel demand model. This adjustment helps maintain consistency in trip-making expectations established by these two different modeling frameworks.
Potential future enhancement - Trip survival curves: This report describes an approach to enrich the trip distribution process using survival (or proportional hazards) modeling techniques. The modeling framework was developed as part of the West Station analysis but not deployed due to time and computational constraints. The potential benefits of this enhancement to the decay curves used in the trip distribution step include more nuanced responses to travel opportunities based on cost parameters and household characteristics beyond what can be obtained using the generalized cost constructs used in the pilot project application.
TNC Trips: This report describes the data and methods used in developing estimates of TNC trip-making based on the sketch model trip table outputs. The approach focuses on assessing which OD pairs are likely to have trips (by a given mode and for a given travel purpose) replaced by TNC trips based on relative generalized cost distributions for the observed mode and the potential TNC trip.