arXiv subjects

Joan L. Walker

Publications and source records attributed to Joan L. Walker.

5 recordsLinked to original sources

arXiv2025

Beyond Centrality: Understanding Urban Street Network Typologies Through Intersection Patterns

The structure of road networks plays a pivotal role in shaping transportation dynamics. It also provides insights into how drivers experience city streets and helps uncover each urban environment's unique characteristics and challenges. Consequently, characterizing cities based on their road network patterns can facilitate the identification of similarities and differences, informing collaborative traffic management strategies, particularly at a regional scale. While previous studies have investigated global network patterns for cities, they have often overlooked detailed characterizations within a single large urban region. Additionally, most existing research uses metrics like degree, centrality, orientation, etc., and misses the nuances of street networks at the intersection level, specifically the geometric angles formed by links at intersections, which could offer a more refined feature for characterization. To address these gaps, this study examines over 100 cities in the San Francisco Bay Area. We introduce a novel metric for classifying intersections, distinguishing between different types of 3-way and 4-way intersections based on the angles formed at the intersections. Through the application of clustering algorithms in machine learning, we have identified three distinct typologies - grid, orthogonal, and organic cities - within the San Francisco Bay Area. We demonstrate the effectiveness of the metric in capturing the differences between cities based on street and intersection patterns. The typologies generated in this study could offer valuable support for city planners and policymakers in crafting a range of practical strategies tailored to the complexities of each city's road network, covering aspects such as evacuation plans, traffic signage placements, and traffic signal control.

cs.SI↗

arXiv2024

Share, Collaborate, Benchmark: Advancing Travel Demand Research through rigorous open-source collaboration

This research foregrounds general practices in travel demand research, emphasizing the need to change our ways. A critical barrier preventing travel demand literature from effectively informing policy is the volume of publications without clear, consolidated benchmarks, making it difficult for researchers and policymakers to gather insights and use models to guide decision-making. By emphasizing reproducibility and open collaboration, we aim to enhance the reliability and policy relevance of travel demand research. We present a collaborative infrastructure for transit demand prediction models, focusing on their performance during highly dynamic conditions like the COVID-19 pandemic. Drawing from over 300 published papers, we develop an open-source infrastructure with five common methodologies and assess their performance under stable and dynamic conditions. We found that the prediction error for the LSTM deep learning approach stabilized at a mean arctangent absolute percentage error (MAAPE) of about 0.12 within 1.5 months, whereas other models continued to exhibit higher error rates even a year into the pandemic. If research practices had prioritized reproducibility before the COVID-19 pandemic, transit agencies would have had clearer guidance on the best forecasting methods and quickly identified those best suited for pandemic conditions to inform operations in response to changes in transit demand. The aim of this open-source codebase is to lower the barrier for other researchers to replicate, reproduce models and build upon findings. We encourage researchers to test their own modeling approaches on this benchmarking platform, challenge the analyses conducted in this paper, and develop model specifications that can outperform those evaluated here. Further, collaborative research approaches must be expanded across travel demand modeling if we wish to impact policy and planning.

cs.LG↗

arXiv2021

Socially-Aware Evaluation Framework for Transportation

Technological advancements are rapidly changing traffic management in cities. Massive adoption of mobile devices and cloud-based applications have created new mechanisms for urban traffic control and management. Specifically, navigation applications have impacted cities in multiple ways by rerouting traffic on their streets. As different routing strategies distribute traffic differently across the city network, understanding these differences across multiple dimensions is highly relevant for policymakers. In this paper, we develop a holistic framework of indicators, called Socially-Aware Evaluation Framework for Transportation (SAEF), that will assist in understanding how traffic routing and the resultant traffic dynamics impact city metrics, with the intent of avoiding unintended consequences and adhering to city objectives. SAEF is a holistic decision framework formed as an assembled set of city performance indicators grounded in the literature. The selected indicators can be evaluated for cities of various sizes and at the urban scale. The SAEF framework is presented for four Bay Area cities, for which we compare three different routing strategies. Our intent with this work is to provide an evaluation framework that enables reflection on the consequence of policies, traffic management strategies and network changes. With an ability to model out proposed traffic management strategies, the policymaker can consider the trade-offs and potential unintended consequences.

eess.SY↗

arXiv2018

Asymmetric, Closed-Form, Finite-Parameter Models of Multinomial Choice

In transportation, the number of observations associated with one discrete outcome is often greatly different from the number of observations associated with another discrete outcome. This situation is known as class-imbalance. In statistics, one hypothesized explanation for class imbalance is the existence of data generating processes that are characterized by asymmetric (as opposed to typically symmetric) probability functions. Despite being a valid hypothesis for class-imbalanced choice situations, few simple models exist for testing this explanation in transportation settings---settings that are inherently multinomial. Our paper fills this gap. As such, it should be of interest to transportation scholars and practitioners alike. Overall, we addressed the following questions: "how can one construct asymmetric, closed-form, finite-parameter models of multinomial choice" and "how do such models compare against commonly used symmetric models?" To do so, we (1) introduced a new class of closed-form, finite-parameter, multinomial choice models that we call "logit-type models," (2) introduced a procedure for using our logit-type models to extend existing binary choice models to the multinomial setting, and (3) introduced a procedure for creating new binary choice models (both symmetric and asymmetric). Together, our contributions allow us to create new asymmetric, multinomial choice models by creating multinomial extensions of asymmetric, binary choice models that already exist or that we create ourselves. We demonstrated our methods by developing four new asymmetric, multinomial choice models. We found that most of our asymmetric models dominated the multinomial logit (MNL) model in terms of in-sample and out-of-sample log-likelihoods. Moreover, on our two empirical applications, we also found practical differences between the MNL model and our new asymmetric models.

stat.AP↗

arXiv2017

Machine Learning Meets Microeconomics: The Case of Decision Trees and Discrete Choice

We provide a microeconomic framework for decision trees: a popular machine learning method. Specifically, we show how decision trees represent a non-compensatory decision protocol known as disjunctions-of-conjunctions and how this protocol generalizes many of the non-compensatory rules used in the discrete choice literature so far. Additionally, we show how existing decision tree variants address many economic concerns that choice modelers might have. Beyond theoretical interpretations, we contribute to the existing literature of two-stage, semi-compensatory modeling and to the existing decision tree literature. In particular, we formulate the first bayesian model tree, thereby allowing for uncertainty in the estimated non-compensatory rules as well as for context-dependent preference heterogeneity in one's second-stage choice model. Using an application of bicycle mode choice in the San Francisco Bay Area, we estimate our bayesian model tree, and we find that it is over 1,000 times more likely to be closer to the true data-generating process than a multinomial logit model (MNL). Qualitatively, our bayesian model tree automatically finds the effect of bicycle infrastructure investment to be moderated by travel distance, socio-demographics and topography, and our model identifies diminishing returns from bike lane investments. These qualitative differences lead to bayesian model tree forecasts that directly align with the observed bicycle mode shares in regions with abundant bicycle infrastructure such as Davis, CA and the Netherlands. In comparison, MNL's forecasts are overly optimistic.

stat.AP↗