Repurposing City Streets: Assessing City-Scale Congestion and VMT Impacts with a System Dynamics Scenario Analysis

Abstract

Alternate street uses (ASUs) have been explored worldwide to capitalize upon public space to meet other societal needs. One widely adopted strategy catalyzed by the COVID-19 pandemic is the repurposing of roadway space from vehicular travel to other purposes, such as nonmotorized mobility, commercial use, or as social/recreational space. This thesis presents a scenario analysis of ASU policies using a system dynamics (SD) framework to investigate downstream and interacting effects of ASU policies and allocation in Seattle, WA and Phoenix, AZ. Model calibration was done with the Puget Sound Regional Council 2019 Household Travel Survey and Federal Highway Administration 2017 National Household Travel Survey datasets. It was found that increasing the existing amount of street space repurposed for commercial and social/recreational use led to decreased congestion in both Seattle and Phoenix models, while also increasing the non-motorized transportation (NMT) mode share. In higher-density cities with lower drive mode share like Seattle, increasing lane reallocation for uses that increase the capacity, safety, and reliability of NMT and transit modes can reduce both congestion and VMT. In lower-density cities with higher drive mode share like Phoenix, repurposing more street space for NMT would lower VMT; repurposing street space for transit use, however, yields little meaningful benefit. These findings support policies promoting widespread ASU placement and concerns about generating increased congestion by removing travel lanes are refuted. The thesis concludes that at least in higher-density cities, the reallocation of street space is not a zero-sum game, as those who still choose to drive experience reduced congestion, and the non-drivers receive safety and capacity enhancements. Furthermore, reduced total VMT supports broader traffic safety and emissions reduction goals.