The Effects of Connectivity and Automation on Saturation Headway and Capacity at Signalized Intersections

TL;DR

This study evaluates how connected and automated vehicles influence saturation headway and capacity at signalized intersections, showing that higher CAV penetration improves capacity while higher AV penetration can worsen traffic flow.

Contribution

It introduces a simulation framework to analyze mixed traffic scenarios with HVs, CVs, AVs, and CAVs, revealing their impacts on intersection capacity and saturation headway.

Findings

Increasing CAV market share boosts capacity by up to 80%.

Higher AV penetration can decrease intersection capacity by 20%.

Connected vehicles improve traffic flow by reducing stops and delays.

Abstract

This paper analyzes the potential effects of connected and automated vehicles on saturation headway and capacity at signalized intersections. A signalized intersection is created in Vissim as a testbed, where four vehicle types are modeled and tested: (I) human-driven vehicles (HVs), (II) connected vehicles (CVs), (III) automated vehicles (AVs), and (IV) connected automated vehicles (CAVs). Various scenarios are defined based on different market penetration rates of these four vehicle types. AVs are assumed to move more cautiously compared to human drivers. CVs and CAVs are supposed to receive information about the future state of traffic lights and adjust their speeds to avoid stopping at the intersection. As a result, their movements are expected to be smoother with a lower number of stops. The effects of these vehicle types in mixed traffic are investigated in terms of saturation headway, capacity, travel time, delay, and queue length in different lane groups of an intersection. A Python script code developed by Vissim is used to provide the communication between the signal controller and CVs and CAVs to adjust their speeds accordingly. The results show that increasing CV and CAV market penetration rate reduces saturation headway and consequently increases capacity at signalized intersections. On the other hand, increasing the AV market penetration rate deteriorates traffic operations. Results also indicate that the highest increase (80%) and decrease (20%) in lane group capacity are observed, respectively, in a traffic stream of 100% CAVs and 100% AVs.