Urban Traffic Network Operations: Roundabouts vs. Signalized Intersections
Open Access
- Author:
- Taglieri, David
- Graduate Program:
- Civil Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- February 28, 2022
- Committee Members:
- Patrick Fox, Program Head/Chair
Vikash V. Gayah, Thesis Advisor/Co-Advisor
Eric T. Donnell, Committee Member
S. Ilgin Guler, Committee Member - Keywords:
- traffic
traffic control
roundabout
roundabouts
macroscopic fundamental diagram
network exit function
transportation
engineering
MFD
NEF - Abstract:
- Roadway intersections are a critical component in urban traffic networks. The conflicting traffic flows are the cause of many vehicular crashes. Separating these conflicting movements typically involves stopping one or more movement to allow another one to go, which creates regular bottlenecks in traffic. Modern roundabouts are a circular intersection type that has been called a “Proven Safety Countermeasure” by the Federal Highway Administration and has been shown to reduce traffic delays at individual intersections over prior alternatives since vehicles do not have to stop. However, their performance when installed on an entire network is unknown. Recently, novel methods have been developed that can be used to describe traffic states aggregated across an entire network, allowing network-level performance to be more easily measured and compared. These tools can be used to compare networks which are identical in nature with one parameter varied. Previous work in this field has evaluated the operational performance of one-way and two-way networks, banning left turns at signals, and developed an optimal control strategy for signalized two-way networks based on traffic states. This study extends the field of research to include network performance when roundabouts are applied at intersections, which had been previously discounted despite its safety benefits. Comparing networks with a roundabout at each intersection to identical networks with signal control at each intersection yielded positive and negative conclusions for the roundabouts’ performance when deployed network-wide. At uncongested states, roundabout-controlled networks outperformed the signalized networks significantly. However, the roundabouts peaked at lower traffic densities than the signals, and performance sharply dropped off as congestion was present. In two-lane networks, the roundabout networks had higher trip completion potential than signalized networks for all but the largest configuration. There was a significant decrease in the roundabouts’ performance when adding a lane in each direction of travel, although the roundabouts still displayed higher productivity at uncongested states. The software also measured the vehicular fuel consumption and emissions. Roundabout-controlled networks consumed more fuel per trip than signalized networks, which disputes prior studies on roundabouts and fuel performance, but this may have been a product of the model used in the simulation. This study expands a relatively new field of literature to include the roundabout with several conclusions. Roundabouts should be considered by city planners as the primary intersection control as right-of-way allows. Additionally, networks that rarely experience major congestion should consider the roundabout as well. Banning left turns in network increases flows within networks, but the increased mobility does not account for the decreased mobility within these networks until the average trip length increases significantly. Lastly, this field of research should expand to include multi-modal traffic configurations as well as determining the viability of the mini-roundabout on a network-wide basis.