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Alternative Intersections Comparative Analysis

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Alternative Intersections Comparative Analysis Alternative Intersections Comparative Analysis Morgan State University The Pennsylvania State University University of Maryland University of Virginia Virginia Polytechnic Institute & State University West Virginia University The Pennsylvania State University The Thomas D. Larson Pennsylvania Transportation Institute Transportation Research Building University Park, PA 16802-4710 Phone: 814-865-1891 Fax: 814-863-3707 www.mautc.psu.edu OPERATIONAL ANALYSIS OF ALTERNATIVE INTERSECTIONS By: John Sangster and Hesham Rakha Mid-Atlantic University Transportation Center Final Report Department of Civil and Environment Engineering Virginia Polytechnic Institute and State University July 23, 2015 1 1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No. VT-2012-03 4. Title and Subtitle 5. Report Date Operational Analysis of Alternative Intersections July 21, 2015 6. Performing Organization Code Virginia Tech 7. Author(s) 8. Performing Organization Report No. John Sangster and Hesham Rakha 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Virginia Tech Transportation Institute 3500 Transportation Research Plaza 11. Contract or Grant No. Blacksburg, VA 24061 DTRT12-G-UTC03 12. Sponsoring Agency Name and Address 13. Type of Report US Department of Transportation Final Report Research & Innovative Technology Admin UTC Program, RDT-30 14. Sponsoring Agency Code 1200 New Jersey Ave., SE Washington, DC 20590 15. Supplementary Notes 16. Abstract Alternative intersections and interchanges, such as the diverging diamond interchange (DDI), the restricted crossing u-turn (RCUT), and the displaced left-turn intersection (DLT), have the potential to both improve safety and reduce delay. However, partially due to lingering questions about analysis methods and service measures for these designs, their rate of implementation remains low. This research attempts to answer three key questions. Can alternative intersections and interchanges be incorporated into the existing level of service and service measure schema, or is a new service measure with an updated level of service model required? Is the behavior of drivers at alternative intersections fundamentally similar to those at conventional intersections, such that traffic microsimulation applications can accurately model the behaviors observed in the field? Finally, is the planning level tool made available through FHWA an accurate predictor of the relative performance of various alternatives, or is an updated tool necessary? Discussion and case study analysis are used to explore the existing level of service and service measure schema. The existing control delay measure is recommended to be replaced with a proposed junction delay measure that incorporates geometric delay, with the existing level of service schema based on control type recommended to be replaced by a proposed schema using demand volume. A case study validation of micro- and macroscopic analysis methods is conducted, finding the two microscopic methods investigated to match field observed vehicle delays within 3 to 7 seconds for all designs tested, and macroscopic HCM method matching within 3 seconds for the DDI, 35 seconds for the RCUT, and 130 seconds for the DLT design. Taking the critical lane analysis method to be a valid measure of operations, the demand-volume limitations of each alternative design is explored using eighteen geometric configurations and approximately three thousand volume scenarios, with the DLT design predicted to accommodate the highest demand volumes before failure is reached. Finally, six geometries are examined using both the planning-level tool and the validated microsimulation tool, finding that the curve of the capacity-to-delay relationship varies for each alternative design, invalidating the use of critical lane analysis as a comparative tool. 17. Key Words 18. Distribution Statement Alternative intersections, capacity, delay, level of service 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price 130 2 ABSTRACT Alternative intersections and interchanges, such as the diverging diamond interchange (DDI), the restricted crossing u-turn (RCUT), and the displaced left-turn intersection (DLT), have the potential to both improve safety and reduce delay. However, partially due to lingering questions about analysis methods and service measures for these designs, their rate of implementation remains low. This research attempts to answer three key questions. Can alternative intersections and interchanges be incorporated into the existing level of service and service measure schema, or is a new service measure with an updated level of service model required? Is the behavior of drivers at alternative intersections fundamentally similar to those at conventional intersections, such that traffic microsimulation applications can accurately model the behaviors observed in the field? Finally, is the planning level tool made available through FHWA an accurate predictor of the relative performance of various alternatives, or is an updated tool necessary? Discussion and case study analysis are used to explore the existing level of service and service measure schema. The existing control delay measure is recommended to be replaced with a proposed junction delay measure that incorporates geometric delay, with the existing level of service schema based on control type recommended to be replaced by a proposed schema using demand volume. A case study validation of micro- and macroscopic analysis methods is conducted, finding the two microscopic methods investigated to match field observed vehicle delays within 3 to 7 seconds for all designs tested, and macroscopic HCM method matching within 3 seconds for the DDI, 35 seconds for the RCUT, and 130 seconds for the DLT design. Taking the critical lane analysis method to be a valid measure of operations, the demand-volume limitations of each alternative design is explored using eighteen geometric configurations and approximately three thousand volume scenarios, with the DLT design predicted to accommodate the highest demand volumes before failure is reached. Finally, six geometries are examined using both the planning-level tool and the validated microsimulation tool, finding that the curve of the capacity-to-delay relationship varies for each alternative design, invalidating the use of critical lane analysis as a comparative tool. 3 CHAPTER 1. INTRODUCTION 1.1 Background and Motivation The principal arterial system amounts to less than 10 percent of US street system mileage, but accounts for nearly one-half of all vehicle-miles travelled [1]. As nationwide congestion continues to increase, the arterials bear much of the brunt, with ever increasing delays and limited opportunities for increasing capacity. These roadways serve an important purpose in our transportation network by balancing access with mobility. Though the need exists to increase their capacity, their purpose remains balanced and converting them to freeways is not a valid solution. With arterial corridors in failure, it is often the case that the single greatest limiting factor for capacity are signalized intersections with multiple left turn phases, which fail to accommodate high through-put volumes while also accommodating turning movement and side-street flows. The addition of lanes to increase capacity is insufficient to solve the problem of limited green- time percentage for through traffic. Additional lanes can often exacerbate existing problems, as intersection size expands both lost time and minimum pedestrian phase lengths. Alternative intersections seek to address these capacity issues by segregating or diverting turning movements, which concurrently reduces and separates the number of conflict points. Some professionals object to alternative solutions due to a perceived increase in cost, but when a high cost intersection improvement can postpone the need to add additional lanes along a corridor or prevent the construction of an interchange, the cost savings of alternative intersections become apparent. Due to the potential for increased safety, congestion reduction, and cost savings, the Federal Highway Administration (FHWA) has recently been an advocate for what they refer to as “novel” intersection designs [2]. Even with the backing of the Federal Government, these designs remain fringe solutions, as problems with driver expectancy continue to be a legitimate concern. While public information campaigns in advance of implementation can assist local drivers, a certain percentage of all traffic will be new to an area. Convincing an agency responsible for any potential alternative intersection that the anticipated benefits outweigh the unknown liabilities often involves providing multiple existing examples with observed data. The logical fallacy of circular cause and consequence has prevented these unique designs from being put into practice, with designs failing to be implemented on the basis of them having not already been built elsewhere. 1.1.1 Overview of Alternative Intersections The category of intersection design known as alternative intersections was known as unconventional intersections only five years ago, and five years from now may be so commonplace as to no longer hold the title alternative. These designs have come a long way since the first proposal of what is now called the restricted crossing u-turn design in the late 80’s [3]. The near-universal adoption of the modern roundabout as a successful alternative
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