Evaluation Considerations and Geometric Nuances of Reduced Conflict U-Turn Intersections (RCUTs) 26 th Annual Transportation Research Conference Saint Paul RiverCentre May 20, 2015
Presentation Outline Introduction to RCUTs Evaluation Considerations Case Study Geometric and Capacity Nuances Lessons Learned
Introduction to RCUTs
How are Conflicts Reduced? J-Turn RCUT Minor street thru and left-turns are restricted and re-routed Left turns from major roadway may also be restricted and re-routed
Example: Hwy 65 at 169 th Ave NE, Ham Lake, MN Hwy 65 169 th Ave NE
Divided Highway Intersections Cause Driver Decision Overload
Evaluation Considerations
Critical Issues with Respect to Safety and Operations Location of downstream U-Turn movement is critical to minimizing right-turn to U-Turn weaving impacts, mainline traffic operations (i.e., lane changing and speed reductions), and, impacts to adjacent low volume driveways along a corridor. Movement control (e.g., signal control, stop control, yield control, or free condition) for minor approach right-turn movements is critical to minimizing impacts to mainline weaving. Higher than average truck volumes may require longer gaps in mainline traffic to accommodate the U-Turn movement.
Traffic Evaluation Measures of Effectiveness (MOEs) Network: Corridor: Intersections: Weave Areas: Delay, Travel Time, Speed Travel Times Delay, Queuing Speeds*, Lane Changes * by vehicle class
Case Study
STH 54 at CTH U, Wood County/Portage County, WI CTH U 84th St. N Future 72nd Street Connection STH 54 64th St. 72nd St. 65 mph Posted Speed 5.5% Heavy Trucks
Case Study Need? Existing crash problem: High number of angle crashes at CTH U High number of single vehicle crashes along the corridor Future development: Business park and residential development north of STH 54 between 64th Street and CTH U
Case Study Need? Poor levels operations under future Year 2035 partial and full build out development scenarios The potential dangerous conflicts that currently exist and the lack of gaps and associated storage issues that occur when larger vehicles perform two-stage crossing movements.
Alternative A Three Restricted Crossovers with downstream U-Turns CTH U 84th St. 750 ft. 1150 ft. 1400 ft. STH 54 800 ft. 2500 ft. 1450 ft. 1200 ft. Scale = 2640 ft. N 64th St. 72nd St. Note: All median openings between the western U-Turn and eastern U-Turn, except at the Restricted Crossovers and U-Turn Crossovers, will be closed. This includes 84th Street.
Alternative B Two Restricted Crossovers with Two downstream U-Turns per direction CTH U 84th St. 750 ft. 900 ft. STH 54 800 ft. 2500 ft. 1000 ft. Scale = 2640 ft. N 64th St. 72nd St. Note: All median openings between the western U-Turn and eastern U-Turn, except at the Restricted Crossovers and U-Turn Crossovers, will be closed. This includes 84th Street and 72nd Street.
Alternative C Three Restricted Crossovers with U-turns plus WB U-Turn at West End CTH U 84th St. STH 54 800 ft. Scale = 2640 ft. N 64th St. 72nd St. Note: All median openings between the western U-Turn and eastern U-Turn, except at the Restricted Crossovers and U-Turn Crossovers, will be closed. This includes 84th Street.
Alternative D Two Restricted Crossovers with U-turns plus WB U-Turn at West End and EB U-Turn at East End CTH U 84th St. 750 ft. 900 ft. STH 54 800 ft. 2500 ft. 1000 ft. Scale = 2640 ft. N 64th St. 72nd St. Note: All median openings between the western U-Turn and eastern U-Turn, except at the Restricted Crossovers and U-Turn Crossovers, will be closed. This includes 84th Street and 72nd Street.
Sample Results: Lane-by-Lane Speed Evaluation
Sample Results: Travel Time Comparison
Evaluation Summary Network Performance Alternatives B and D: Network latent demand Highest overall travel times Lowest average speeds Alternative A: Lowest total travel time Highest average speed Alternative C: Lowest average delay Isolated Locations Alternatives B and D: U-turn between 64th Street and 72nd Street cannot accommodate volume Long queues on southbound 72nd Street Alternative A: U-turn between 72nd Street and CTH U operating at LOS F Alternative C: U-turn at 72nd Street operating at LOS D
Can Alternative A be Improved? Provide signal at U-Turn that would only operate during peak hours? Adds signal to unsignalized corridor Provide inside acceleration lane? Extends into downstream left-turn lane Creates left-lane merge Would impact large trucks Re-design to use Wide Loon? Revised Alternative A!
U-turn Crossover (Wide Loon ) Wide Loon to accommodate U-Turn path Revised Alternative A!
Geometric and Capacity Nuances
What Geometric and Capacity Nuances Should be Considered? Turn lanes: Provide adequate length right-turn and left-turn lanes from mainline Critical gap and turning speeds: Impacts intersection LOS Wide vs. Narrow Loons : Impacts intersection LOS Impacts mainline speeds
What Geometric and Capacity Nuances Should be Considered? Left-turn from major street: HCM 2000 Exhibit 17-5 (four-lane major street) HCM 2010 Exhibit 19-10 4.1 seconds U-Turn from major street to major street: 6.4 to 6.9 seconds HCM 2010 Exhibit 19-10 6.4 seconds (wide median) and 6.9 seconds (narrow median) The Gap Acceptance Study of U-turn at Median Openings by Yang et al. (2001 ITE Annual Meeting) Literature referenced on ITE, TRB, and FHWA websites U-Turn gap acceptance ranges between 5.8 and 7.4 seconds, with an average of 6.7 seconds
Restricted Crossover Option: Control right-turn with island and yield Critical Gap = 4.1s Turn Speed = 15 mph
Back-to-Back U-Turn Crossover (Narrow Loon ) Narrow Loon to accommodate U-Turn path Critical Gap = 6.9s Turn Speed = 9 mph
Restricted Crossover with U-Turns (Wide Loon ) Critical Gap = 4.1s/6.4s Turn Speed = 15 mph Partial roundabout to accommodate U-Turns
U-Turn Crossover (Wide Loon ) Wide Loon to accommodate truck U-Turn path Critical Gap = 6.4s Turn Speed = 15 mph
Narrow Loon 1: U-Turn Vehicle Accepts Gap Narrow vs. Wide Loons Wide Loon 1: U-Turn Vehicle Accepts Gap 2: U-Turn Vehicle Clears Left Lane 2: U-Turn Vehicle Clears Left Lane Time in Left Lane = 5.3 secs Time in Left Lane = 2.2 secs
Narrow Loon 1: U-Turn Truck Accepts Gap Narrow vs. Wide Loons 1: U-Turn Wide Truck Loon Accepts Gap 2: U-Turn Truck Clears Left Lane 2: U-Turn Truck Clears Left Lane Time in Left Lane = 7.5 secs Time in Left Lane = 5.5 secs
Updated Evaluation Summary Performance Measure Currently in Design! Alternative A Revised Alternative C Network Performance Lower Travel Times Higher Average Delays Higher Travel Times Lower Average Delays Operations and LOS Comparable Operations Comparable Operations Mainline Speeds Comparable Speeds for Cars and Trucks Comparable Speeds for Cars and Trucks Travel Time Lower Travel Times Higher Travel Times
Lessons Learned
Lessons Learned RCUTs are viable alternatives to improving safety and operations on divided roadways. RCUTs are not a one size fits all improvement. Need to consider overall corridor perspective when considering RCUTs. Use traffic simulation tools to understand geometric and capacity nuances of the design. Traffic Engineers and Designers need to work closely to understand how design decisions can impact future safety and performance.
Thank You! Leif Garnass, PE, PTOE Project Manager Traffic Studies SRF Consulting Group, Inc. (763) 452-4725 lgarnass@srfconsulting.com