Area III/IV Conference Educator & Student Participation Program Ames, Iowa 4/11/2006 Potential Rural Expressway Intersection Safety Treatments Research Conducted in Coordination with NCHRP 15-30, “Median Intersection Design for Rural High-Speed Divided Highways” Presented by: Joshua L. Hochstein Ph.D. Candidate Iowa State University (515) 294-7188 firstname.lastname@example.org Iowa State University’s Center for Transportation Research and Education (CTRE) administers the following programs: Bridge Engineering Center • Center for Portland Cement Concrete Pavement Technology • Construction Management & Technology • Iowa Local Technical Assistance Program • Iowa Statewide Urban Design and Specifications• Iowa Traffic Safety Data Service • Midwest Transportation Consortium • Partnership for Geotechnical Advancement • Roadway Infrastructure Management Systems
Typical TWSC Rural Expressway Intersection INTRODUCTION • What is a Rural Expressway? • A high speed (> 50 mph), multi-lane, divided highway with partial access control. • Typically divided by a wide, depressed, turf median • Presents a combination of at-grade intersections & grade separated interchanges
Converting 2-Lane Highways to Expressways • Popular Highway Safety Improvement In Many States • Why? • Provide Freeway Capacity @ Lesser Expense • Make Passing Easier/Safer • Reduce Likelihood of Head-On & Opposite Direction Sideswipe Collisions • Expressways Fastest Growing Component in US Highway System • Expressway Mileage Increased 2600 miles (1996 – 2002) • Expansion Expected to Continue • 26/28 DOT’s Plan to Expand Expressway System Over Next 10 Years
Nebraska Expressway System ( 600 Miles Functionally Classified as Expressway)
PROBLEM STATEMENT • Right-Angle Intersection Collisions on Rural Expressways Are Reducing the Safety Benefits That Should Be Achieved When Converting Rural 2-Lane Highways To Expressways
PROBLEM STATEMENT • Problem Not Specific To Nebraska • Minnesota, Utah, & Iowa Data Have Shown Similar Trends • Greater Than 50% of Expressway Intersection Crashes are Right-Angle Collisions • 2004 Mn/DOT Study Discovered . . . • Rural expressway intersections have a greater proportion of right-angle collisions than intersections on 2-lane highways. • 87% of right-angle crashes were due to inability of minor road drivers to select safe gaps. • 78% of right-angle crashes were “far-side” collisions. • Intersection recognition by drivers on minor approaches was not a contributing factor.
Typical TWSC Rural Expressway Intersection PROBLEM STATEMENT SUMMARY • Primary Rural Expressway Intersection Safety Problem is Right-Angle, Far-Side Collisions • Underlying Cause = Poor Gap Selection Choices By Left-Turning & Crossing Minor Road Drivers
PROJECT OBJECTIVES • Active Project NCHRP 15-30 • Recommending improvements to the AASHTO Green Book & MUTCD regarding intersection design on rural expressways. http://www4.trb.org/trb/crp.nsf/NCHRP+projects (Click on Area 15) • TASKS • Review Current Green Book & MUTCD Design Guidance (Identify Areas Where Guidance is Lacking) • Literature Review (Identify Safe Design Treatments) • Survey of State DOTs (Case Studies of Innovative Intersection Design Treatments) • Develop Recommended Text for the Green Book & MUTCD
Potential Rural Expressway Intersection Safety Treatments • DOT’s Have Experimented with a Wide Range of Intersection Safety Treatments at Problematic Rural Expressway Intersections to Improve Safety Performance While Avoiding Costly Grade Separation. • These Treatments Can Be Divided Into 3 Broad Categories • Conflict Point (Access) Management • Gap Selection Aids • Intersection Recognition Devices
CONFLICT POINT MANAGEMENT • Conflict points represent the locations where vehicle paths cross as they move from one leg to another. • Conflict point management treatments remove, reduce, or control the number and type of conflicts that can occur at an intersection. • Intersection conflict point analysis suggests that the more conflict points an intersection design has, the more dangerous it will be. • Assumes crash risk is equal at each conflict point • However, the crash risk associated with each point actually varies depending on the complexity and volumes of the movements involved.
CONFLICT POINT MANAGEMENT • Conflict Point Management Treatments Include: • Conversion to Grade Separation/Interchange • Use of Frontage Roads to Remove Low Volume Intersections • Conversion of 4-Legged Intersections to 3-Legged • Use of Indirect Movements • J-Turn Intersection Design • Loops • Jug-Handles • Providing Left/Right-Turn Lanes or Longer Lanes • Providing Right-Turn Ramps • Reducing Median Opening Length • Signalization
CONVERSION TO T-INTERSECTIONS • Crash models developed in NCHRP 375 (1995) revealed that crash frequency and rates at 3-legged expressway intersections are substantially lower than at 4-legged. • This has long been acknowledged since 3-legged intersections have fewer conflict points • 4-Legged Expressway Intersection = 42 • 3-Legged Expressway Intersection = 11 (75% less) • Therefore, converting four-legged expressway intersections to three-legs should improve rural expressway intersection safety • Alabama DOT has experienced positive results
Offset T-Intersection • Right-Left Configuration Preferred over Left-Right • Proper Spacing? • 500 Feet to ½ Mile (Minimum Intersection Spacing Used) • Identifying Opportunities to Create Offset T Intersections should be part of initial expressway corridor development process.
One-Quadrant Interchange US-34 North of Emerson, IA
J-TURN INTERSECTION • “The ability to accommodate high volumes of traffic safely and efficiently through intersections depends largely on the arrangements provided for handling intersecting traffic.” – AASHTO Green Book, p. 743 • The greatest crash risk movements (i.e., those accounting for the greatest share of crashes) at rural expressway intersections are typically the minor road left-turn and crossing maneuvers.
J-TURN INTERSECTION • J-Turn Intersection is a directional median opening combined with 2 median U-turns that allows left-turning traffic off the expressway, but forces left-turning and crossing minor road traffic to turn right, merge left, make a U-turn, and return to the intersection. • “There is no indication that U-turns at unsignalized median openings constitute a safety concern.” – NCHRP 524 (2004) • 24 Total Conflict Points
J-TURN INTERSECTION • “J-Turn” Coined by Maryland DOT in 2000 when they constructed one at JCT US-301 & MD-313 • Maryland’s experience has shown that J-Turn Intersections can offer superior safety performance. • U-Turn Spacing (Maryland Design = 1500 feet) • Disadvantage – Wide Median Width Required to Accommodate U-Turns
J-TURN INTERSECTION • “For U-turn openings designed specifically for the purpose of eliminating the left-turn movement at a major intersection, they should be designed with a median left-turn lane.” – AASHTO GB, p. 710 • Minimum Median Widths to Accommodate U-Turns by Different Design Vehicles: * For all calculations, 12 foot wide lanes assumed
J-TURN INTERSECTION Special U-Turn Treatments With Narrow Medians
CONCLUSIONS • Far-side, right-angle collisions at TWSC rural expressway intersections are reducing the safety benefits that should be achieved when converting rural two-lane highways to expressways. • The treatments described in this presentation • Converting 4-legged Intersections to 3-legs • J-Turn Intersections seem to have the greatest potential to improve rural expressway intersection safety while avoiding costly grade separation. • Use of these strategies should be considered at intersections with safety concerns as well as during expressway corridor planning.
FUTURE WORK • Further research is necessary to. . . • Determine the actual crash reduction potential of these treatments • Determine volume warrants for these treatments or under what conditions these treatments are most appropriate.
ACKNOWLEDGMENTS • Dr. Tom Maze (ISU) – P.I. (NCHRP 15-30) • Dr. Souleyrette (ISU) • Tom Welch (Iowa DOT) • Howard Preston (CH2MHILL) • Richard Storm (CH2MHILL) • Dave Peterson (NDOR)
QUESTIONS? For Copy of Paper/Presentation or Any Additional Questions: Contact Info: Joshua L. Hochstein (515) 294-7188 email@example.com