Joshua L' Hochstein

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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
• [phone]
• jlhoax_at_iastate.edu

2006 Mid-Continent Transportation Research
Forum Madison, WI 8/17/2006
Iowa State Universitys 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
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NCHRP 15-30PROJECT OBJECTIVES

• Recommend improvements to the AASHTO Green Book
  MUTCD regarding intersection design on rural
  expressways.

• PROJECT TASKS
• Review Design Guidance Currently Provided
• Literature Review
• Case Studies on Effectiveness of 10 Rural
  Expressway Intersection Safety Treatments
• Develop Recommended Text for Green Book MUTCD

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PRESENTATION OVERVIEW

• Define rural expressway.
• Explain the rural expressway intersection safety
  problem.
• Describe practical design alternatives for TWSC
  rural expressway intersections.

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RURAL EXPRESSWAY A high speed (gt 50 mph),
multi-lane, divided highway with partial access
control consisting of both at-grade intersections
and grade separated interchanges.
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2-Lane Undivided Expressway

• Popular Highway Safety Improvement
• Expressway Mileage Increased ? 2600 miles
  (1996 2002)
• Many STAs Plan to Expand Expressway Systems Over
  Next 10 Years

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2-Lane Undivided Expressway

• Why?
• Makes Passing Easier/Safer
• Reduces Likelihood of Head-On Opposite
  Direction Sideswipe Collisions
• Provide Interstate Capacity Mobility at Lesser
  Cost

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Nebraskas Rural Expressway System
I-80
Rural Expressways (? 600 Miles Functionally
Classified as Expressway)
Purpose Connect Urban Centers with each other
and to I-80
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PROBLEM STATEMENT

• Right-Angle Intersection Collisions on Rural
  Expressways Are Reducing the Safety Benefits That
  Should Be Achieved When Converting Undivided
  Rural 2-Lane Highways To Expressways

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PROBLEM STATEMENT

• Problem Not Specific To Nebraska
• Minnesota, Utah, Iowa Data Have Shown
• gt 50 of Expressway Intersection Crashes
• are Right-Angle Collisions

• 2004 Mn/DOT Study Discovered . . .

• Intersection recognition by drivers on minor
  approaches was not a contributing factor.

• 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.

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PROBLEM STATEMENT

• Typical Problem Right-Angle, Far-Side Collisions

• Underlying Cause Poor Gap Selection Choices By
  Left-Turning Crossing Minor Road Drivers

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Potential Rural Expressway Intersection Safety
Treatments

• STAs Have Experimented with a Wide Range of
  Intersection Safety Treatments While Trying to
  Avoid Signalization or Grade Separation.

• These Treatments Can Be Divided Into 3 Broad
  Categories
• Conflict Point (Access) Management
• Gap Selection Aids
• Intersection Recognition Devices

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CONFLICT POINT MANAGEMENT

• Conflict points represent the locations where
  vehicle paths cross as they move from one leg to
  another.

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CONFLICT POINT MANAGEMENT

• 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 treatments remove,
  reduce, or control the number and type of
  conflicts that can occur at an intersection.

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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

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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.

• 3-legged intersections have fewer conflict points
• 4-Legged Expressway Intersection 42
• 3-Legged Expressway Intersection 11 (75 less)

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Offset T-Intersection
26 conflict points

• 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.

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One-Quadrant Interchange
US-34
North of Emerson, IA
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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.

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J-TURN INTERSECTION
24 Total Conflict Points

• J-Turn Intersection is a directional median
  opening combined with 2 median U-turns.
• Allows left-turning traffic off the expressway
• 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)

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J-TURN INTERSECTION

• J-Turn Coined by Maryland DOT in 2000 when they
  constructed one at JCT US-301 MD-313

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J-TURN INTERSECTION

• Marylands experience has shown that J-Turn
  Intersections can offer superior safety
  performance and public acceptance.

• U-Turn Spacing (Maryland Design 1500 feet)

• Disadvantage Wide Median Width Required to
  Accommodate U-Turns

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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
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J-TURN INTERSECTION

• Special U-Turn Treatments With Narrow Medians

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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
• Converting 4-legged Intersections to 3-legs
• J-Turn Intersections
• seem to have potential for improving rural
  expressway intersection safety while avoiding
  signalization grade separation.

• Use of these strategies should be considered at
  intersections with safety concerns as well as
  during expressway corridor planning.

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FUTURE WORK

• Further research is necessary to. . .
• Determine the actual crash reduction potential of
  these treatments (in progress).
• Determine volume warrants for these treatments or
  under what conditions these treatments will be
  most effective and are most appropriate.

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ACKNOWLEDGMENTS

• Dr. Tom Maze (Iowa State University)
• Howard Preston (CH2MHill)
• Richard Storm (CH2MHill)
• Tom Welch (Iowa DOT)
• Dave Peterson (Nebraska DOR)
• Robert Kiel (Maryland SHA)

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QUESTIONS?
Paper on Conference CD For Copy of Presentation
or Any Additional Questions Contact
Info Joshua L. Hochstein (515)
294-5642 jlhoax_at_iastate.edu