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The National Academies

NCHRP 15-64 [Active]

Guidelines for the Design of Unsignalized Median Openings in Close Proximity to Signalized Intersections

  Project Data
Funds: $325,000
Staff Responsibility: Waseem Dekelbab
Research Agency: Texas A&M Transportation Institute
Principal Investigator: Karen Dixon, Ph.D.
Effective Date: 8/22/2016
Completion Date: 8/22/2018

BACKGROUND
 
The operational and safety performance resulting from unsignalized median openings in close proximity to signalized intersections is not clear and merits further investigation. Many agencies discourage access within the functional area of a signalized intersection as recommended in current access management guidance. Guidance suggests that unsignalized median openings be bidirectional openings designed for left-turns from the roadway (and possibly U-turns) only. Closely spaced median openings result in a complex pattern of overlapping conflicts and a resulting range of safety and operational impacts. Full access intersections may be unnecessary and result in negative impacts on traffic operations. Managing access in most cases is the best solution; however, there is little guidance on what parameters should be considered when selecting between full versus restricted access medians. In addition, removing movements reduces conflict points and when located and designed correctly, an unsignalized median opening may improve operations of a signalized intersection. There is a need to provide guidelines on the design of median openings to improve safety and operations of these access points.
 
OBJECTIVE
 
The objective of this research is to develop guidelines for transportation agencies to evaluate the safety and operational effects of the location and design of unsignalized median openings in close proximity to signalized intersections. The guidelines should address the following subject areas:
 
 Safety
  • Crash data
  • Conflict points
  • Highway Safety Manual (HSM) predictive analysis
Operations
  • Speed
  • Traffic
  • Modes
  • Freight
Design/Implementation
  • Geometry
  • Sustainability
  • Public involvement
  • Context – rural/urban
  • Effective practices
  • New vs. retrofit
 
 The final deliverables shall include:
  • A standalone guidelines document
  • A final report documenting the conduct of the research
  • A technical memorandum titled “Implementation of Research Findings and Products” (see Special Note C)
  • Recommendations for revisions to existing reference documents (HSM, Green book, Access Management Manual) arising from this research
  • A PowerPoint presentation and training materials suitable for NHI or a webinar
 
STATUS: Research in progress

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