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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
RESEARCH PLAN

The NCHRP is seeking the insights of proposers on how best to achieve the research objective. Proposals are expected to describe a research plan that can realistically be accomplished within the constraints of available funds and contract time. Proposals must present the proposers' current thinking described in sufficient detail to demonstrate their understanding of the issues and the soundness of their approach to meeting the research objective. The work proposed must be divided into tasks and proposers must describe the work proposed in each task in detail. The tasks must be divided into two phases. Phase I will consist of information gathering and planning tasks, culminating in the submittal of an interim report. The interim report will describe the work completed in the Phase I tasks, include an annotated outline of the final guidelines, and provide an updated work plan for the Phase II tasks. The updated Phase II work plan should address the manner in which the proposer intends to use the information obtained in Phase I to satisfy the project objective. A face-to-face interim meeting with NCHRP will be scheduled to discuss the interim report. Work on Phase II tasks shall not begin until the updated work plan is approved by NCHRP. The project schedule should include 2 months for NCHRP review and approval of the interim report, and holding of the interim meeting.

The research plan shall include, but not be limited to:
  • A kick-off teleconference between the research team and NCHRP to be scheduled within 1 month of the contract’s execution to discuss the amplified work plan
  • A literature review to include domestic and international best practices
  • Detailed plans (including budget) for:
    • The collection of data to study the safety effects of unsignalized median  openings in close proximity to signalized intersections
    •  The collection of data to study the operational effects of unsignalized    median openings in close proximity to signalized intersections
 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
Proposers may recommend additional deliverables to support the project objective.

STATUS: Research in progress.

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