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The National Academies

NCHRP 22-39 [Active]

Guardrail Performance at Various Offsets from Curb MASH TL-3 Applications

  Project Data
Funds: $600,000
Staff Responsibility: David M. Jared
Research Agency: University of NE - Lincoln
Principal Investigator: Mr. Scott Rosenbaugh
Effective Date: 6/3/2019
Completion Date: 6/2/2022

BACKGROUND
 
Curbs are used to control drainage, separate pedestrian facilities, limit right-of-way, provide access control, and limit erosion. However, the need for curbs often competes with guardrail installation. For example, a steep slope needs curb to control drainage and erosion. This steep slope may need shielding. If a pedestrian facility is near curb, the guardrail will have to be further offset from the face of curb. Typical solutions for curb placed near a guardrail, like using a sloped curb or reducing curb height, can be difficult to use and may cause problems for sight-impaired pedestrians who may unexpectedly enter the roadway.  Shorter curbs may not have the hydraulic capacity needed. In addition, fill condition behind the curb, curb transition, and termination adjacent to guardrail may cause vehicle instability at impact. Using curbs to solve one problem may create an entirely new problem.
 
Most research on curb and guardrail used the NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features testing criteria. The American Association of State Highway and Transportation Officials (AASHTO) and Federal Highway Administration’s (FHWA) joint Manual for Assessing Safety Hardware (MASH) agreement requires the use of MASH evaluated hardware.
 
Some crash tests have involved curb placed near guardrail. Many of these tests have failed due to guardrail rupture, barrier override, or vehicle instability. Traditionally crash testing has focused on the performance of pickup trucks striking guardrail with a nearby curb. Some recent crash testing has indicated that additional research is needed on small cars hitting a guardrail near a curb due to the difference of vertical loading upon impact versus that of a pickup truck.  Crash testing guardrail installed near a curb with pickup trucks has shown the limitations in using just computer modeling to set guardrail placement recommendations. More recent crash testing results, that involve the use of a different guardrail, and change in crash test criteria call into question how well guardrail performs near a curb. Further research is needed and should be conducting using the most commonly used generic guardrail system, the 31-in. Midwest Guardrail System (MGS).
 
OBJECTIVE
 
The objective of this research is to develop guidelines for the use and placement of the 31-in. MGS adjacent to curbs under MASH TL-3 impact conditions. The guidelines are to consider the effect of curb geometry, fill condition behind the curb, curb termini, block-out depth, barrier offset from the curb, and barrier height relative to the roadway on the performance of the guardrail.  It is anticipated that a combination of previous research, computer simulation modeling, and full-scale crash testing will be required to develop and verify the guidance to demonstrate MASH compliance.
 
RESEARCH PLAN
 
The NCHRP is seeking the insights of proposers on how best to achieve the research objective. Proposers should develop and include in their proposal a detailed research plan for accomplishing the project objective. Proposers are expected to describe research plans that can realistically be accomplished within the constraints of available funds and contract time. Proposals must present the proposers' current thinking in sufficient detail to demonstrate their understanding of the issues and the soundness of their approach to meet the research objective. 
 
The research plan should be divided into tasks, and proposers must describe in detail the work proposed in each task. The research plan should also include a description of proposed deliverables for each task or group of tasks along with a detailed project schedule. Deliverables should include an interim report prepared approximately half-way through the project that describes work completed in early tasks. This interim report should also include an updated work plan for remaining tasks and an annotated outline of the final report deliverable(s) that will require NCHRP approval prior to proceeding with subsequent tasks. The interim report will be presented at a face-to-face meeting with the NCHRP project panel. The research plan should also include an appropriate number of web-enabled teleconferences (including one within 1 month of the contract’s execution date). NCHRP will host the web-conferences and provide the meeting venue for the face-to-face meeting with the NCHRP project panel.
 
Final deliverables should include: 
  • A final report to include:
    1. Documentation of the research effort;
    2. Stand-alone guidelines, including any drawings and/or specifications in a format suitable for consideration by AASHTO for use in a future update to the Roadside Design Guide (RDG).
    3. Documentation of recommended MGS placement configurations, simulation model results, and crash test results including videos in a format that can be used by a state department of transportation to illustrate MASH compliance.
    4. Recommendations for additional needed future research.
  • A PowerPoint presentation with speaker notes that summarizes the project describing the background, objectives, research method, findings, and conclusions.
Note: Following receipt of the draft final deliverables, the remaining 3 months shall be for NCHRP review and comment and for research agency preparation of the final deliverables.
 
STATUS: Research in progress.

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