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CMB in Wide Medians

Question
State CA
Description Text

I'm writing to ask if the Midwest States Pooled Fund Crash
Test Program has done any research on the use of cable barriers in wide medians
(greater than 75 feet). I'm conducting some research on behalf of California
Department of Transportation into practices and guidance for the use of
barriers in wide medians. Is that a subject that the pooled fund has
investigated? I'd appreciate any information you can offer.

Keywords
  • Guardrail
Other Keywords Cable Median Barrier
Date May 13, 2015


Response
Response

There is some available data that suggests there is a benefit to placing CMBs in medians wider than 70-75 ft, but there is a distinguishable reduction in the benefit-to-cost ratio. I have attached a report, Reducing Median Crossover Crashes in Wisconsin, which is abbreviated “CMC in Wisconsin.pdf”. In it there is a chart showing the total cross-median crash data collected in Wisconsin by median width on Page 11. Several crashes occurred in medians of 75 ft wide or greater.

Similar analysis of crashes in medians in North Carolina shown on Page 7 of the attached PDF titled Median Barriers in North Carolina and denoted as “NCDOT -  Summer TRB Presentation on Cable experience.pdf” indicated that even at moderate to low traffic volumes for divided rural interstates, cross-median crashes (CMCs) still occurred when median widths were in excess of 75 ft:

Dr. Dean Sicking, Karla Lechtenberg, and Dr. F. Daniel B. Albuquerque conducted a study evaluating cross-median crashes and cable median barrier warrants based on interstate data in Kansas. That report is titled Cable Median Barrier Guidelines and denoted as “TRP-03-206-08-Final-Revised.pdf”, and is available from the Pooled Fund website under TRP-03-206-08. Although the frequency of crashes occurring in medians wider than 70 ft was limited, there was at least a limited risk that crashes could occur in wider medians.

Likewise, TTI issued some guidance for the state of Texas in 2006 titled Median Barrier Guidelines for Texas and denoted as “TTI Report No. 0-4254-1.pdf”. On page 33, TTI noted that the majority of TX’s cross-median crash data occurred in medians larger than 60 ft wide. The disproportionate representation of wide median CMC data is partially because TX is proactive in shielding medians narrower than 70 ft, but it is reflective of the need to consider shielding even in wide medians. This was reinforced in a 2009 report titled Development of Guidelines for Cable Median Barrier Systems in Texas. denoted as “Development of Guidelines for CMB in Texas - TTI 2009.pdf”.

Other data may also be available, but the brief synopsis suggests that for large traffic volumes, CMBs may be warranted for medians wider than 75 ft. Unfortunately there are currently no recommendations available to establish guidelines for usage, and states may determine if there are locations in which barriers placed in these wide medians are justified.

Date May 13, 2015
Attachment CMC in Wisconsin.pdf
Attachment NCDOT - Summer TRB Presentation on Cable experience.pdf
Attachment Development of Guidelines for CMB in Texas - TTI 2009.pdf


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