CMF on Increasing Intersection Median Width (Table 14-17)

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CMF on Increasing Intersection Median Width (Table 14-17)

Postby cherylb » Tue Oct 02, 2012 10:30 am

In looking at the CMF for Increasing Intersection Median Width in Part D, Table 14-17, the question came up about the treatment of increasing intersection median width by 3-ft increments. This can imply that you can multiply the CMF for every 3 feet, so if you start with a 14 ft median and add six feet at a rural, four-leg unsignalized intersection (CMF=0.96) can use a CMF of 0.96*0.96, so a CMF of 0.92 could be used? Could this be done all the way up to 80 feet? (this doesn't seem quite right, as it would give a CMF of 0.41)

I would appreciate any suggestions on how this CMF is intended to be applied. Thanks!
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Re: CMF on Increasing Intersection Median Width (Table 14-17

Postby mdimaiuta » Wed Oct 03, 2012 1:07 pm

Cheryl,

I interpret Table 14-17 the same as you. That is, starting with a base condition of a 14-ft-wide to 80-ft-wide median -- a CMF of 0.96 would be applied for every 3-ft increase in median width (for multiple-vehicle crashes at rural 4-leg signalized intersections). So, as you noted, for a base condition of 14-ft, a proposed 20-ft wide median would have a CMF of 0.96 * 0.96 = 0.92. I assume that this could be done all the way up to 80-ft, resulting in a CMF = 0.41 for increasing the width from 14-ft to 80-ft.

Mike Dimaiuta
IHSDM / HSM Support
ihsdm.support@dot.gov
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Re: CMF on Increasing Intersection Median Width (Table 14-17

Postby cherylb » Tue Dec 18, 2012 11:06 am

I must've forgotten to ask for an alert when there was a reply, but thanks for the info, Mike! Very helpful.
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