FHWA Guide to Developing CMFs

Applications, new CMFs and Crash Modification Factors Clearinghouse

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FHWA Guide to Developing CMFs

Postby khardy » Wed Dec 01, 2010 9:45 am

FHWA has published "A Guide to Developing Quality Crash Modification Factors."

http://safety.fhwa.dot.gov/tools/crf/re ... wasa10032/
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Re: FHWA Guide to Developing CMFs

Postby jlaplante » Fri Dec 17, 2010 7:11 pm

I have a major concern that the results of NCHRP 3-72 were not included in the Urban Arterial portion of the Highway Safety Manual. As I hope you are all aware, this study found that there was no significant crash difference between 10, 11 and 12-foot lanes on urban arterial roadways with posted speed limits less than 45 mph. In my mind, this would seem to indicate a CMF of 1.00 for lane widths between 10 and 12 feet. Was this an oversight or was there some reason for this serious lack of information, since this is a major source of discussion and conflict among state and local roadway engineers. I intend to bring this matter up at the HSM Subcommittee meeting at TRB, but any advance information or discussion would be much appreciated.
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Re: FHWA Guide to Developing CMFs

Postby jshaw » Thu Dec 23, 2010 7:43 am

John, I'm not certain I understand your concern. For Urban/Suburban Arterials, lane width is not a component of the predictive method -- it is not a variable in the base equations and there would be no reason to have a CMF of 1.00 for different geometric values if there is no expected change. Is it that the subject of lane width in the urban/suburban context received no discussion in Chapter 12 that has you concerned?
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Re: FHWA Guide to Developing CMFs

Postby Jonathan.Nelson » Thu Dec 23, 2010 8:33 am

I could be mistaken, but I think the omission of a CMF for lane width in the urban/suburban arterial chapter of the HSM is simply an acknowledgement that variance in lane width has no significant effect on crashes in the urban environment (as pointed out in NCHRP 3-72). Perhaps the chapter could have pointed this out, but I don't think it's necessarily an oversight. Since studies show there is no significant effect, then technically there is no need for a CMF.
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Re: FHWA Guide to Developing CMFs

Postby jlaplante » Tue Dec 28, 2010 12:54 pm

My concern about the omisssion of the CMF of 1.0 for the urban arterial lane widths is based on my personal experience trying to teach pedestrian and bicycle safety classes around the country and finding that the vast majority of practicing highway and traffic engineers have never heard of NCHRP 3-72 and firmly believe that bigger is better and that 12-foot lanes are thus preferred if there is adequate room. However, when it comes to reducing pedestrian crosswalk lengths or finding room for bike lanes, the wider lanes always seem to win out. If we can get the "no significant crash difference between 10, 11 and 12-foot lanes on urban arterials when the posted speed limit is 45 mph or less" message into an official AASHTO document, it will go a long way toward reeducating these engineers into allowing more pedestrian and bicycle-friendly roads in our cities and towns. If including 1.0 CMFs is not the appropriate method, there at least needs to be a statement giving this message included in the HSM.
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