All local agencies wrestle with safety concerns, regardless of how many miles of streets they maintain.  They may be related to vehicle crashes, bike safety, or pedestrian worries.  News flash – there are no magical answers and engineering alone cannot solve all of our problems.  Public education, law enforcement, and the threat of real penalties for risky driving (and risky biking and pedding for that matter) have to be layered onto the physical improvements we make to the roadway, the bike paths, and the pedestrian routes and crossings.

The good news is that, on the engineering front, there are a collection of proven countermeasures we can apply to minimize risks for all modes of traffic.  If you haven’t already browsed the 28 proven safety countermeasures from the Federal Highway Administration (FHWA), take a moment and browse them as a starter.

Another gem is the Crash Modification Factors (CMF) Clearinghouse.  It is literally a warehouse of techniques that have been studied and found to reduce crashes under certain circumstances.  Fair enough; it is not literally a physical warehouse, but it feels like it.  If you haven’t had a look, you just haven’t had your geek on recently.  Grab a cup of caffeinated something or other and take a little tour.

Now, for some of you, it might seem a bit intimidating; don’t let it be. With a little orientation, you will find it is mostly straightforward and if you need some coaching, that’s what we are here for (our technical assistance is a free service for Delaware local agencies, so put us to work).  But, bear a couple of things in mind if you are new to the Clearinghouse.

First, you can browse through CMFs if that’s your style, but you can also use the search function, which is robust.  Let’s say you are working on some pedestrian crossing concerns.  Enter “pedestrian” in the search and you will find various categories you can open and browse the countermeasures under each.  For example, you will find results for Rapid Rectangular Flashing Beacons (RRFBs), high-visibility crosswalks, raised crosswalks, and more.  Just have fun with it.

Next, what is a CMF?  When a countermeasure is researched by departments of transportation, local agencies, designers, and academics, they determine from before and after crash data the degree to which the techique has been effective under the circumstances studied.  The reduction in crashes is referred to a CMF.  For example, if a study shows that crashes before the countermeasure were, say, 100 in a five year period and they were 70 after the countermeasure was deployed, the CMF would be 0.7 (think 70%).  An inverse terms is sometimes used, the Crash Reduction Factor (CRF); you can use either, but CMF is the coolest and most hip term.  In our example, the CRF would be 30% (i.e., crashes were reduced by 30%).

Now, don’t be lulled in by an exciting countermeasure that promises a CMF of 0.35.  That sounds great (okay, zero would be better, but we don’t have any of those), but you want to look at the conditions where they found that.  For example, it may have been on a rural road and your concern is urban, so you’ll want to look at others, although you can still read through the research to see if you can glean any morsels from it.  You may also find that the particular CMF applies only to fatal crashes and your issue has been more about serious injuries or possible injuries (or even close calls).  You may find that the CMF applies only to bike crashes but you are also concerned about pedestrians, so keep browsing.  Try to find the one that matches your circumstances the closest.

Third (fourth?  We lost count), don’t be overly charmed with the quality star rating itself.  It can be a measure of the strength of the research, but before jumping at a countermeasure, follow the “read more” link in most CMF comments and scroll down to the “view the fully study details” link for a little more insight.

If you would like to dig deeper, the research citation is usually there.  In fairness, these can be a little hard to locate as they are specialty works.  But we will help look if you’re feeling curious.  For example, many citations are from Elvik, R. and Vaa, T., “Handbook of Road Safety Measures.” Oxford, United Kingdom, Elsevier, (2004).  This is now a collectors item and if you have one, hold onto it (but share).  The second edition is pretty pricey, but we have access to it online through the University of Delaware Morris Library, so we can dig into it if you like.

As a final guide, it is helpful to know the KABCO injury classification.  Under “crash severity,” you will see K, A, B, C, and O indicators.  Crashes involving a fatal injury are K.  Crashes involving serious injury are A.  Crashes involving a non-serious injury are B.  Crashes involving a possible injury are C.  Crashes involving no injuries are O.

Oh, we’ve made it seem complicated.  It’s really not.  Want to see an introduction to the Clearinghouse, what they research, and how to apply CMFs?  Watch their December 2022 webinar.

What do you do with the information?  How is it useful to you?  Well, some of you have limited funds and have to prioritize your actions.  Even if you have unlimited safety funds (good for you), adopting countermeasures all willy nilly can be ineffective at best and can even be counterproductive (yes, there are countermeasures with a negative CMF, meaning you can make it worse under some circumstances).

So, how do you decide?  There are some complicated analysis tools that are appropriate for high crash areas where there is sufficient data to employ the techniques in the Highway Safety Manual (and they involve differential equations, which are icky), but for most local roads, the CMF Clearinghouse, together with the FHWA Proven Safety Countermeasures, is sufficient to select a countermeasure or a collectdion of them appropriate for your concern.

These tools help you narrow down to one or two countermeasures to deploy.  Experience shows that making just one or two changes at a time is best, because if you deploy multiple measures all at once, you can’t be sure which were most effective and, at best, you may have wasted money and effort.  You can layer on other techniques at a later date if you feel they will be value-added.

The Delaware T2/LTAP Center’s Municipal Engineering Circuit Rider is intended to provide technical assistance and training to local agencies and so if you have roadway safety concerns or other transportation issues, contact Matt Carter at or (302) 831-7236.

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