Developing Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects (2021) / Chapter Skim
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34 Chapter 5. Crash Reduction Effectiveness of Specific Design Improvement Types 3R programs are managed by highway agencies as part of their effort to preserve pavements and extend their service life.
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35 reduce crashes. A CMF value greater than 1.0 indicates that the design feature or treatment would be expected to increase crashes.
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36 centerline rumble strips can range from a CMF of 0.76 to a CMF of 0.96, or a reduction of crashes in the range from 4 to 24 percent. Such uncertainties are typical of even the most reliable CMFs, given the variations inherent in crash data.
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37 would have been expected if the project had not been implemented is estimated with a crash prediction model known as a safety performance function (SPF)
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38 Further guidance on CMF development is found, in HSM Chapter 9 (6) and in the FHWA report, A Guide to Developing Crash Modification Factors (33)
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39 Table 24. CMF for Lane Width on Rural Two-Lane Roadway Segments (6, 10, 34, 35)
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40 πΆππΉ πΆππΉ 1.0 π 1.0 (3) where: CMFra = crash modification factor for the effect of lane width on target or "related" crashes (i.e., single-vehicle run-off-the-road and multiple-vehicle head-on, opposite-direction sideswipe, and same-direction sideswipe crashes)
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41 NOTE: Based on HSM Figure 10-8. Figure 3.
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42 Table 26. CMFs for Shoulder Types and Shoulder Width on Roadway Segments (CMFtra)
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43 5.2.1.5 Centerline Rumble Strips HSM Chapter 10 includes a CMF for the effects of a centerline rumble strip on a rural two-lane highway (6)
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44 Table 27. Roadside Slope CMFs for Rural Two-Lane Highways (40)
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45 These CMFs apply to left- or right-turn lanes installed on signalized intersection approaches or uncontrolled major-road approaches to stop-controlled intersections, but do not apply to stopcontrolled approaches to stop-controlled intersections. 5.2.2 Rural Multilane Undivided Highways 5.2.2.1 Lane Width The CMF for lane widths on multilane undivided roadways is determined using the equations in Table 30 (6)
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46 NOTE: Based on HSM Figure 11-8. Figure 4.
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47 represent the best available estimate of the effect of superelevation variance on crash frequency for curves on rural multilane undivided highways. 5.2.2.4 Centerline Rumble Strips No CMFs are available for the effect of centerline rumble strips on rural multilane highways.
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48 Table 31. Roadside Slope CMFs for Rural Multilane Highways (6)
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49 5.2.3 Rural Multilane Divided Highways (Nonfreeways) 5.2.3.1 Lane Width The CMF for lane width on multilane divided roadways is determined using the equations in Table 34 (6)
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50 The CMFs shown in Table 34 and Figure 5 are applicable to single-vehicle run-off-the-road, multiple-vehicle head-on, opposite-direction sideswipe, and same-direction sideswipe crashes. Equation (3)
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51 5.2.3.6 Striping and Delineation The MoDOT evaluation (39) also presents results for rural multilane divided highways.
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52 Table 37. CMFs for Installation of Right-Turn Lanes on Intersection Approaches (6)
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53 5.2.4.5 Centerline Rumble Strips NCHRP Report 641, Guidance for the Design and Application of Shoulder and Centerline Rumble Strips (38) , found that centerline rumble strips on urban two-lane arterials reduce total target crashes by 40 percent, corresponding to a CMF of 0.60.
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54 Table 39. CMFs for Installation of Right-Turn Lanes on Intersection Approaches (6)
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55 shows the coefficient values that are used in Equation (11)
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57 If a continuous median barrier is adjacent to one of the directions of travel, but not centered in the median, use Equation (18)
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58 Use Equations (23)
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59 Table 44. Coefficients for Median Width on Freeways (7)
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