Highway Safety Manual User Guide (2022) / Chapter Skim
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Pages 126-129
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From page 126... ...
126 4 HSM Part D: CMF Applications Guidance 4.1 Overview The HSM Part D provides information on the effectiveness of various safety treatments that can be used to estimate how effective how effective will be in reducing crashes at a specific location. This effectiveness is expressed in terms of CMFs values, trends, or no effect.
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From page 127... ...
SECTION 4 – PART D: CMF APPLICATIONS GUIDANCE 127 TABLE 73 Example Problem 9 – CMF Applications – Centerline Markings Expected Average Crash Frequency FatalandInjury PDO Total All Crash Types 24 76 100 Run-off-the-Road Crashes 15 49 64 CMF – Centerline Markings CMF SE Centerline Markings – Fatal-and-Injury 0.99 0.06 Centerline Markings - PDO 1.01 0.05 Injury PDO Expected Crashes with Treatment 23.76 76.76 Change in Expected Crashes -0.24 0.76 Confidence Intervals Low High Fatal-and-Injury 0.87 1.11 PDO 0.91 1.11 95th Percentile Confidence Interval Estimation of Crashes Confidence Interval Range Variation Low High Δ Low Δ High Δ % Low Δ % High Fatal-and-Injury 20.88 26.64 -3.12 2.64 -13% 11% PDO 69.16 84.36 -6.84 8.36 -9% 11% The CMFs and the relevant standard errors for centerline rumble strips on rural two-lane highway are listed in HSM Table 13-46 (HSM p.
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From page 128... ...
SECTION 4 – PART D: CMF APPLICATIONS GUIDANCE 128 TABLE 74 Example Problem 9 – CMF Applications – Centerline Rumble Strips Part 2 Run-off-the-Road – Injury 0.35 1.15 95th percentile Confidence Interval Estimation of Crashes Confidence Interval Range Variation Low High Δ Low Δ High Δ % Low Δ % High All Severities 76.0 96.0 -24 -4 -24% -4% Injury 16.6 24.2 -7.44 0.24 -31% 1% Run-off-the-Road – All Severities 37.8 63.4 -26.2 -0.6 -41% -1% Run-off-the-Road – Injury 5.3 17.3 -9.8 2.3 -65% 15% 4.2.4 Results and Discussion Based on the CMFs in HSM Table 13-38, the fatal-and-injury crashes will decrease 0.24 crash per year and PDO crashes will increase 0.76 crash per year after placing the centerline markings. With the application of the centerline rumble strips and based on HSM Table 13-46, the total crashes and fatal-and-injury crashes will decrease 14 and 3.6 per year, respectively; and for roadway departure crashes, the total crashes and fatal-and-injury crashes will decrease 13.4 and 3.8, respectively.
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From page 129... ...
SECTION 4 – PART D: CMF APPLICATIONS GUIDANCE 129 4.3 Example Problem 10: Improving Urban Four-Leg Signalized Intersection 4.3.1 Introduction An urban four-leg signalized intersection was identified as candidate for roadway modifications after applying the roadway safety management process on the selected roadway network. The safety engineer requested a list of possible treatments for the intersection that have specific CMF and standard error values.
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