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29 CHAPTER 6 Compilation of CMFs This Chapter includes Tables 6.1 through 6.5 which show the and a description of the sites used in the study (along with the CMFs that were developed for each treatment that was evalu- range of AADT values) are provided along with the CMFs and ated in this study. For each treatment, the study methodology the standard error of the CMFs.

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Table 6.1. Evaluation of installing dynamic signal warning flashers. TREATMENT: Install Dynamic Signal Warning Flashers METHODOLOGY: Cross-Sectional Regression Model CRASH TYPE STUDIED AND ESTIMATED EFFECTS Sites CMF (S.E. of REFERENCE: NCHRP 17-35 Final Report Crash Type and Severity with CMF) DSWF STUDY SITES: All Crashes 0.814 (0.062)# Data from Virginia and Nevada were used to develop the recommended Rear-End Crashes 0.792 (0.079)# CMFs for Dynamic Signal Warning Flashers (DSWF). 30 Angle Crashes 0.745 (0.086)# 15 intersections with DSWF in Virginia and 15 intersections with DSWF Injury and Fatal Crashes 0.820 (0.083)# in Nevada were used in the cross-sectional models (along with Heavy Vehicle Crashes 0.956 (0.177) intersections without DSWF). # Statistically significant at the 0.05 level (based on ideal standard errors) For intersections with DSWF in Virginia, the average major road AADT was 18,729 (minimum major road AADT was 7,500 and maximum major road AADT was 33,000) and the average minor road AADT was 2,408 (minimum minor road AADT was 40 and the maximum minor road AADT was 5,000). For intersections with DSWF in Nevada, the average major road AADT was 36,329 (minimum major road AADT was 9,765 and maximum major road AADT was 99,000) and the average minor road AADT was 7,263 (minimum minor road AADT was 1,300 and the maximum minor road AADT was 20,100). COMMENTS: The analysis included different methods: cross-sectional models, before-after with comparison group, and before-after EB methods. The results from the cross-sectional models were found to be the most reliable.

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Table 6.2. Evaluation of converting a signalized intersection to a roundabout. Treatment: Convert Signalized Intersection to Roundabout METHODOLOGY: Before-After EB CRASH TYPE STUDIED AND ESTIMATED EFFECTS REFERENCE: NCHRP Project 17-35 No. of Condition, Crash Type, and Severity Improved CMF (S.E. of CMF) STUDY SITES: Sites Among the 28 sites, 3 were from Colorado, 1 from Florida, 3 All Crashes 0.792 (0.050)# from Indiana, 2 from Maryland, 2 from Michigan, 2 from North Carolina, 11 from New York, 1 from South Carolina, 1 from All Crashes (CMFunction) 28 0.00004*AADT+0.303 Vermont, and 2 from Washington. Injury and Fatal Crashes 0.342 (0.058)# 2 lane roundabouts (all crashes) 0.809 (0.061)# 16 roundabouts were 2 lane and the remaining 12 roundabouts were single lane. 15 roundabouts were from suburban areas and 2 lane roundabouts (Injury and Fatal 16 the remaining 13 were from urban areas. 6 of the roundabouts Crashes) 0.288 (0.065)# were 3 leg and the remaining 22 were 4 leg. 1 lane roundabouts (all crashes) 0.735 (0.086)# 1 lane roundabouts (Injury and Fatal 12 In the before period, the average total intersection AADT was 18,529 (minimum AADT was 5,322 and maximum AADT was Crashes) 0.451 (0.115)# 43,123). Suburban (all crashes) 0.576 (0.053)# 15 Suburban (Injury and Fatal Crashes) 0.259 (0.066)# Urban (all crashes) 1.150 (0.093) 13 Urban (Injury and Fatal Crashes) 0.445 (0.100)# 3 leg roundabouts (all crashes) 1.066 (0.163) 3 leg roundabouts (Injury and Fatal 6 Crashes) 0.370 (0.172)# 4 leg roundabouts (all crashes) 0.759 (0.052)# 4 leg roundabouts (Injury and Fatal 22 Crashes) 0.338 (0.061)# COMMENTS: # Statistically significant at the 0.05 level. For total crashes, the average CMF was 0.792. However, this CMF was found to be a function of AADT and so a CMFunction was estimated. The CMFunction is valid between total intersection AADT of about 5,300 to about 43,000. For injury crashes, the CMF was not found to be a function of AADT. * represents a product, i.e., 0.00004*AADT is the product of 0.00004 and AADT.

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Table 6.3. Evaluation of increasing signal change interval. TREATMENT: Increase Signal Change Interval METHODOLOGY: Before-After EB CRASH TYPE STUDIED AND ESTIMATED EFFECTS REFERENCE: NCHRP Project 17-35 final report No. of Treatment, Crash Type, and Severity Treated CMF (S.E. of CMF) STUDY SITES: Sites Increase Yellow and All Red (All) 0.991 (0.146) The sample included 2 sites from Howard County, Maryland, 6 sites from Montgomery County, Maryland, 16 Increase Yellow and All Red (Injury & Fatal) 1.020 (0.156) 11 sites from San Diego, California, and 7 sites from San Increase Yellow and All Red (Rear end) 1.117 (0.288) Francisco, California. Increase Yellow and All Red (Angle) 0.961 (0.217) In the before period, the average major road AADT was Increase Yellow Only (All) 1.141 (0.177) 17,417 (minimum major road AADT was 5,950 and Increase Yellow Only (Injury & Fatal) 1.073 (0.216) maximum major road AADT was 31,600) and the average 5 minor road AADT was 8,484 (minimum minor road AADT Increase Yellow Only (Rear end) 0.934 (0.237) was 2,650 and the maximum minor road AADT was Increase Yellow Only (Angle) 1.076 (0.297) 20,225). Increase All Red Only (All) 0.798 (0.074)# Modifications to the yellow and all red time were not Increase All Red Only (Injury & Fatal) 0.863 (0.114) 14 equivalent for all sites. For sites where both the yellow and Increase All Red Only (Rear end) 0.804 (0.135) all red time were increased, the average increases in the Increase All Red Only (Angle) 0.966 (0.164) yellow and all red times were 0.8 seconds and 1.0 seconds, respectively. For sites where only the yellow interval was Increase Change Interval (< ITE) (All) 0.728 (0.077)# increased, the average increase in the yellow interval was 1.0 Increase Change Interval (< ITE) (Injury & seconds. For sites where only the all red interval was Fatal) 0.662 (0.099)# 12 increased, the average increase in the all red time was 1.1 Increase Change Interval (< ITE) (Rear end) 0.848 (0.142) seconds. For sites where the total change interval was increased, but still less than the ITE recommended practice, Increase Change Interval (< ITE) (Angle) 0.840 (0.195) the average increase was 0.9 seconds. For sites where the total change interval was increased and exceeded the ITE Increase Change Interval (> ITE) (All) 0.922 (0.089) recommended practice, the average increase was 1.6 Increase Change Interval (> ITE) (Injury & seconds. Fatal) 15 0.937 (0.114) Increase Change Interval (> ITE) (Rear end) 0.643 (0.130)# The sample of sites used in this evaluation is limited. So these results should be used with due caution. Increase Change Interval (> ITE) (Angle) 1.068 (0.156) # Statistically significant at the 0.05 level.

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Table 6.4. Evaluation of changing left-turn phase from permissive to protected-permissive. TREATMENT: Change Left-Turn Phase (from Permissive to Protected-Permissive) METHODOLOGY: Before-After EB CRASH TYPE STUDIED AND ESTIMATED EFFECTS REFERENCE: NCHRP 17-35 Final Report Number of Treated Approaches and No. of CMF (S.E. of CMF) Crash Type at Intersection Level Sites STUDY SITES: Change from Permissive or Permissive/Protected 59 intersections from Toronto and 12 from North Carolina. All of them were four leg intersections from urban areas. All sites (all crashes) 71 1.031 (0.022) 1 treated approach (all crashes) 50 1.081 (0.027)# In Toronto, in the before period, the average major road AADT was 35,267 (minimum was 14,489 and maximum was 74,990) and the >1 treated approach (all crashes) 21 0.958 (0.036) average minor road AADT was 18,096 (minimum was 1,466 and All sites (injury and fatal crashes) 71 0.962 (0.035) maximum was 42,723). 1 treated approach (injury and fatal 50 0.995 (0.043) crashes) In North Carolina, in the before period, the average major road AADT was 12,302 (minimum was 4,857 and maximum was 18,766) >1 treated approach (injury and fatal 21 0.914 (0.055) and the average minor road AADT was 5,124 (minimum was 1,715 crashes) and maximum was 9,300). All sites (left-turn opposing through 71 0.862 (0.050)# crashes) COMMENTS: 1 treated approach (left-turn opposing 50 0.925 (0.067) through crashes) It is important to note that left-turn phasing was not constant >1 treated approach (left-turn opposing throughout the day for most of the sites (especially in Toronto), and 21 0.787 (0.072)# hence, the sites were categorized based on the predominant phasing through crashes) system. All sites (rear-end crashes) 71 Among the 21 sites where more than 1 approach was treated, 17 of 1.075 (0.036)# them had 2 approaches treated, 2 of them had 3 approaches treated, 1 treated approach (rear-end crashes) 50 1.094 (0.045)# and 2 of them had 4 approaches treated. >1 treated approach (rear-end crashes) 21 1.050 (0.059) # Statistically significant at the 0.05 level.

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Table 6.5. Evaluation of implementing protected-permissive phasing with flashing yellow arrow for the permissive phase. TREATMENT: Implement Protected-Permissive Phasing with Flashing Yellow Arrow for the Permissive Phase METHODOLOGY: Combination of EB before-after and CRASH TYPE STUDIED AND ESTIMATED EFFECTS Comparison Group REFERENCE: NCHRP 17-35 Final Report No. of CMF (S.E. of Before Period and Crash Type Sites CMF) STUDY SITES: Five locations from Kennewich, WA, and 34 locations from Permissive or combination of permissive and protected-permissive (at Oregon were included in this evaluation. In Oregon, City of least 1 converted leg was permissive in the before period) Beaverton provide data for 15 sites, City of Gresham provided data Total intersection crashes 0.753 (0.094)# for 6 sites, City of Oregon City provided data for 3 sites, and City of 9 Portland provided data for 10 sites with FYA. Data were obtained Intersection left-turn crashes 0.635 (0.291)# from 16 sites in urban areas from North Carolina. Protected-Permissive (all converted legs had protected-permissive in the before period) For the sites from Kennewich, WA, the average major road AADT in the before period was 18,568 (minimum was 11,443 and Total intersection crashes 0.922 (0.104) maximum was 22,756) and the average minor road AADT was 6,729 13 Intersection left-turn crashes 0.806 (0.146) (minimum was 3,020 and maximum was 11,765). Protected (all converted legs had protected in the before period) For the sites from Oregon, the average major road AADT in the before period was 22,490 (minimum was 8,260 and maximum was Total intersection crashes 1.338 (0.097)# 29 32,350) and the average minor road AADT in the before period was Intersection left-turn crashes 2.242 (0.276)# 3,455 (minimum was 780 and maximum was 10,620). # Statistically significant at the 0.05 level. For the sites from North Carolina, the average major road AADT in the before period was 24,206 (minimum was 9,100 and maximum was 43,000), and the average minor road AADT in the before period was 5,048 (minimum was 660 and maximum was 11,350). COMMENTS: The sample for the conversion from permissive or permissive/protected to FYA is limited. So these results should be used with due caution.