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29 This Chapter includes Tables 6.1 through 6.5 which show the CMFs that were developed for each treatment that was evalu- ated in this study. For each treatment, the study methodology and a description of the sites used in the study (along with the range of AADT values) are provided along with the CMFs and the standard error of the CMFs. C H A P T E R 6 Compilation of CMFs
TREATMENT: Install Dynamic Signal Warning Flashers METHODOLOGY: Cross-Sectional Regression Model CRASH TYPE STUDIED AND ESTIMATED EFFECTS REFERENCE: NCHRP 17-35 Final Report Crash Type and Severity Sites with DSWF CMF (S.E. of CMF) STUDY SITES: ⢠Data from Virginia and Nevada were used to develop the recommended CMFs for Dynamic Signal Warning Flashers (DSWF). ⢠15 intersections with DSWF in Virginia and 15 intersections with DSWF in Nevada were used in the cross-sectional models (along with intersections without DSWF). ⢠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). All Crashes 30 0.814 (0.062)# Rear-End Crashes 0.792 (0.079)# Angle Crashes 0.745 (0.086)# Injury and Fatal Crashes 0.820 (0.083)# Heavy Vehicle Crashes 0.956 (0.177) # Statistically significant at the 0.05 level (based on ideal standard errors) 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. Table 6.1. Evaluation of installing dynamic signal warning flashers.
Treatment: Convert Signalized Intersection to Roundabout METHODOLOGY: Before-After EB CRASH TYPE STUDIED AND ESTIMATED EFFECTS REFERENCE: NCHRP Project 17-35 Condition, Crash Type, and Severity No. of Improved Sites CMF (S.E. of CMF) STUDY SITES: ⢠Among the 28 sites, 3 were from Colorado, 1 from Florida, 3 from Indiana, 2 from Maryland, 2 from Michigan, 2 from North Carolina, 11 from New York, 1 from South Carolina, 1 from Vermont, and 2 from Washington. ⢠16 roundabouts were 2 lane and the remaining 12 roundabouts were single lane. 15 roundabouts were from suburban areas and the remaining 13 were from urban areas. 6 of the roundabouts were 3 leg and the remaining 22 were 4 leg. ⢠In the before period, the average total intersection AADT was 18,529 (minimum AADT was 5,322 and maximum AADT was 43,123). All Crashes 28 0.792 (0.050)# 303.0+TDAA*40000.0)noitcnuFMC(sehsarCllA )850.0(243.0sehsarClataFdnayrujnI # 2 lane roundabouts (all crashes) 16 0.809 (0.061)# 2 lane roundabouts (Injury and Fatal Crashes) 0.288 (0.065)# 1 lane roundabouts (all crashes) 12 0.735 (0.086)# 1 lane roundabouts (Injury and Fatal Crashes) 0.451 (0.115)# Suburban (all crashes) 15 0.576 (0.053) # Suburban (Injury and Fatal Crashes) 0.259 (0.066)# Urban (all crashes) 13 1.150 (0.093) Urban (Injury and Fatal Crashes) 0.445 (0.100)# 3 leg roundabouts (all crashes) 6 1.066 (0.163) 3 leg roundabouts (Injury and Fatal )271.0(073.0)sehsarC # 4 leg roundabouts (all crashes) 22 0.759 (0.052)# 4 leg roundabouts (Injury and Fatal )160.0(833.0)sehsarC # 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. Table 6.2. Evaluation of converting a signalized intersection to a roundabout.
TREATMENT: Increase Signal Change Interval METHODOLOGY: Before-After EB CRASH TYPE STUDIED AND ESTIMATED EFFECTS REFERENCE: NCHRP Project 17-35 final report Treatment, Crash Type, and Severity No. of Treated Sites CMF (S.E. of CMF) STUDY SITES: ⢠The sample included 2 sites from Howard County, Maryland, 6 sites from Montgomery County, Maryland, 16 sites from San Diego, California, and 7 sites from San Francisco, California. ⢠In the before period, the average major road AADT was 17,417 (minimum major road AADT was 5,950 and maximum major road AADT was 31,600) and the average minor road AADT was 8,484 (minimum minor road AADT was 2,650 and the maximum minor road AADT was 20,225). ⢠Modifications to the yellow and all red time were not equivalent for all sites. For sites where both the yellow and all red time were increased, the average increases in the yellow and all red times were 0.8 seconds and 1.0 seconds, respectively. For sites where only the yellow interval was increased, the average increase in the yellow interval was 1.0 seconds. For sites where only the all red interval was increased, the average increase in the all red time was 1.1 seconds. For sites where the total change interval was increased, but still less than the ITE recommended practice, the average increase was 0.9 seconds. For sites where the total change interval was increased and exceeded the ITE recommended practice, the average increase was 1.6 seconds. ⢠The sample of sites used in this evaluation is limited. So these results should be used with due caution. Increase Yellow and All Red (All) 11 0.991 (0.146) Increase Yellow and All Red (Injury & Fatal) 1.020 (0.156) Increase Yellow and All Red (Rear end) 1.117 (0.288) Increase Yellow and All Red (Angle) 0.961 (0.217) Increase Yellow Only (All) 5 1.141 (0.177) Increase Yellow Only (Injury & Fatal) 1.073 (0.216) Increase Yellow Only (Rear end) 0.934 (0.237) Increase Yellow Only (Angle) 1.076 (0.297) Increase All Red Only (All) 14 0.798 (0.074)# Increase All Red Only (Injury & Fatal) 0.863 (0.114) Increase All Red Only (Rear end) 0.804 (0.135) Increase All Red Only (Angle) 0.966 (0.164) Increase Change Interval (< ITE) (All) 12 0.728 (0.077)# Increase Change Interval (< ITE) (Injury & )990.0(266.0)lataF # Increase Change Interval (< ITE) (Rear end) 0.848 (0.142) )591.0(048.0)elgnA()ETI<(lavretnIegnahCesaercnI Increase Change Interval (> ITE) (All) 15 0.922 (0.089) Increase Change Interval (> ITE) (Injury & )411.0(739.0)lataF Increase Change Interval (> ITE) (Rear end) 0.643 (0.130)# )651.0(860.1)elgnA()ETI>(lavretnIegnahCesaercnI # Statistically significant at the 0.05 level. Table 6.3. Evaluation of increasing signal change interval.
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 Crash Type at Intersection Level No. of Sites CMF (S.E. of CMF) STUDY SITES: ⢠59 intersections from Toronto and 12 from North Carolina. All of them were four leg intersections from urban areas. ⢠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 average minor road AADT was 18,096 (minimum was 1,466 and maximum was 42,723). ⢠In North Carolina, in the before period, the average major road AADT was 12,302 (minimum was 4,857 and maximum was 18,766) and the average minor road AADT was 5,124 (minimum was 1,715 and maximum was 9,300). Change from Permissive or Permissive/Protected )220.0(130.117)sehsarclla(setisllA 1 treated approach (all crashes) 50 1.081 (0.027)# >1 treated approach (all crashes) 21 0.958 (0.036) All sites (injury and fatal crashes) 71 0.962 (0.035) 1 treated approach (injury and fatal crashes) 50 0.995 (0.043) >1 treated approach (injury and fatal crashes) 21 0.914 (0.055) All sites (left-turn opposing through crashes) 71 0.862 (0.050) # COMMENTS: ⢠It is important to note that left-turn phasing was not constant throughout the day for most of the sites (especially in Toronto), and hence, the sites were categorized based on the predominant phasing system. ⢠Among the 21 sites where more than 1 approach was treated, 17 of them had 2 approaches treated, 2 of them had 3 approaches treated, and 2 of them had 4 approaches treated. 1 treated approach (left-turn opposing through crashes) 50 0.925 (0.067) >1 treated approach (left-turn opposing through crashes) 21 0.787 (0.072) # All sites (rear-end crashes) 71 1.075 (0.036)# 1 treated approach (rear-end crashes) 50 1.094 (0.045)# >1 treated approach (rear-end crashes) 21 1.050 (0.059) ⢠# Statistically significant at the 0.05 level. Table 6.4. Evaluation of changing left-turn phase from permissive to protected-permissive.
TREATMENT: Implement Protected-Permissive Phasing with Flashing Yellow Arrow for the Permissive Phase METHODOLOGY: Combination of EB before-after and Comparison Group CRASH TYPE STUDIED AND ESTIMATED EFFECTS REFERENCE: NCHRP 17-35 Final Report Before Period and Crash Type No. of Sites CMF (S.E. of CMF) STUDY SITES: ⢠Five locations from Kennewich, WA, and 34 locations from Oregon were included in this evaluation. In Oregon, City of Beaverton provide data for 15 sites, City of Gresham provided data for 6 sites, City of Oregon City provided data for 3 sites, and City of Portland provided data for 10 sites with FYA. Data were obtained from 16 sites in urban areas from North Carolina. ⢠For the sites from Kennewich, WA, the average major road AADT in the before period was 18,568 (minimum was 11,443 and maximum was 22,756) and the average minor road AADT was 6,729 (minimum was 3,020 and maximum was 11,765). ⢠For the sites from Oregon, the average major road AADT in the before period was 22,490 (minimum was 8,260 and maximum was 32,350) and the average minor road AADT in the before period was 3,455 (minimum was 780 and maximum was 10,620). ⢠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). Permissive or combination of permissive and protected-permissive (at least 1 converted leg was permissive in the before period) Total intersection crashes 9 0.753 (0.094)# )192.0(536.0sehsarcnrut-tfelnoitcesretnI # Protected-Permissive (all converted legs had protected-permissive in the before period) Total intersection crashes 13 0.922 (0.104) )641.0(608.0sehsarcnrut-tfelnoitcesretnI Protected (all converted legs had protected in the before period) Total intersection crashes 29 1.338 (0.097)# )672.0(242.2sehsarcnrut-tfelnoitcesretnI # # Statistically significant at the 0.05 level. COMMENTS: ⢠The sample for the conversion from permissive or permissive/protected to FYA is limited. So these results should be used with due caution. Table 6.5. Evaluation of implementing protected-permissive phasing with flashing yellow arrow for the permissive phase.
