Decision-Making Guide for Traffic Signal Phasing (2020) / Chapter Skim
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From page 70... ...
62 11 Combining Safety and Operations 11.1 Relationship When selecting the most appropriate phase mode and sequence, the user must consider both safety and operations, as shown in Figure 19. In some cases, promoting safety may lead to a degradation in operational performance and vice versa.
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63 11.2.1 Step 1. Estimate Annual Delay Cost The first step of the process is to estimate the annual delay costs, in dollars, of each phasing alternative under consideration.
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64 Table 6 - CMFs Derived from Research Treatment Crash Type CMFs Estimate Standard error Convert from permissive-only or protected-permissive left-turn phasing to protected-only left-turn phase on major road LTOPP1 0.507 0.070 LTOPP INJ2 0.443 0.073 Convert from permissive-only or protected-permissive left-turn phasing to protected-only left-turn phase on minor road LTOPP1 0.702 0.098 LTOPP INJ2 0.687 0.109 Convert from protected-only left-turn phasing to permissive-only or protected-permissive left-turn phasing on major road LTOPP1 1.973 0.273 LTOPP INJ2 2.259 0.374 Convert from protected-only left-turn phasing to permissive-only or protected-permissive left-turn phasing on minor road LTOPP1 1.424 0.198 LTOPP INJ2 1.457 0.231 1. Left-turn Opposing Crash, All Severities 2.
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65 where, Costi = Composite Estimated Annual Cost of phasing alternative i, in dollars ($) Delayi = Estimated Annual Delay Cost of phasing alternative i, in dollars ($)
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66 Volumes The major road approach has an AADT of 14,000 vehicles per day, and the minor road approach has an AADT of 3,600 vehicles per day, as obtained from the state AADT database. Turning movement counts for 24-hours are available for use in this analysis because data were collected for the earlier signal warrant study.
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67 Estimate Annual Delay Cost This analysis employed a deterministic model to determine the delay per vehicle for a typical AM, PM, Midday, and off-peak hour, shown in Table 8. The deterministic model relied on software-optimized signal timings based on the lane configuration and volume inputs.
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From page 76... ...
68 Table 10 - Case Study 1a - Annual Delay Cost Scenario 1 Scenario 2 Annual Delay 15,203 hours 25,017 hours Annual Delay Cost, Delayi $ 227,741 $ 374,755 11.3.2 Estimate Annual Crash Cost Since representative crash data are not available, the safety analysis relied on the SPFs developed by the accompanying research effort. Chapter 9 provides more detail on the use of SPFs.
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69 πΆππ π‘ = π·ππππ¦ + πΆπππ β where, Costi = Composite Cost of phasing alternative I, in dollars ($) Delayi = Estimated Annual Delay Cost of phasing alternative, in dollars ($)
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From page 78... ...
70 Table 15 - Case Study 1b - Annual Delay Cost Scenario 1 Scenario 2 Annual Delay 44,496 hours 70,103 hours Annual Delay Cost, Delayi $ 666,550 $ 1,050,143 Table 16 - Case Study 1b - Annual Crash Cost Scenario 1 Scenario 2 Annual Crashes (KABC Severities) 0.287 0.146 Annual Crash Cost, Crashi $ 32,291 $ 16,427 Table 17 - Case Study 1b - Annual Composite Cost Scenario 1 Scenario 2 Annual Delay Cost, Delayi $ 666,550 $ 1,050,143 Annual Crash Cost, Crashi $ 32,291 $ 16,427 Annual Composite Cost, Costi $ 698,841 $ 1,066,570 At this intersection, Scenario 1 (protected-permissive left-turn phasing)
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71 Table 18 - Case Study 2 - Annual Delay Cost Scenario 1 Scenario 2 Annual Delay 15,203 hours 25,017 hours Annual Delay Cost, Delayi $ 227,741 $ 374,755 Estimate Annual Crash Cost The annual crash frequency and crash cost for Scenario 2 remain the same as in Case Study 1a. However, the estimated annual crash frequency for Scenario 1 (the existing condition)
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From page 80... ...
72 where, Costi = Composite Cost of phasing alternative I, in dollars ($) Delayi = Estimated Annual Delay Cost of phasing alternative, in dollars ($)
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