Evaluation of Safety Strategies at Signalized Intersections (2011)

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7Provided in this chapter is a summary of the literature review and the identification of future and ongoing research. Given that the focus of this effort was on developing CMFs, the initial screening criterion applied to each study was that the results must be founded on a crash-based analysis (as opposed to analyses of driver behaviors, citations, or other “surrogate” measures). Hence, the focus of this review was on studies that evaluated treatments at signalized intersections using crash-based analysis. The studies for each treatment were further screened to determine which ones included the development of CMFs or a methodology that may be used to develop CMFs. The studies meeting this criterion and believed to be the most credible were then subjected to a more critical review. Each critical review was undertaken with the follow- ing objectives: 1. Evaluate the research approach and statistical methodology, including an investigation of the potential for pitfalls such as regression-to-the-mean (RTM) or site-selection bias. A thorough discussion of these possible pitfalls is presented in NCHRP Synthesis 295: Statistical Methods in Highway Safety Analysis (Persaud, 2001). 2. Document the magnitude and assess the confidence level of any CMFs produced. The results of the critical reviews are organized by strategies listed from NCHRP Report 500, Volume 12. One of the out- comes from the critical reviews was the confidence level of the CMFs of each treatment. This qualitative measure reflects the level of predictive certainty in the CMF derived and is a reflection of the study methodology. The confidence lev- els and the levels of predictive certainty can be qualified as follows: • High—The CMF was developed in a rigorous observational before-after study that incorporates what are currently con- sidered the best study design and statistical analysis methods, namely the empirical Bayes (EB) method described by Hauer (1997) or the full Bayes (FB) method. • Med-High—The CMF was developed in a before-after study that incorporated sound (but not the current state-of-the-art) statistical methods and/or may not have been reviewed and “vetted” by an expert panel of researchers (as were the CMFs in the Highway Safety Manual). This level would also include CMFs that result from the combination of findings from different (i.e., less controlled) before-after and cross- sectional studies by an expert research panel. The panel’s judgment concerning the certainty level of the CMF would be reflected in our rating. This level would also include CMFs that have been developed in a rigorous meta-analysis by a recognized meta-analysis expert. (Meta-analysis is the combination of the results of various studies using tech- niques that allow the expert to accommodate some of the shortcomings of the original research.) • Low-Med—The CMF was developed from cross-sectional analysis (controlling for other factors statistically), or less- than-rigorous before-after studies still judged to be of value (e.g., a before-after study in which regression-to-the-mean was not viewed as a major potential bias due to the fact that “high-crash locations” were not selected for the treatment of the evaluation). • Low—The CMF was developed in a simple before-after study without control for regression to the mean and other confounders, or from cross-sectional studies where model- ing techniques and assumptions are questionable. Table 2.1 shows the predictive certainty for each treatment, along with the key reference. C H A P T E R 2 Literature Review

Strategy Name P, T, or E1 Predictive Certainty Key References 17.2 A1: Employ multiphase signal operation – protected left-turn signal phase P Medium-High • Harkey et al., 2008. 17.2 A1: Employ multiphase signal operation – permissive- protected or protected-permissive left-turn signal phase P? Medium-High • Lyon et al., 2005. 17.2 A1: Employ multiphase signal operation – split phases T Non-Existent No key studies hgiH-muideMPslavretniecnaraelcezimitpO:2A2.71 • Retting et al., 2002 muideM-woLPlavretniecnaraelcderllA:2A2.71 • Souleyrette et al., 2004 • Polanis, 2002 17.2 A3: Restrict or eliminate turning maneuvers using channelization or signing T Non-Existent No key studies 17.2 A3: Introduce/Prohibit RTOR T Medium-High • Harkey et al., 2008 serusaemetagorrusesuseidutsgniwollofehTtnetsixE-noNPnoitanidrooclangisyolpmE:4A2.71 (which are not yet proven) to try to deduce the effect on safety. • Rakha et al., 2000 • Berg et al., 1986 seidutsyekoNtnetsixE-noNPnoitpmeerpelcihevycnegremeyolpmE:5A2.71 17.2 A6: Improve operation of pedestrian and bicycle facilities at signalized intersections: • Pedestrian signs, signals, and markings • Crossing guards for school children • Lights in crosswalks in school zones • Pedestrian-only phase or pedestrian-lead phase during signal operation Combination of P and T Low for Pedestrian Signals • Zegeer et al., 1982 • Elvik and Vaa, 2004 17.2 A6: Improve operation of pedestrian and bicycle facilities at signalized intersections: Prohibition of RTOR Combination of P and T Low-Medium • Preusser et al., 1982. hgiHPslangisdetnarrawnuevomeR:7A2.71 • Persaud et al., 1997. 1 P (proven), T (Tried), and E (Experimental); From NCHRP Report 500, Volume 12. Table 2.1. Key references for strategies/treatments from NCHRP Report 500, Volume 12, along with level of predictive certainty.

Strategy Name P, T, or E1 Predictive Certainty Key References 17.2 B1: Provide or improve left-turn channelization: Providing left-turn lanes Combination of P and T High • Harwood et al., 2002. 17.2 B1: Provide or improve left-turn channelization: Lengthening left-turn lanes Combination of P and T Low • Harwood et al., 2002. 17.2 B1: Provide or improve left-turn channelization: Providing left-turn lanes: Providing positive offset for left-turn lanes Combination of P and T High • Khattak et al., 2004. • Persaud et al., 2009. 17.2 B1: Provide or improve left-turn channelization: Providing positive guidance with channelization Combination of P and T Non-Existent No Key Studies 17.2 B1: Provide or improve left-turn channelization: Delineating turn path Combination of P and T Non-Existent No Key Studies 17.2 B2: Provide or improve right-turn channelization: add exclusive right-turn lane P High • Harwood et al., 2002. 17.2 B2: Provide or improve right-turn channelization: provide channelization that includes raised or painted islands P Non-Existent The following two studies may evaluate the safety aspects of different types of channelization treatments: • NCHRP Project 3-78 (ongoing) • NCHRP Project 3-89 (ongoing) Psenalnrut-thgirnehtgneL:2B2.71 Non-Existent No Key Studies 17.2 B3: Improve geometry of pedestrian and bicycle facilities: • Continuous sidewalks • Signed and marked crosswalks • Sidewalk set-backs • Median refuge areas • Pedestrian overpasses • Intersection lighting • Physical barriers to restrict pedestrian crossing maneuvers • Relocation of transit stops • Other traffic calming applications Combination of P and T Non-Existent The following studies the safety effects of marked versus unmarked crosswalks at unsignalized locations. It is not clear if the results are transferable to signalized locations: • Zegeer et al., 2001 17.2 B4: Revise geometry of complex intersections – convert a four-leg intersection to two T intersections T Non-Existent The following study did a meta-analysis based on 9 studies that had looked at the effects of 1 P (proven), T (Tried), and E (Experimental); From NCHRP Report 500, Volume 12. (continued on next page)

Strategy Name P, T, or E1 Predictive Certainty Key References converting four-leg to two T intersections. However, the study does not report whether these intersections are signalized or not. • Elvik and Vaa, 2004. 17.2 B4: Revise geometry of complex intersections – convert two T intersections to one four-leg intersection T Non-Existent No key studies 17.2 B4: Revise geometry of complex intersections – improve intersection skew angle P Non-Existent No key studies 17.2 B4: Revise geometry of complex intersections – Remove deflection in through-vehicle travel path T Non-Existent No key studies 17.2 B4: Revise geometry of complex intersections – Close intersection leg T Non-Existent No key studies 17.2 B5: Construct special solutions: provide indirect left turn T Non-Existent No key studies 17.2 B5: Construct special solutions: Convert to roundabout T Medium High • Persaud et al., 2001. • Rodegerdts et al., 2007. 17.2 B5: Construct special solutions: Convert two-way streets to a one-way pair T Non-Existent The following studies report reduction in pedestrian crashes, but no information is available about the methodology that was used: • Wiley, 1959 • Karagheuzoff, 1972 17.2 B5: Construct special solutions: Construct interchange or grade separation T Non-Existent The following study did a meta-analysis based on 4 studies. However, none of these studies were from the USA: • Elvik and Vaa, 2004 seidutsyekoNtnetsixEn-oNTselgnairtthgisraelC:1C2.71 seidutsyekoNtnetsixEn-oNPsehcaorppanoitcesretningisedeR2:C2.71 17.2 D1: Improve visibility of intersections on approach(es) • Improve signing and delineation • Install larger signs T Non-Existent No key studies 17.2 D1: Improve visibility of intersections on approach(es): Provide intersection lighting T Low-Medium • Lipinski and Wortman, 1976 • Preston and Schoenecker, 1999. • Walker and Roberts, 1976. • Donnell et al., 2009. • Harkey et al., 2008. 1 P (proven), T (Tried), and E (Experimental); From NCHRP Report 500, Volume 12. Table 2.1. (Continued).

Strategy Name P, T, or E1 Predictive Certainty Key References 17.2 D1: Improve visibility of intersections on approach(es) • Install rumble strips on approaches • Install queue detection systems • Install red-light hold systems T Non-Existent No key studies 17.2 D1: Improve visibility of intersections on approach(es): Install dynamic advance-warnings flashers ‘Red Signal Ahead’ T Low • Sayed et al., 1999. 17.2 D2: Improve visibility of signals and signs at intersections: Install additional signal heads T Medium High • Harkey et al., 2008. 17.2 D2: Improve visibility of signals and signs at intersections: • Provide visors to shade signal heads • Provide louvers, visors, or special lenses so drivers are able to view signals only for their approach • Install backplates T Medium High for Signal Lens Upgrade The following study conducted a before-after EB evaluation using a combination of different treatments to improve visibility. Different groups of intersections had a slightly different set of treatments. However, results were not disaggregated by type of treatment: • Sayed et al., 2007. 17.2 D2: Improve visibility of signals and signs at intersections: Install larger (12 inch) signal lenses T High • Sayed et al., 1998. • Harkey et al., 2008. 17.2 D2: Improve visibility of signals and signs at intersections: • Remove or relocate unnecessary signs • Provide far-side left-turn signal T Non-Existent No key studies seidutsyekoNtnetsixEn-oNTnoitacudednanoitamrofnicilbupedivorP1:E2.71 17.2 E2: Provide targeted conventional enforcement of traffic laws T Non-Existent No key studies 17.2 E3: Implement automated enforcement of red-light running P High • Council et al., 2005. • Shin and Washington, 2006 • Miller et al., 2006. 17.2 E4: Implement automated enforcement of approach speeds T Non-Existent The following studies looked at the effect of automated enforcement on safety at different corridors, but did not report on crashes at signalized intersections: • Cunningham et al., 2005. • Chen et al., 2002. • Mountain et al., 2004. 1 P (proven), T (Tried), and E (Experimental); From NCHRP Report 500, Volume 12. (continued on next page)

Strategy Name P, T, or E1 Predictive Certainty Key References 17.2 E5: Control speed on approaches: • Construct a horizontal curve to reduce speeds • Speeding vehicle activated traffic signals • Traffic calming treatments E Non-Existent No key studies 17.2 F1: Restrict access to properties using driveway closures or turn restrictions T Low • Xu, 2001 17.2 F2: Restrict cross-median access near intersections T Non-Existent No key studies 17.2 G1: Improve drainage in intersection and on approaches T Non-Existent No key studies 17.2 G2: Provide skid resistance in intersection and on approaches T High • Harkey et al., 2008. 17.2 G3: Coordinate closely spaced signals near at-grade railroad T Non-Existent No key studies crossings 17.2 G4: Relocate signal hardware out of clear zone T Non-Existent No key studies 17.2 G5: Restrict or eliminate parking on intersection approaches P Non-Existent The following study did a meta-analysis based on 13 studies that had looked at the effects of changes in parking. However, it is not clear how many of the locations were close to signalized intersections: • Elvik and Vaa, 2004. 1 P (proven), T (Tried), and E (Experimental); From NCHRP Report 500, Volume 12. Table 2.1. (Continued).