Synthesis of Safety for Traffic Operations - Transports Canada

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Synthesis of Safety for Traffic Operations March 2003 Lalani (1991) The City of San Buenaventura, California as part of a Comprehensive Safety Program introduced 2WLTLs to five areas of the city (Lalani, 1991). Sites were selected because they were considered high crash locations. The analysis was a naïve before-after analysis using crash frequency and one-year before and after periods. Details of the treatment are not reported (i.e., what was the original cross-section? And was reconstruction required?). The results of the analysis are shown in Table 9.12. TABLE 9.12: Safety Impacts of 2WLTLs in San Buenaventura, California Location Crashes Before After CMF A 18 9 0.50 B 9 5 0.56 C 8 5 0.63 D 3 1 0.33 E 25 11 0.31 Totals 73 31 0.42 Lalani does not account for exposure in the safety analysis but reports that traffic volumes in the city increase at an average rate of 6% per annum. Furthermore, there is no information provided on access density. Bonneson and McCoy (1997) Bonneson and McCoy (1997) developed crash prediction models to assess the safety impacts of median treatment on urban and suburban arterial roads in Omaha, Nebraska and Phoenix, Arizona. Roads included in the dataset shared the following characteristics: • Annual traffic volume in excess of 7000; • Speed limit between 30 and 50 mph; • 350 foot or more signalized intersection spacing; • Direct access from abutting properties; and • No more than 3 lanes in each direction Three years of crash data were used in the analysis. Crashes excluded from the database included signalized intersection-related crashes, and crashes resulting from extraordinary circumstances (i.e., driving under the influence, and crashes on snow covered streets). Overall 126.5 kilometres of street and 6,391 crashes were included in the analysis. The equations were developed using generalized linear regression assuming a negative binomial distribution. They are as follows: Page 117
Turn Lanes A T = ADT 0.91 L 0.852 e (-14.15 + 0.018Ib – 0.093Ir + 0.0077(DD+SD)Ib + 0.0255PDO) [9.1] A U = ADT (0.91+1.021Ir) L 0.852 e (-14.15 – 10.504Ir + 0.57Ip + 0.0077(DD+SD)Ib + 0.0255PDO) [9.2] where: A T = Annual number of accidents for streets with 2WLTLs A U = Annual number of accidents for undivided streets ADT = Annual daily traffic L = Length of street (metres) DD = driveway density (/km) SD = unsignalized intersection density (/km) PDO = proportion of property damage only crashes (%) Ib = Business land use (=1 if business or office use, =0 otherwise) Ir = Residential land use (=1 if residential or industrial, =0 otherwise) Ip = Parking (=1 if parallel, curbside parking permitted, =0 otherwise) Therefore, to determine the safety impacts of a 2WLTL installation, the analyst should estimate the annual crash frequency produced by each equation, and compare the results. Tople (1998) Tople (1998) in an evaluation of hazard elimination and safety projects included a review of the safety benefits of 2WLTLs that were introduced through pavement markings, and through reconstruction. The documentation available does not indicate if the 2WLTLs created through pavement markings were a result of a four-lane cross-section being converted to three lanes, or if a wide two-lane street was restriped as a three lane street. In any event, the evaluation was a naïve before-after study of crash frequency and crash severity. The impact on crash severity was determined through a comparison of equivalent property damage only crashes, using monetary conversations deemed appropriate by the investigation team. Three years of before and three years of after crash data was used in the analysis. The results of the analysis are presented in Table 9.13. The Tople analysis possesses many potentially serious flaws. Most importantly, the sites were selected for treatment as part of a safety program. This means that the crash record was likely abnormally high, and there is a great potential for regression to the mean artefacts. This shortcoming is likely offset somewhat by a failure to account for changes in exposure. Traffic volumes were not controlled for, but typically volumes tend to increase which would lead to a higher “after” count of crashes. In the end, the South Dakota results are based on a limited number of sites and weak analyses. Page 118
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Transport Canada Transports Canada
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Synthesis Of Safety For Traffic Ope
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DISCLAIMER The material presented h
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EXECUTIVE SUMMARY Traffic operation
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Synthesis of Safety for Traffic Ope
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TABLE OF CONTENTS DISCLAIMER REJET
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LIST OF TABLES TABLE 3.1: Crash Rat
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Chapter 1: Chapter 1: Introductio I
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Introduction Before proceeding, a f
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Introduction Literature regarding t
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Introduction The current science of
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Introduction adequate size control
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Introduction In concluding this sec
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Chapter 3: Chapter 3: Intersectio I
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Intersection Control TABLE 3.3: Cra
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Intersection Control TABLE 3.5: CMF
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Intersection Control Vancouver Regi
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Intersection Control V m = the sum
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Intersection Control where: X1 = 0
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Intersection Control Region of Durh
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Intersection Control TABLE 3.17: CM
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Intersection Control The predictor
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Intersection Control program includ
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Intersection Control TABLE 3.26: Me
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Intersection Control TABLE 3.29: St
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Intersection Control TABLE 3.32: Ni
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Intersection Control It is noted th
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Intersection Control Sayed et al (1
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Intersection Control Signal Clearan
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Intersection Control The CMFs are 0
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Intersection Control also examined
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Intersection Control Shebeeb (1995)
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Intersection Control approaches at
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Intersection Control TABLE 3.56: Sa
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Chapter 5: Chapter 5: Pavement Pave
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Pavement Markings The study methodo
Page 107 and 108: Pavement Markings Hall (1987) Hall
Page 109 and 110: Pavement Markings TABLE 5.8: Safety
Page 111 and 112: Pavement Markings THIS PAGE IS INTE
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Page 124: Chapter 7: Chapter 7: Bicycle Bicyc
Page 127 and 128: Bicycle Safety TABLE 7.1: Safety Im
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Page 151 and 152: Turn Lanes TABLE 9.2: Safety Impact
Page 153 and 154: Turn Lanes Vogt determined that a l
Page 155 and 156: Turn Lanes 1998 one of their high c
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Page 161 and 162: Turn Lanes CMF = 1 - 0.7 P lt/d 0.0
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Page 168 and 169: TABLE 10.3: Speed Changes Resulting
Page 170 and 171: Sites Where Applied 1 URBAN Island
Page 172 and 173: Forbes and Gill (2000) undertook a
Page 174 and 175: Ideally, three years of before and
Page 176 and 177: Kermit and Hein (1962) looked into
Page 178 and 179: The effects of the transverse pavem
Page 180: Chapter 11: Chapter 11: Other Other
Page 183 and 184: Other Safety Issues collisions per
Page 185 and 186: Other Safety Issues THIS PAGE IS IN
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References References
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References Bloch SA (1998) “Compa
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References Hamilton Associates (199
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References Lee JT, Maleck TL, and T
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References Polanis SF (1998) “Do
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References Vancouver, City of (1999
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References THIS PAGE IS INTENTIONAL
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Appendix B: Critical R Appendix B:
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Critical Reviews Worksheet for Eval
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Critical Reviews 2. Are the expecte
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Appendix D: Appendix D: How to Use
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How to Use Safety Performance Funct
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How to Use Safety Performance Funct
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Synthesis of Safety for Traffic Operations - Transports Canada

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