Synthesis of Safety for Traffic Operations - Transports Canada

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Synthesis of Safety for Traffic Operations March 2003 2WLTL Hoffman (1974) Hoffman (1974) examined the safety effects of constructing 2WLTLs on four four-lane arterial streets in Michigan. All of the streets had strip commercial development. The 2WLTL were provided with signs and pavement markings as prescribed by the standards of the day. Traffic volumes on the four streets ranged from 15,000 to 30,000 ADT. A total of 6.58 miles of 2WLTL were evaluated. The study methodology was a naïve before-after study using crash frequency as the measure of effectiveness. The results are shown in Table 9.9. Only one year of before and one year of after crash data were used in the analysis. TABLE 9.9: The Safety Impacts of 2WLTL in Michigan Crash Type No. Crashes Before After CMF Head-on 94 52 0.55 Rear-end 238 90 0.38 Right-angle 92 105 1.14 Sideswipe 42 39 0.93 Other 66 70 1.06 Total 532 356 0.67 The analysis does not account for exposure. Hoffman does mitigate this weakness by stating that the traffic volumes in the after period were about seven percent higher than the before period, suggesting that the safety benefit may be even greater. However, it is not clear why these sections of road were selected for treatment, and there may be a significant regression-to-the-mean bias. Furthermore, without a control group it is difficult to apportion to crash reduction to the 2WLTL installation. Main (1984) Main (1984) examined the effects of 2WLTLs on arterial streets in the City of Hamilton, Ontario. The 2WLTLs were five metres wide, marked and signed in accordance with the then current version of the Transportation Association of Canada’s Manual of Uniform Traffic Control Devices. All 2WLTLs were constructed on four lane roads, resulting in a five-lane cross-section. At the time only four sections of 2WLTL were available for analysis. The study methodology was a naïve before-after study using crash rate as the metric. Three years of before data were compared to one and two year after periods. The results are shown in Table 9.10. Page 115
Turn Lanes Section TABLE 9.10: Safety Impacts of 2WLTL Length Before After (km) # AWDT Rate # AWDT Rate CMF 1 0.5 49 22,390 4.17 12 + 23,050 2.98 0.71 2 0.5 63 22,560 5.32 11 + 22,030 2.86 0.54 3 0.4 114 24,190 11.23 32* 22,470 5.09 0.45 4 0.6 100 19,900 7.98 23* 19,400 2.83 0.35 Avg. 0.51 *Two years of data + one year of data Yagar and Van Aerde (1984) Yagar and Van Aerde (1984) studied the safety impacts of 2WLTLs on jurisdictions across Canada and the United States. Data was collected from road authorities via a survey, hence the configuration of the 2WLTLs and the settings in which they were implemented are expected to vary greatly within the dataset. Nonetheless, crash data was supplied for 30 road sections that had been provided with a 2WLTL. The study methodology was a naïve before-after study using crash frequency. The results are shown in Table 9.11. TABLE 9.11: Safety Impacts of 2WLTL in North America Crash Type No. of Sites No. of Crashes Before After CMF Left-turn from 2WLTL 14 130 83 0.64 Left-turn into 2WLTL 13 59 46 0.78 Left-turn from 2WLTL with leftturn 18 174 112 0.64 into 2WLTL No left-turn involved 21 817 513 0.62 All crashes 30 2479 1788 0.72 The analysis presented in the Yagar and Van Aerde study fails to account for exposure. However, elsewhere in the paper the authors examine the pre and post traffic volumes on the 2WLTL equipped streets, and the general trend appears to be an increase in traffic. This would mean the results of this study are conservative. The researchers did not gather any information on site selection processes, so the potential and magnitude of any regression-to-the-mean effects are unknown. Page 116
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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
Page 105 and 106: 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
Page 148: Chapter 9: Chapter 9: Turn Lanes Tu
Page 151 and 152: Turn Lanes TABLE 9.2: Safety Impact
Page 153 and 154: Turn Lanes Vogt determined that a l
Page 155: Turn Lanes 1998 one of their high c
Page 159 and 160: Turn Lanes A T = ADT 0.91 L 0.852 e
Page 161 and 162: Turn Lanes CMF = 1 - 0.7 P lt/d 0.0
Page 163 and 164: Turn Lanes occurred within 250 feet
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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