Synthesis of Safety for Traffic Operations - Transports Canada

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Synthesis of Safety for Traffic Operations March 2003 were fairly constant over time. The overall conclusion was that the improved delineation increased night-time driving speeds as follows: • PMDs produced a 2.0 to 2.5 ft/s increase • RPMs produced a 1.0 ft/s increase • Chevrons produced a 0.5 ft/s decrease at sites in Georgia, and a 3 ft/s increase at sites in New Mexico In all cases the night-time speeds were noted as being below the daytime speeds. Lalani (1991) The City of San Buenaventura, California as part of a Comprehensive Safety Program installed chevron signs at three locations (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., is the curve in an urban or rural location? What are the geometrics of the curves?). The results are shown in Table 4.5. TABLE 4.5: Safety Impacts of Chevron Signs in San Buenaventura, California Location Crashes Before After CMF A 8 4 0.50 B 3 0 0.00 C 3 0 0.00 Totals 14 4 0.29 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. Land Transport Safety Authority of New Zealand (1996) The safety impact of chevron warning signs at horizontal curves was investigated by the Land Transport Safety Authority of New Zealand (1996). It is not specifically stated, although it is implied that the locations selected for treatment were curves that were experiencing a higher than usual number of collisions. A total of 103 sites were included in the analysis, 83 in rural areas (i.e., a speed limit in excess of 70 km/h), and 20 in urban areas (i.e., a speed limit of 70 km/h or less). Page 65
Traffic Signs Only nine of the sites were treated with chevrons only, the remaining sites had complementary improvements including raised pavement markings, post mounted delineators, new or relocated traffic signs, pavement markings, etc. The evaluation methodology was a before-after analysis with some control for overall crash trends. The report indicates that an “expected” number of crashes is calculated by adjusting the “before” data with local crash trends. It is not specifically stated how this was done. The average “before” period for collision data was 5.3 years; the average “after” period was 3.1 years. The analysis yielded the CMFs shown in Table 4.6. TABLE 4.6: Safety Impacts of Chevron Signs in New Zealand CMF Crash Type Urban Open Road Area All 0.52 0.46 Lost Control 0.57 0.38 Head-on 0.24 0.31 Day 0.63 0.55 Night 0.33 0.33 Twilight 0.79 0.73 Fatal 0.30 0.33 Serious 0.26 0.48 Minor 0.77 0.45 All sites combined yielded a CMF of 0.51. Statistical testing establishes 95% confidence intervals of 0.70 to 0.32. Tribbett et al (2000) The California Department of Transportation investigated the safety effectiveness of dynamic curve warning sign systems at five locations. The treatment was the erection of a changeable message sign (CMS) that is connected to a radar speed-measuring device, and detection equipment. The CMSs were 10 feet wide by seven feet high and are full matrix light-emitting diodes. The message to be displays varies but is generally related to either the advisory speed of the downstream curve, or the operating speed of the approaching vehicle. The study methodology is a naïve before-after analysis of crash frequency. Crashes that occurred from the (proposed) CMS location to one-tenth of a mile downstream of the end of the curve were included in the analysis. The evaluation was undertaken about seven months after sign installation, so the “after” data period is very short. To account for seasonal variations in crash data, the available five years of “before” data was culled to Page 66
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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
Page 45 and 46: Intersection Control TABLE 3.3: Cra
Page 47 and 48: Intersection Control TABLE 3.5: CMF
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Page 51 and 52: Intersection Control V m = the sum
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Page 55 and 56: Intersection Control Region of Durh
Page 57 and 58: Intersection Control TABLE 3.17: CM
Page 59 and 60: Intersection Control The predictor
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Page 67 and 68: Intersection Control TABLE 3.29: St
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Page 73 and 74: Intersection Control It is noted th
Page 75 and 76: Intersection Control Sayed et al (1
Page 77 and 78: Intersection Control Signal Clearan
Page 79 and 80: Intersection Control The CMFs are 0
Page 81 and 82: Intersection Control also examined
Page 83 and 84: Intersection Control Shebeeb (1995)
Page 85 and 86: Intersection Control approaches at
Page 89 and 90: Intersection Control TABLE 3.56: Sa
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Page 102: 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 127 and 128: Bicycle Safety TABLE 7.1: Safety Im
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Chapter 9: Chapter 9: Turn Lanes Tu
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Turn Lanes TABLE 9.2: Safety Impact
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Turn Lanes Vogt determined that a l
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Turn Lanes 1998 one of their high c
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Turn Lanes Section TABLE 9.10: Safe
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Turn Lanes A T = ADT 0.91 L 0.852 e
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Turn Lanes CMF = 1 - 0.7 P lt/d 0.0
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Turn Lanes occurred within 250 feet
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TABLE 10.3: Speed Changes Resulting
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Sites Where Applied 1 URBAN Island
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Forbes and Gill (2000) undertook a
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Ideally, three years of before and
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Kermit and Hein (1962) looked into
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The effects of the transverse pavem
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Chapter 11: Chapter 11: Other Other
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Other Safety Issues collisions per
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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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