Synthesis of Safety for Traffic Operations - Transports Canada

More documents

Recommendations

Info

Synthesis of Safety for Traffic Operations March 2003 Intersections that were selected for analysis were intersections that had already been reconstructed with left-turn lanes. No information is provided on the site selection criteria, but it is assumed that these sites “warranted” the turn lanes. Again, this method of site selection limits the applicability of the results to those intersections that warrant left-turn lanes. Thomas and Smith (2001) Thomas and Smith (2001) undertook an examination of the safety impacts of providing exclusive turning lanes at 8 intersections in Iowa. The site selection process is not described; the study methodology is a naïve before-after analysis using crash frequency and severity. The crash frequency is comprised of three years of before and three years of after data categorized by severity, and several impact types. The results are shown in Table 9.7, some outliers have been removed from the dataset. TABLE 9.7: CMFs for Adding Exclusive Turn Lanes (Thomas and Smith) Crash Type Mean # Sites 90% Confidence Intervals Lower Upper Fatal 0.00 1 N/A N/A Major 1.40 5 3.86 Severity Minor 1.96 7 3.28 0.65 Possible 1.05 7 1.28 0.82 PDO 0.77 6 0.91 0.62 Right-angle 1.40 7 2.19 0.61 Impact Type Rear-end 0.78 7 1.06 0.49 Left-turn 2.27 7 3.61 0.92 Other 0.69 7 0.87 0.60 Total 0.88 7 1.12 0.64 The results indicate that under a 90% degree of confidence, safety benefits can be expected for total crashes. The aetiology supports the apparent increase in crash severity, as the exclusive turn lanes might be expected to increase the overall speed travelled through the intersection. It is surprising, and perhaps counterintuitive, to see that left-turn crashes actually increase (CMF=2.27) by the addition of left-turn lanes. Region of Waterloo (2001) As part of an ongoing program the Region of Waterloo, Ontario routinely assesses the street system for locations with an elevated risk for motor vehicle crashes, and implements appropriate countermeasures. The Region of Waterloo (2001) reports that in Page 113
Turn Lanes 1998 one of their high crash locations was modified to include a left and right turn lane on one of the intersection approaches. Crashes were reduced from nine to four, for a CMF of 0.44. While impressive, the Waterloo analysis is a naïve before-after study of crash frequency using one-year of before and one year of after data. Furthermore, the countermeasure was implemented, at least in part, because this location had an aberrant crash record. The results are very unreliable due to a failure to account regression-to-the-mean, the limited sample size, and the failure to account for exposure. Harwood et al (2002) In a comprehensive analysis of the safety impacts of left- and right-turn lanes, Harwood et al (2002) conducted before-after studies for intersection improvements in eight states. A total of 280 sites were treated and 300 sites were used as comparison or reference sites. The sites were in urban and rural settings and were either two-way stop controlled, or signalized (i.e., all-way stop controlled sites were excluded from the analysis). All sites has either three or four approaches; all approaches were public streets (i.e., no private driveways were included in the sites). The Harwood et al study employed three different evaluation methods: the matched-pair approach, the before-after evaluation with a comparison group, and the before-after study using Empirical Bayes methods. Crashes that were included in the analysis are those that occurred within 250 feet of the intersection, and were coded as intersection-related. Before and after time periods varied between one and 10 years, with averages of 6.7 years and 3.9 years, for the before and after periods, respectively. The results of the analysis and the recommendations of the researchers are shown in Table 9.8. TABLE 9.8: Safety Impacts of Left-turn Lanes on Major Road Approaches No. of Approaches on which Intersection Type Setting Traffic Control Left-turn Lanes are added One Two Three-leg Rural STOP control 0.56 -- Signal 0.85 -- Urban STOP control 0.67 -- Signal 0.93 -- Four-leg Rural STOP control 0.72 0.52 Signal 0.82 0.67 Urban STOP control 0.73 0.53 Signal 0.90 0.81 Page 114
Page 1 and 2:
Transport Canada Transports Canada
Page 4:
Synthesis Of Safety For Traffic Ope
Page 8 and 9:
DISCLAIMER The material presented h
Page 10 and 11:
EXECUTIVE SUMMARY Traffic operation
Page 12 and 13:
Synthesis of Safety for Traffic Ope
Page 14 and 15:
Page 16 and 17:
TABLE OF CONTENTS DISCLAIMER REJET
Page 18 and 19:
Page 20 and 21:
LIST OF TABLES TABLE 3.1: Crash Rat
Page 22 and 23:
Page 24:
Chapter 1: Chapter 1: Introductio I
Page 27 and 28:
Introduction Before proceeding, a f
Page 29 and 30:
Introduction Literature regarding t
Page 31 and 32:
Introduction The current science of
Page 33 and 34:
Introduction adequate size control
Page 35 and 36:
Introduction In concluding this sec
Page 38 and 39:
Page 40 and 41:
Page 42:
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
Page 49 and 50:
Intersection Control Vancouver Regi
Page 51 and 52:
Intersection Control V m = the sum
Page 53 and 54:
Intersection Control where: X1 = 0
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
Page 61 and 62:
Page 63 and 64:
Intersection Control program includ
Page 65 and 66:
Intersection Control TABLE 3.26: Me
Page 67 and 68:
Intersection Control TABLE 3.29: St
Page 69 and 70:
Intersection Control TABLE 3.32: Ni
Page 71 and 72:
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 87 and 88:
Page 89 and 90:
Intersection Control TABLE 3.56: Sa
Page 92 and 93:
Page 94 and 95:
Page 96 and 97:
Page 98 and 99:
Page 100 and 101:
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
Page 114 and 115: Synthesis of Safety for Traffic Ope
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: Turn Lanes Vogt determined that a l
Page 157 and 158: Turn Lanes Section TABLE 9.10: Safe
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
Page 204 and 205:
Page 206 and 207:
Page 208 and 209:
Page 210 and 211:
Page 212 and 213:
Page 214 and 215:
Page 216 and 217:
Page 218 and 219:
Page 220:
References References
Page 223 and 224:
References Bloch SA (1998) “Compa
Page 225 and 226:
References Hamilton Associates (199
Page 227 and 228:
References Lee JT, Maleck TL, and T
Page 229 and 230:
References Polanis SF (1998) “Do
Page 231 and 232:
References Vancouver, City of (1999
Page 233 and 234:
References THIS PAGE IS INTENTIONAL
Page 236 and 237:
Page 238 and 239:
Page 240 and 241:
Page 242:
Appendix B: Critical R Appendix B:
Page 245 and 246:
Critical Reviews Worksheet for Eval
Page 247 and 248:
Critical Reviews 2. Are the expecte
Page 250 and 251:
Page 252 and 253:
Page 254 and 255:
Page 256 and 257:
Page 258:
Appendix D: Appendix D: How to Use
Page 261 and 262:
How to Use Safety Performance Funct
Page 263 and 264:
How to Use Safety Performance Funct
show all

Synthesis of Safety for Traffic Operations - Transports Canada

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?