Synthesis of Safety for Traffic Operations - Transports Canada

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Synthesis of Safety for Traffic Operations March 2003 settings, and were targeted for operational improvements. The models that were developed were for intersection approaches; therefore the crashes at each intersection were assigned to a specific approach. The models were developed using negative binomial regression, which is appropriate for modelling sparse, non-negative integers such as motor vehicle crashes. A total of 64 variables (intersection characteristics) were analysed. Four separate models were developed for all, rear-end, angle, and approach-turn crashes. The model for all crashes is shown in Equation 3.1. N all = 0.244 exp(0.251V lt + 0.0902V rt + 0.0523V o +0.153L) * exp(–0.753TC –0.325TS + 0.27P 2 +0.61P 8 –0.468PL) * exp(–0.336LS –1.093AL +1.123SD +0.201TL –0.899LA) * exp(0.0203SL – 0.0075SL o ) [3.1] where: N all = Annual number of crashes on the intersection approach V lt = Average daily left-turn volume in thousands V rt = Average daily right-turn volume in thousands V o = Average daily total opposing traffic volume in thousands L = Number of through, combined through-right, and right-turn lanes TC = Traffic control on approach (1 if no control; 0 otherwise) TS = Signal control on approach (1 is signalized; 0 otherwise) P 2 = Two-phase signal (1 is two-phase; 0 otherwise) P 8 = Eight-phase signal (1 if eight-phase; 0 otherwise) PL = Protected left-turn (1 if protected; 0 otherwise) LS = Local street approach (1 if local street; 0 otherwise) AL = All approaches are local streets (1 if all local; 0 otherwise) SD = Sight-distance restrictions (1 is restricted; 0 otherwise) TL = 1 if there is a combined through-left lane and two or more lanes on the approach; 0 otherwise LA = 1 if left-turns are not aligned and the approach does not have a single lane, protected left, or stop control; 0 otherwise SL = Approach speed limit (km/h) SL o = Opposing approach speed limit (km/h) The model provides some noteworthy results with respect to traffic operations and control strategies. Firstly, in using an uncontrolled approach as the base condition, it can be estimated that a change in intersection control would be associated with an increase in crash frequency on that approach according to the CMFs shown in Table 3.5. Page 17
Intersection Control TABLE 3.5: CMFs for a Change in Approach Control Approach Control CMF Uncontrolled 1.00 Stop-control 2.12 Traffic signal Two-phase 2.01 Eight-phase 1.77 The above results are consistent with intuition. In applying the above CMFs to a twoway stop controlled intersection with four approaches, signalization would decrease crash occurrence on the two stop-controlled approaches, and increase crashes on the two uncontrolled approaches. Furthermore, the results indicate that modifying signal operation from two-phases to eight-phases is a safety benefit. The Poch and Mannering analysis selected intersections that were identified for operational improvements. This limits the applicability of the model and the CMFs to intersections that are considered to be operationally deficient and requiring remedial work. In this instance, remedial work consisted of intersection reconstruction that improves the intersection, modifying intersection control, modifying the signal timing/phasing at signalized locations, and/or providing channelization. Tople (1998) Tople (1998) in an evaluation of hazard elimination and safety projects included a review of the safety benefits of signalization at nine locations in South Dakota. 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 were used in the analysis. The results of the analysis are presented in Table 3.6. TABLE 3.6: Safety Impacts of Signalization in South Dakota No. Crashes EPDO Crashes* Improvement AADT of Type Range Before After CMF Before After CMF Sites 5960 - Signal 9 188 139 0.74 2313 2307.5 1.00 20995 * EPDO crashes were calculated as (1300*F)+(90*I)+(18*N)+(9.5*P)+PDO where: F = fatal crash I = incapacitating injury crash N = non-incapacitating injury crash P = possible injury crash PDO = Property damage only crash Page 18
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 16 and 17: TABLE OF CONTENTS DISCLAIMER REJET
Page 20 and 21: LIST OF TABLES TABLE 3.1: Crash Rat
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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
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Page 45: Intersection Control TABLE 3.3: Cra
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
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Page 73 and 74: Intersection Control It is noted th
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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)
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Synthesis of Safety for Traffic Ope
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Chapter 5: Chapter 5: Pavement Pave
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Pavement Markings The study methodo
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Pavement Markings Hall (1987) Hall
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Pavement Markings TABLE 5.8: Safety
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Pavement Markings THIS PAGE IS INTE
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Chapter 7: Chapter 7: Bicycle Bicyc
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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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