Accident Modification Factors for Traffic Engineering and ITS Improvements (2008) / Chapter Skim
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AMF Summaries
AMF Summaries
Pages 34-67
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From page 34... ...
In some cases, the AMF was developed through further analysis by one of the NCHRP project research teams sponsoring the expert panel meeting. • Cross-Sectional Model.
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From page 35... ...
Signal Heads with 12-in. Signal Heads Reanalysis of Existing/Supplemental Data Replace Single Red Signal Head with Dual Red Signal Heads Reanalysis of Existing/Supplemental Data Convert Nighttime Flash Operation to Steady Operation Reanalysis of Existing/Supplemental Data Convert to All-Way Stop Control Literature Review Convert Stop Control to Yield Control Literature Review Install Red-Light Cameras Literature Review Add Intersection Lighting Expert Panel Increase Pavement Friction on Intersection Approach Reanalysis of Existing Data Roadway Segment Treatments Narrow Lane Widths to Add Lanes Literature Review Add Passing Lanes (Two-Lane Roads)
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From page 36... ...
• The authors were not able to determine the safety effects for pedestrians and bicyclists, but refer the reader to the positive results that have been found in Scandinavian evaluations.A • No evidence was found to indicate roundabouts result in more difficulties for older drivers. CRASH TYPE STUDIED AND ESTIMATED EFFECTS AMF Level of Predictive Certainty: High AMF 0.44 (0.06)
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CRASH TYPE STUDIED AND ESTIMATED EFFECTS AMF Level of Predictive Certainty: High* Fatal and Injury Intersection Accidents (all accident types)
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0.91C -- Urban Stop-Controlled Intersection (four legs) 0.77C 0.59C CRASH TYPE STUDIED AND ESTIMATED EFFECTS AMF Level of Predictive Certainty: High*
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From page 39... ...
. • An additional reference group was developed from the HSIS California urban data and included 1,418 stop-controlled and 799 signalized intersections.A • Minor street traffic volumes for the treatment sites ranged from 911 to 3,952 vpd; major street volumes ranged from 11,739 to 24,584 vpd.
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0.4 (0.05) AMF Level of Predictive Certainty: High CRASH TYPE STUDIED AND ESTIMATED EFFECTS ECONOMIC ANALYSI S Three-Leg and Four-Leg Intersections Combined N o.
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From page 41... ...
199 0.78 0.70 0.47 (0.10) CRASH TYPE STUDIED AND ESTIMATED EFFECTS AMF Level of Predictive Certainty: High STUDY SITES: • 199 treatment sites and 71comparison sites in Philadelphia.
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. ACCIDENT MODIFICATION FUNCTION AMF Level of Predictive Certainty: Medium-High FOOTNOTES: A Clark, Maghsoodloo, and Brown - 1983 (79 )
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12 0.99A (0.07) AMF Level of Predictive Certainty: Medium-High CRASH TYPE STUDIED AND ESTIMATED EFFECTS REFERENCE: NCHRP Project 17-25 research results Accident Type No.
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. AMF Level of Predictive Certainty: Medium-High CRASH TYPE STUDIED AND ESTIMATED EFFECTS REFERENCE: NCHRP Project 17-25 research results Accident Type No.
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0.65B (0.15) TREATMENT: Replace Single Red Signal Head with Dual Red Signal Heads METHODOLOGY: Empirical Bayes Before-After Right-Angle All AMF Level of Predictive Certainty: Medium-High CRASH TYPE STUDIED AND ESTIMATED EFFECTS COMMENTS: • Adding additional signal heads does not seem to be effective in reducing right-angle or total crashes.
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0.53 0.29 (0.06) 360A CRASH TYPE STUDIED AND ESTIMATED EFFECTS AMF Level of Predictive Certainty: Medium-High STUDY SITES: • Included data from three urban regions (San Francisco, Philadelphia, and Toronto)
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CRASH TYPE STUDIED AND ESTIMATED EFFECTS AMF Level of Predictive Certainty: Medium-High AMF 2.37 Total Accidents (all severities)
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of Treated Sites AMF Level of Predictive Certainty: High AMF ECONOMIC ANALYSIS Economic AMF CRASH TYPE STUDIED AND ESTIMATED EFFECTS 1.15 (0.03)
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of Treated Sites AMF Level of Predictive Certainty: High CRASH TYPE STUDIED AND ESTIMATED EFFECTS FOOTNOTES: A Bray - 2001 ( 80 )
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Two-way (short four-lane sections) CRASH TYPE STUDIED AND ESTIMATED EFFECTS AMF Level of Predictive Certainty: Medium-High Type of Passing Lane REFERENCE: Harwood et al.
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Thus, the AMF shown here is applicable to rural and urban two-lane and multilane roads. • NCHRP Project 17-25 urban/suburban expert panel confirmed the adoption of this AMF for the road classes noted above.
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. B Related accidents include single-vehicle run-off-road, multiple-vehicle head-on, and opposing- and same-direction sideswipe accidents.
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- 2003 (51) AMFTRA = accident modification factor for related accidents based on shoulder typeB AMFTRA is calculated by dividing the AMF for the after-improvement condition by the AMF for the before condition - each can be selected from the following table: ACCIDENT MODIFICATION FUNCTION COMMENTS: • Shoulder width AMFs for ADTs greater than 2,000 are largely based on work by Zegeer et al.
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1.06 + 3(SD - 0.02) < 0.01 0.01 < SD < 0.02 > 0.02 AMF Level of Predictive Certainty: Medium-High AMFSuperelevation Deficiency (SD)
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No. of Improved Sites AMF CRASH TYPE STUDIED AND ESTIMATED EFFECTS 0.79 (0.10)
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CRASH TYPE STUDIED AND ESTIMATED EFFECTS 0.85 (0.08) 98 REFERENCE: Persaud, Retting, and Lyon - 2003 (57 )
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Therefore, they are not included here. Run-Off-Road Accidents AMF 0.56 (0.10)
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AADT after conversion ranged from 6,194 to 26,376. AMF Level of Predictive Certainty: High CRASH TYPE STUDIED AND ESTIMATED EFFECT No.
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• Sites are selected for treatment based on both a high proportion of wet- road accidents and low friction numbers. CRASH TYPE STUDIED AND ESTIMATED EFFECTS 36 miles Rear-End Wet-Road Crashes COMMENTS: • The treatment generally involved a 1.5-in.
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From page 63... ...
• Over the 10-year period, the partial/no-access control sections experienced approximately 41,000 total crashes and 5,000 cross-median crashes. The full-access control sections experienced approximately 125,000 total crashes and 5,000 cross-median crashes.
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From page 64... ...
. AMF Level of Predictive Certainty: Medium-High REFERENCES: NCHRP Project 17-25 research results ACCIDENT MODIFICATION FACTORS COMMENTS: • Original study conducted by Zegeer et al.
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From page 65... ...
P b/ o = proportion of street with parking that has business or office as adjacent land use f ap/pp = ratio of crashes on streets with angle parking to crashes on streets with parallel parking (= 2.34; see comment) P ap = for that part of the street with parking, the proportion of the street with angle parkin g COMMENTS: • Expert panel on urban/suburban arterials considered this AMF function to be the best estimate for the addition or removal of on-street parking.
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From page 66... ...
No. of Median Sites 173 CRASH TYPE STUDIED AND ESTIMATED EFFECTS TREATMENT: Add Roadway Segment Lighting METHODOLOGY: Meta-analysis/Expert Panel Total Crashes All Injury Crashes Total Crashes All Injury Crashes CRASH TYPE STUDIED AND ESTIMATED EFFECTS AMF Level of Predictive Certainty: Medium-High REFERENCE: Elvik and Vaa - 2004 (60 )
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From page 67... ...
Each result contained information on mean speed and crash frequency before treatment and mean speed and crash frequency after treatment. A • The NCHRP Projects 17-25/17-26 expert panel reviewed the original study and requested supplemental analysis to explore the validity of the results and to develop AMFs.
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