Methodology to Predict the Safety Performance of Urban and Suburban Arterials (2008) / Chapter Skim
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Pages 122-131
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From page 122... ...
119 CHAPTER 6. ACCIDENT MODIFICATION FACTORS This chapter presents the accident modification factors (AMFs)
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From page 123... ...
120 • Based on the review and discussion at the meeting, the expert panel reached consensus and selected one or more studies as providing the most credible AMF, which was recommended for potential use in the HSM. Criteria considered by the expert panel in assessing studies as potential sources of AMFs included quality of documentation; sample size; study design, including compensation for regression to the mean; and standard error or goodness of fit.
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From page 124... ...
121 Pb/0 = for that part of the street with parking, the proportion that has business or office as adjacent land use fap/pp = ratio of crashes on streets with angle parking to crashes on streets with parallel parking Pap = for that part of the street with parking, the proportion with angle parking Bonneson has derived the value of 2.34 for fap/pp. Based on Equation (37)
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From page 125... ...
122 TABLE 60. Determination of the accident modification factor for on-street parking for specific types of roadway segments Roadway cross section Land use Type of parking Ics Pb/0 fap/pp Pap fpka Ppk AMF1rb Multilane Residential Parallel 0 0.0 2.34 0.0 1.100 1.0 1.00 Commercial/industrial Parallel 0 1.0 2.34 0.0 1.709 1.0 1.709 Two-lane Residential Parallel 1 0.0 2.34 0.0 1.465 1.0 1.465 Commercial/industrial Parallel 1 1.0 2.34 0.0 2.074 1.0 2.074 Multilane Residential Angle 0 0.0 2.34 1.0 2.574 1.0 2.574 Commercial/industrial Angle 0 1.0 2.34 1.0 3.999 1.0 3.999 Two-lane Residential Angle 1 0.0 2.34 1.0 3.428 1.0 3.428 Commercial/industrial Angle 1 1.0 2.34 1.0 4.853 1.0 4.853 a Determined with Equation (37)
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From page 126... ...
123 Figure 23. Relationships of fixed-object collisions to fixed-object density and offset [adapted from Zegeer and Cynecki (130)
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124 accidents, which constitute the proportion of total accidents (excluding vehicle-pedestrian and vehicle-bicycle collisions) shown in Table 62.
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From page 128... ...
125 Accident severity level Best estimate of nighttime accident reduction Fatal 64% Injury 28% Property-damage-only 17% Table 63 illustrates the derivation of an AMF for total accidents based on these estimates using crash distribution data for Minnesota and Michigan combined. The AMFs for the individual road types are so similar that a single combined AMF of 0.96 for all road types seems appropriate.
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From page 129... ...
126 INTERSECTIONS Recommended AMFs for intersections presented below include: • left-turn lanes • left-turn signal phasing • right-turn lanes • right turn on red • lighting The expert panel recommended the inclusion of all of these AMFs. The inclusion of an AMF for red-light cameras was designated as optional.
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From page 130... ...
127 TABLE 64. AMFs for left-turn signal phasing Original left-turn phasing Modified left-turn phasing Accident type AMF for specific accident type Proportion of specified accident type AMF for total accidents (AMF2i)
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From page 131... ...
128 portion of the safety benefit represented by Equation (42) was due to reduction of collisions between right-turning vehicles and pedestrians, but that the proportion was so small that the value 0.984 did not change (i.e., the effect was in the fourth significant digit)
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