Safety Prediction Models for Six-Lane and One-Way Urban and Suburban Arterials (2022) / Chapter Skim
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Pages 88-109
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From page 88... ...
88 CHAPTER 5. PREDICTIVE MODELS FOR URBAN AND SUBURBAN ROADWAY SEGMENTS WITH SIX OR MORE LANES This chapter describes the activities undertaken to calibrate safety predictive models for urban and suburban roadway segments with six or more lanes.
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89 Figure 14. Definition of roadway segments and intersections (AASHTO, 2010)
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90 have been applied to highway crash data, they have (a) an inherent tendency to over-fit the data, (b)
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91 Table 47. Variables acquired from state databases for six-or-more-lane arterials.
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92 Table 48. Supplemental data collected for six-or-more-lane arterials.
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94 𝐼 = median barrier presence indicator variable (= 1.0 if present, 0.0 if absent)
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95 Table 49. Calibrated coefficients for FI crashes on six-or-more-lane arterials.
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96 Table 50. Calibrated coefficients for PDO crashes on six-or-more-lane arterials.
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97 The mixed nonlinear regression procedure (NLMIXED) in the Statistical Analysis System (SAS)
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98 Figure 17 and Figure 18 show the relationship between the number of PDO crashes and traffic flow for six or more lanes for multi-vehicle and single-vehicle crashes, respectively. Figure 17 shows that eight-lane divided facilities experience more multi-vehicle PDO crashes than do sixlane undivided and divided facilities.
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99 The proportions in Table 51 are used to separate multiple-vehicle crashes into components by collision type for arterials with six or more lanes. Table 51.
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100 The pedestrian crash adjustment factor is estimated by dividing the vehicle-pedestrian crashes by the total segment crashes (excluding vehicle-pedestrian and vehicle-bicycle collisions) for each segment type.
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101 𝑁 = predicted average crash frequency of an individual intersection (excluding vehicle-pedestrian and vehicle-bicycle collisions)
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102 found in the literature are typically derived from (and applied to) the combination of multiplevehicle and single-vehicle crashes.
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103 Outside Shoulder Width CMF The outside shoulder width CMF is described using Equation 161.
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104 CMF proposed in this research is compared with the CMF in HSM Chapter 12 and CMFs developed by other researchers in Figure 21. The HSM Chapter 12 CMF applies only to traversable medians without traffic barriers, not including TWLTLs.
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105 Figure 22. Median barrier CMF for multiple-vehicle crashes, six-or-more-lane arterials.
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106 Figure 23. Median barrier CMF for single-vehicle crashes, six-or-more-lane arterials.
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107 Driveway CMF The driveway CMF is applicable to multiple-vehicle crashes only. Major commercial, major industrial, and minor driveways are found to be significant in influencing crashes.
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108 The base condition for the minor driveway CMF is 10 driveways per mile. The change in CMF with the increase in the driveways is shown in Figure 26.
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109 Table 56. Roadside fixed-object CMF, six-or-more-lane arterials.
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