Safety Prediction Methodology and Analysis Tool for Freeways and Interchanges (2021) / Chapter Skim
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Pages 57-68
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57 CHAPTER 3: FRAMEWORK FOR SAFETY PREDICTION This chapter describes a framework for freeway and interchange safety prediction. The framework includes the SPFs and CMFs.
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58 Figure 36. HSM predictive method.
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59 Scalable Evaluation. The predictive method is scalable such that it can be used to evaluate an individual site or a facility.
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60 alignment. Ramp terminal configuration influences are likely to be sensitive to intersection control mode, number of legs, and turn movement accommodation.
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61 ● freeway speed-change lane. The SPF and CMF identification process was intentionally broad to ensure that a wide range of safety influences were fairly considered.
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62 ● Importance: weight = 3 ○ high = 3, medium = 2, and low = 1. ● Level of effort: weight = 2 ○ high = 1, medium = 2, and low = 3.
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63 TABLE 7. Prioritized list of SPFs and CMFs for freeway segments Category Topic 1 Importa nce Level of Effort Number Attrib.
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64 The "clear zone width" listed in Table 7 is specific to vertical objects in the clear zone, and does not include non-traversable slopes. This limitation reflects the type of information that can be discerned from aerial photographs (which was the primary source of supplemental data for this project, as described in Chapter 4)
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65 TABLE 8. Prioritized list of SPFs and CMFs for interchange ramp Category Topic 1 Importa nce Level of Effort Number Attrib.
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66 Table 9 identifies the prioritized list of SPFs and CMFs for crossroad ramp terminals. The proposed priority associated with each SPF or CMF topic is shown in the last column.
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67 The findings from the review of the literature and several state DOT databases indicated that only about 1 percent of all interchanges have the SPUI form. Thus, the challenge to developing an SPF for the SPUI is to find a sufficient number of these interchanges to quantify statistically valid relationships.
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68 predictive methods for intersections and segments. However, unlike intersection-related crashes, speed-change-related crashes are difficult to accurately identify using the attributes provided in highway crash databases.
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