Understanding and Communicating Reliability of Crash Prediction Models (2021) / Chapter Skim
Currently Skimming:
Pages 62-72
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 62... ...
60 Chapter 6. Reliability Associated with Using a CPM to Estimate Frequency of Rare Crash Types and Severities: Overview of the Problem with Possible Solutions Introduction In the 1st edition of the HSM (AASHTO, 2010)
|
From page 63... ...
61 Figure 3. Crash Type and Severity SPFs for Signalized Intersections that could not be estimated in NCHRP Project 17-62 Figure 4.
|
From page 64... ...
62 Method to Assess Potential Reliability This Chapter addresses the reliability of predictions obtained from the simple two-stage approach as it applies to rare crash types for which three cases may prevail. The three cases are as follows: ο· Case A: Models did not converge or were illogical (e.g., AADT exponents were negative or statistically insignificant at the 10% level)
|
From page 65... ...
63 Coefficient of Variation of Calibration Factor (Defined As CV) The CV of the calibration factor is the standard deviation of the calibration factor divided by the estimate of the calibration factor as shown in the following equation.
|
From page 66... ...
64 The Illinois validation dataset is used in this illustration for estimating the crash type/severity proportion as well as for assessing the resulting SPF when the proportion is applied to the parent SPF from California estimation data. The eight crashes in the Illinois dataset constituted 17.02% of all SD crashes and 38.01% of all KA crashes in the Illinois validation dataset.
|
From page 67... ...
65 Β Figure 5. FHWA Calibrator Tool CURE plot of residuals based on modified NCHRP Project 17-62 estimated base condition SPF (Option 1, Equation 55)
|
From page 68... ...
66 Β Figure 6. FHWA Calibrator Tool CURE plot of residuals based on modified NCHRP Project 17-62 estimated base condition SPF (Option 2, Equation 56)
|
From page 69... ...
67 Equation 57 πΆπππ βππ π¦πππ exp 9.502 πππ‘ππ πΈππ‘πππππ π΄π΄π·π . The SPF was estimated based on only 12 crashes at 139 sites in Minnesota and the large standard error for the AADT exponent (0.558)
|
From page 70... ...
68 Figure 7. Calibrator CURE plot of residuals based on original NCHRP Project 17-62 estimated base condition SPF (Equation 57)
|
From page 71... ...
69 Figure 8. Calibrator CURE plot of residuals based on modified NCHRP Project 17-62 estimated base condition SPF (Option 1, Equation 58)
|
From page 72... ...
70 Figure 9. Calibrator CURE plot of residuals based on modified NCHRP Project 17-62 estimated base condition SPF (Option 2, Equation 59)
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.