Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst Doug Harwood Midwest Research Institute.
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Transcript of Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst Doug Harwood Midwest Research Institute.
![Page 1: Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst Doug Harwood Midwest Research Institute.](https://reader034.fdocuments.us/reader034/viewer/2022051316/5697bfe21a28abf838cb43a4/html5/thumbnails/1.jpg)
Calibration of SPFs in the HSM, IHSDM, and
SafetyAnalyst
Doug HarwoodMidwest Research Institute
![Page 2: Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst Doug Harwood Midwest Research Institute.](https://reader034.fdocuments.us/reader034/viewer/2022051316/5697bfe21a28abf838cb43a4/html5/thumbnails/2.jpg)
Purpose of Calibration
• To enable SPFs or safety prediction methods developed with data from one jurisdiction to be applied in another jurisdiction
![Page 3: Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst Doug Harwood Midwest Research Institute.](https://reader034.fdocuments.us/reader034/viewer/2022051316/5697bfe21a28abf838cb43a4/html5/thumbnails/3.jpg)
What Differences Between Jurisdictions Does Calibration
Account For?
• Climate• Driver behavior• Animal populations• Crash reporting thresholds• Crash reporting system procedures
![Page 4: Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst Doug Harwood Midwest Research Institute.](https://reader034.fdocuments.us/reader034/viewer/2022051316/5697bfe21a28abf838cb43a4/html5/thumbnails/4.jpg)
How is the Calibration Factor Used?
Typical SPF with Calibration Factor:
N = exp(a + b x ln( AADT)) C
![Page 5: Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst Doug Harwood Midwest Research Institute.](https://reader034.fdocuments.us/reader034/viewer/2022051316/5697bfe21a28abf838cb43a4/html5/thumbnails/5.jpg)
How is the Value of the Calibration Factor
Determined?
Steps in Calibration:1. Select facility types and SPFs2. Select calibration sites3. Obtain data:• site characteristics• observed crash data
4. Apply SPF or predictive method to each site
5. Compute calibration factor
![Page 6: Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst Doug Harwood Midwest Research Institute.](https://reader034.fdocuments.us/reader034/viewer/2022051316/5697bfe21a28abf838cb43a4/html5/thumbnails/6.jpg)
How is the Value of the Calibration Factor
Determined?
C = Sum of observed crashes Sum of predicted crashes
![Page 7: Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst Doug Harwood Midwest Research Institute.](https://reader034.fdocuments.us/reader034/viewer/2022051316/5697bfe21a28abf838cb43a4/html5/thumbnails/7.jpg)
Calibration in SafetyAnalyst
• The SPF for each individual facility type (i.e., site subtype) is calibrated separately for each calendar year
• All available sites for each site subtype of interest are used
• Calibration is done automatically by the software whenever new data are loaded – no user intervention is required
![Page 8: Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst Doug Harwood Midwest Research Institute.](https://reader034.fdocuments.us/reader034/viewer/2022051316/5697bfe21a28abf838cb43a4/html5/thumbnails/8.jpg)
How is the Calibration Factor Used?
SafetyAnalyst SPF with calibration factor:
N = exp(a + b x ln( AADT)) C
![Page 9: Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst Doug Harwood Midwest Research Institute.](https://reader034.fdocuments.us/reader034/viewer/2022051316/5697bfe21a28abf838cb43a4/html5/thumbnails/9.jpg)
Data Needs for Calibration of SafetyAnalyst
• Site characteristics• Crash frequencies• All needed data are mandatory
variables in the SafetyAnalyst data set
![Page 10: Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst Doug Harwood Midwest Research Institute.](https://reader034.fdocuments.us/reader034/viewer/2022051316/5697bfe21a28abf838cb43a4/html5/thumbnails/10.jpg)
Calibration in HSM Part C
• The entire predictive method for a given facility type is calibrated, rather than individual SPFs
xyx2x1xx spfpredicted C)AMF...AMF(AMFN N
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Calibration in HSM Part C
• Calibration procedures are presented in the Appendix to Part C
• Guidance is provided on:– data elements needed for calibration
(listed in Exhibit A-2 in Appendix to HSM Part C)
– All input variables to HSM Part C methods are either required or desirable data
–minimum samples sizes
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Calibration in HSM Part C
• A calibration data set must be assembled for each facility type
• Minimum sample size for calibration:– 30 to 50 sites that collectively experience at
least 100 crashes per year
• The same calibration sites can be used with new crash data (and updated traffic volumes) to calibrate for future years
![Page 13: Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst Doug Harwood Midwest Research Institute.](https://reader034.fdocuments.us/reader034/viewer/2022051316/5697bfe21a28abf838cb43a4/html5/thumbnails/13.jpg)
Calibration in IHSDM
• There is no formal calibration method built into the software
• Calibration factors determined outside the software may be entered by the user
• Calibration factors developed for the HSM or SafetyAnalyst can be used in IHSDM
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Questions?