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Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst

Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst. Doug Harwood Midwest Research Institute. Purpose of Calibration. To enable SPFs or safety prediction methods developed with data from one jurisdiction to be applied in another jurisdiction.

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Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst

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  1. Calibration of SPFs in the HSM, IHSDM, and SafetyAnalyst Doug Harwood Midwest Research Institute

  2. Purpose of Calibration To enable SPFs or safety prediction methods developed with data from one jurisdiction to be applied in another jurisdiction

  3. What Differences Between Jurisdictions Does Calibration Account For? Climate Driver behavior Animal populations Crash reporting thresholds Crash reporting system procedures

  4. How is the Calibration Factor Used? Typical SPF with Calibration Factor: N = exp(a + b x ln( AADT)) C

  5. How is the Value of the Calibration Factor Determined? Steps in Calibration: Select facility types and SPFs Select calibration sites Obtain data: site characteristics observed crash data Apply SPF or predictive method to each site Compute calibration factor

  6. How is the Value of the Calibration Factor Determined? C = Sum of observed crashes Sum of predicted crashes

  7. 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

  8. How is the Calibration Factor Used? SafetyAnalyst SPF with calibration factor: N = exp(a + b x ln( AADT)) C

  9. Data Needs for Calibration of SafetyAnalyst Site characteristics Crash frequencies All needed data are mandatory variables in the SafetyAnalyst data set

  10. Calibration in HSM Part C The entire predictive method for a given facility type is calibrated, rather than individual SPFs

  11. 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

  12. 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

  13. 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

  14. Questions?

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