Use and Modification of Default SPFs in the
IHSDM
Mike DimaiutaLENDIS Corporation
Options for using SPFs in IHSDM
• Use Default SPFs “as is”• Calibrate models, including SPFs• Enter and use “your own” SPFs
Use Default SPFs “as is”
• Run IHSDM Crash Prediction Module (CPM) without calibrating (i.e. with calibration factors = 1.0)
Use Default SPFs
Use Default SPFs “as is”
Calibrate Models / SPFs
• Follow HSM Part C calibration procedure and enter factors via IHSDM Administration Tool
Calibrate Models / SPFs
Calibrate Models / SPFs
Calibrate model / SPFs
Calibrate model / SPFs
Enter and use “your own” SPFs
• Via the IHSDM Administration Tool:– “Crash Prediction” >• “Model Data Sets”
Enter and use “your own” SPFs
• Capabilities:– For all SPFs, can change:• Regression coefficients• Overdispersion parameters
• Limitation:– Can not change SPF functional form
Enter and use “your own” SPFs
• After editing data, save as a new Model Data Set “configuration” and select when running CPM
Enter and use “your own” SPFs
• Example: Multilane Rural H’way– Estimate crashes using defaults– Enter “My State’s SPFs” into
Administration Tool– Run CPM with modified SPFs to
generate and compare results
Estimate crashes using default SPFs
Enter “My State’s” SPFs into Administration Tool
Enter “My State’s” SPFs into Administration Tool
Enter “My State’s” SPFs into Administration Tool
Run CPM with modified SPFs
Compare Results
• Estimated Total crashes using default SPFs: 27.84
• Estimated Total crashes using “My State’s” SPFs: 27.62
Summary
• No requirement for agencies to develop their own SPFs for IHSDM, but…
• IHSDM provides a mechanism for agencies to edit all default SPFs (coefficients and overdispersion parameters only)
• Either way can produce good results!
Questions?
For additional information:www.tfhrc.gov/safety/ihsdm/ihsdm.htm
IHSDM Technical Support: [email protected]; (202)-493-3407
To download IHSDM software: www.ihsdm.org
Shyuan-Ren (Clayton) [email protected]; (202)-493-3054
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