Use and Modification of Default SPFs in the IHSDM

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: IHSDM.Support@fhwa.dot.gov; (202)-493-3407

To download IHSDM software: www.ihsdm.org

Shyuan-Ren (Clayton) ChenClayton.Chen@fhwa.dot.gov; (202)-493-3054