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Development and Use of Iowa's SPF Models for Traffic Safety Analysis

Learn about the development and use of Iowa's Safety Performance Function (SPF) models for evaluating and predicting the effectiveness of countermeasures in improving traffic safety. Discover the various examples of SPF use and the ongoing studies in Iowa. Gain insights into the methodological approach and the importance of data improvement for accurate SPF estimation.

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Development and Use of Iowa's SPF Models for Traffic Safety Analysis

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  1. Session 9:Local SPF Use- Iowa Michael Pawlovich, Ph.D., P.E. Iowa Dept. of Trans., Traffic and Safety

  2. Iowa “SPF” Development • Don’t really use “SPF”s, per se, currently – do use CRFs/AMFs • Have developed models, mostly for evaluation of past countermeasures • Don’t use EB… • went from classical  FB • essentially same difference but Iowa resources allowed • development continues

  3. Iowa “SPF” Examples • Examples of Iowa FB use: • Bayesian Intersection Ranking (past) • limited # of sites • demonstration case • 4  3-lane Before/After Evaluation Study (past and published) • could use as an SPF but haven’t had need • 2  3-lane Before/After Evaluation Study (ongoing) July 29 and 30, 2009 3

  4. Iowa “SPF” Examples • More examples of Iowa FB use: • Impacts of Bypasses Before/After Evaluation Study (ongoing) • Bayesian SICL (network screening) – intersection and segment (1st ongoing, 2nd future) • Comparables/Expected Values (future) • Alternate considerations for location – not site-based but crash-based (future) July 29 and 30, 2009 4

  5. Iowa SPF Thoughts • Methodologically, we can develop prediction models or SPFs • begin from engr. problem and site data • develop stat. models faithful to engr. concepts and include parameters interpretable in the engineering context • Model parameters estimated using fully Bayesian (hierarchical) methods July 29 and 30, 2009 5

  6. Iowa SPF Thoughts • We are trying to develop models/SPFs useable over a reasonably wide range of site types • base estimates on datasets with a diversity of site attributes • model over these diverse attributes July 29 and 30, 2009 6

  7. Iowa SPF Thoughts For example, if we wish to investigate one type of site vs. another we can use the same SPF as long as the data and model properly contain the means Limitation not software or stat. tools but rather that needed data not available to permit estimating canonical SPFs – working towards July 29 and 30, 2009 7

  8. Conclusion • Data improvement crucial • canonical SPFs • specific SPFs • analyses in general • Learning and improving as we go • "If we knew what it was we were doing, it would not be called research, would it?“ - Albert Einstein July 29 and 30, 2009 8

  9. Thank youmichael.pawlovich@dot.iowa.gov

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