Examining the spatial and temporal transferability of safety performance functions: A case study for the Iowa interstate system

dc.contributor.advisor	Peter Savolainen
dc.contributor.advisor	Christopher Day
dc.contributor.author	Tian, Yu
dc.contributor.department	Civil, Construction, and Environmental Engineering
dc.date	2019-03-26T18:26:50.000
dc.date.accessioned	2020-06-30T03:14:20Z
dc.date.available	2020-06-30T03:14:20Z
dc.date.copyright	Sat Dec 01 00:00:00 UTC 2018
dc.date.embargo	2001-01-01
dc.date.issued	2018-01-01
dc.description.abstract	<p>This case study aimed to examine the spatial and temporal transferability of safety performance functions (SPFs), which were developed for the Iowa interstate system in the form of negative binomial regression models. Four years of crash data were integrated with geometric and traffic information over a four-year period for the entire interstate system. The segments were randomly split into two groups and these groups were also split into a pair of two-year time periods. This allowed for an assessment of model transferability across space, time and both dimensions. Separate models were estimated for each of the four datasets and these models were used in cross-validation exercises. The predicted values were directly compared to actual observed values to assess predictive accuracy. In this setting, less spatial variability was shown as compared to temporal variability, which was largely reflective of significant reductions in crashes that occurred over the course of the study period. In all settings, temporal transferability was relatively poor. The results improved when calibration exercises were conducted. Ultimately, the results support prior research, which suggests state-specific SPFs are recommended in order to obtain better predictive capabilities. Full models, which considered numerous predictor variables, performed better than simple models considering only annual average daily traffic. Additional research is suggested in this area in order to better understand how spatial and temporal transferability compares across different empirical settings.</p>
dc.format.mimetype	application/pdf
dc.identifier	archive/lib.dr.iastate.edu/etd/16888/
dc.identifier.articleid	7895
dc.identifier.contextkey	14007542
dc.identifier.s3bucket	isulib-bepress-aws-west
dc.identifier.submissionpath	etd/16888
dc.identifier.uri	https://dr.lib.iastate.edu/handle/20.500.12876/31071
dc.language.iso	en
dc.source.bitstream	archive/lib.dr.iastate.edu/etd/16888/Tian_iastate_0097M_17740.pdf\|\|\|Fri Jan 14 21:07:21 UTC 2022
dc.subject.disciplines	Transportation
dc.subject.keywords	crash frequency
dc.subject.keywords	negative binomial regression
dc.subject.keywords	Safety performance functions
dc.subject.keywords	traffic safety
dc.subject.keywords	transferability
dc.subject.keywords	validation technique
dc.title	Examining the spatial and temporal transferability of safety performance functions: A case study for the Iowa interstate system
dc.type	article
dc.type.genre	thesis
dspace.entity.type	Publication
thesis.degree.discipline	Civil Engineering
thesis.degree.level	thesis
thesis.degree.name	Master of Science

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