Impulsividad

The main limitation of this research was sample size. The small sample size of 110 safety critical events created some hurdles in building statistical inferences from the logistic regression model. Some of the variables in work zone related-data were combined for the purpose of analysis due to small sample size and diversity of categories in each variable. Small sample size is a main issue in analyzing some of the predominant factors in our data set. For example, all type of cell phone-related distractions were combined (e.g. talking, texting, browsing, dialing, holding, locating, reaching, and other). Also, the effect of texting and cell phone usage on the outcome of an event could not be verified due to the small sample size.

Baseline events were not matching comparable work zone configurations, as the baseline events were coded for only 21 seconds duration. The segment of work zones coded

could occur in any area of the work zone (upstream, work area, or downstream). Therefore, none of the baseline events include full driving trace from the upstream all the way

throughout the work area and termination of the work zone.

The baseline data is limited to 89 observations including multi-lane highways only due to time and budget constraints. This may not be representative of all the SHARP 2 NDS baseline data and may affect our results.

All in all, sample size was the major limitation of this study. Due to the scarce number of the safety critical events in the NDS data, it is recommended to use crash surrogates to model the safety impacts associated with work zones. As this research found speed as the major contributing factor to the safety critical events, it can be used as a crash surrogate. The NDS data revealed speed data as the most complete collected variable to be used as a crash surrogate.

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CHAPTER 3. MULTIPLE CHANGEPOINTS DETECTION OF SPEED