Setting Work Zone Speed Limits

Friday, March 3, 2017 - 16:15

Increasing travel demands and an aging highway infrastructure drive the need for extensive construction, maintenance, and utility work zones. The introduction of work zone environments creates risks for both drivers and construction workers due to changes from the normal driving environment. Temporary speed limit reductions are a common countermeasure aimed at improving work zone safety. In theory, reduced speed limits may serve at least three important functions: reduce variability in travel speeds and the potential for work zone crashes, reduce average travel speeds and the severity of crashes when they do occur, and enhance worker safety. Thus, understanding how reducing work zone speed limits impacts travel speeds is an important task.


This project evaluates the impacts of speed limit reductions on drivers’ speed selection at both aggregate and disaggregate levels. Data were collected from nine construction work zones in Iowa during 2014 and 2015. The lack of availability of data pertaining to the location, time, and type of activity significantly constrained the level of analysis that could be conducted for this research. Therefore, the crash analysis was not deemed reliable due to the inconsistency among the multiple data sets that were used to determine the location, time, and type of work zone activity. For the speed analysis, a quantile regression model was employed to examine the impacts of speed limit reductions on speed distribution quantiles before and during construction activities. The results show that speeds are consistently reduced when work zone speed limits are in place.  The full report is available from the Iowa State University web site at


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