Estimation of Relationships Between 85th-Percentile Speed, Standard Deviation of Speed, Roadway and Roadside Geometry, and Traffic Control in Freeway Work Zones

Understanding speed behavior in construction work zones is critical to making appropriate geometric design, roadside design and traffic control decisions. Gaps exist in national work zone design guidance. Since speed related measures play a central role in design and traffic control decisions, the lack of comprehensive and consistent guidance has contributed to several observed and undesirable speed-related outcomes. The objective of this research is to investigate predictive relationships between free-flow speed behavior, roadway geometrics, and traffic control in construction work zones on freeways. Speed behavior was studied through the testing of two empirical model structures, ordinary least squares and seemingly unrelated regression, which relate the dependent variables, 85th percentile free-flow speed and standard deviation of free-flow speed to predictor variables (work zone geometry and traffic control). Parameter estimates, standard errors and formal statistical testing indicated that ordinary least squares regression was appropriate for the data. Several variables related to work zone configuration, infrastructure type, geometric design and traffic control were found to be statistically significant predictors of 85th percentile free-flow speed and standard deviation of free-flow speed.