Behavior Study of Merge Practices for Drivers at Work Zone Closures
Lane-straddling vehicle blocks two vehicles upstream
Start date: 11/15/09
End date: 11/30/10
Report: Behavior Study of Merge Practices for Drivers at Work Zone Closures (2.99 mb pdf) June 2011
- Iowa Department of Transportation
- Midwest Transportation Consortium
- Smart Work Zone Deployment Initiative
About the research
The purpose of this project was to determine which driver behaviors result in the greatest reduction of capacity with work zone lane closures. Traffic and safety experts believe that driver behaviors, such as forcing late mergers, tailgating, queue jumping in the closed lane or on the shoulder, and other aggressive behaviors have the greatest impact on maximum flow rates. Other behaviors that create excessive headways or slow speeds can also reduce maximum flow in the taper. The objectives of this project were to identify and document driver behaviors that are the most detrimental to work zone traffic flow and safety.
Data were collected at freeway work zones for six days to identify behaviors that affected work zone safety and operations, which included forced and late merges, lane straddling, and queue jumping. Queue jumping occurs when a driver already in the open lane decides to jockey for a better position by moving to the closing lane and passes one or more vehicles before merging back to the open lane.
A total of 30 vehicles queue jumped during the study period. However, vehicles only improved their position in most cases by one vehicle. The queue jumping also resulted in four forced merges, eight late merges, and four late forced merges, indicating that queue jumping has an impact on operations. In addition, queue jumping appeared to evoke aggressive behavior by other drivers, which was manifested by lane straddling and, in some cases, vehicles physically trying to block queue jumpers.
Lane straddling occurs when drivers move to straddle the lane line separating the open and closing lanes with their vehicles. Drivers who lane straddle attempt to prevent vehicles behind them from late merging or moving ahead of them in the queue.
The lane straddling incidents observed in this study often involved several vehicles. Of the 51 incidents that were noted, lane straddling resulted in one forced merge, two late merges, and 14 forced late merges. The main operation impact is that lane straddling creates forced merges that may not have otherwise occurred. In addition, in several cases, drivers who engaged in lane straddling in this study ended up slowing down the entire queue behind them, as they attempted to prevent a driver behind them from using the space they left when they moved over to lane straddle.
This study identified behaviors that compromise safety in work zones. Forced merges, which are discussed as operational problems, are also safety problems, because a driver behind a forced merge has to slow or, in some cases, take some evasive action to avoid colliding with the merging vehicle. Queue jumping also compromises safety, because it creates forced merges and often resulted, in this study, in aggressive actions by other drivers.
Lane straddling can also compromise safety by creating forced merges that may not have otherwise occurred. Lane straddling also resulted in several other safety-compromising behaviors: drivers using the shoulder to pass lane-straddling vehicles, drivers attempting to merge into the space previously occupied by the lane-straddling vehicle and resulting in the lane-straddling driver attempting to physically block the merging vehicle, and, in one case, drivers racing abreast until reaching the arrow board, where a forced merge occurred.