S. Hallmark, N. Hawkins, R. Thapa, S. Knickerbocker
In the US, some states have begun to address rural high-speed intersection crashes by physically restricting minor-road crossing movements to simplify driver decision-making in terms of gap acceptance. These treatments are referred to in Minnesota (USA) as reduced conflict intersections (RCIs). Introduction of RCI design has been successful in preventing severe crashes; however, the unusual design has been met with some apprehension from operators of agricultural equipment and large trucks. In particular concerns have been raised that, as large trucks are required to make U-turn maneuvers, they occupy the travel lanes for longer than would be required for a left-turn or through maneuver from the minor road, and, consequently, are exposed to on-coming high-speed vehicles for longer. In response to these concerns, this paper summarizes results of a study which collected and evaluated large vehicle operational behavior at three rural RCI intersections in Minnesota and three similar non-RCI intersections, which were proximate to the RCI intersections. Data were collected in 2015 using a portable video trailer array. Exposure time, evasive maneuvers, and other metrics were compared between RCI and regular intersections. Exposure time was calculated at both the intersections. Results show that large trucks are exposed 4 to 10 seconds longer while making a through or left turn maneuver at control intersections than they are making a U-turn. The average number of evasive maneuvers per large vehicle at either the merge or U-turn location were much lower than for the control intersection. This is significant since most agencies had concerns about the U-turn creating additional evasive maneuvers. Queue time and travel time were also compared. Gap acceptance behavior shows that minor stream vehicles are more likely responsible for evasive maneuvers of on-coming high-speed vehicles even for the larger accepted gap size at control intersections compared to merge and U-turn sections.
Keywords: alternative intersections; large vehicles; road safety; reduced conflict intersection