ATSSA: Improving Driver Behavior with Infrastructure Safety Countermeasures

14 Improving Driver Behavior with Infrastructure Safety Countermeasures CASE 8: Offset Right and Left Turns A nother roadway safety improvement that provides guidance to drivers is offset right- and left-turn lanes. To create an offset, the turn lane is moved laterally, so vehicles in opposing traffic lanes do not obstruct the view of the turning driver. A clear line of sight assists left-turning drivers by identifying an appropriate gap in oncoming traffic in which to turn, thereby reducing the potential for a collision between a turning vehicle and an oncoming vehicle. This safety improvement is appropriate for both unsignalized and signalized intersections. The benefit of reconfiguring 12 intersections in Wisconsin proved to be twice the construction cost of offsetting the left-turn lanes. A reduction in total, injury, left-turn and rear- end crashes was achieved at these locations through the use of this roadway safety improvement. An offset right-turn lane is an infrastructure treatment that assists drivers on the stop-controlled, minor-road approach to an expressway intersection. The right-turn lane on the expressway is offset laterally to provide the driver stopped on the minor road with a clear line of sight to oncoming vehicles on the expressway. By eliminating the view obstruction caused by the presence of right-turning vehicles in a conventional right-turn lane that is adjacent to the expressway through lanes, this infrastructure treatment assists drivers with identifying an appropriate gap through which to enter the nearside expressway intersection. This guidance also reduces the potential for a nearside right-angle collision between vehicles turning or crossing from the minor road and through vehicles on the divided highway. An evaluation of this treatment using a brief period of post-installation data at two locations in Iowa and one in Nebraska indicates that this can be an effective roadway safety treatment for reducing nearside right-angle collisions. One Iowa site achieved a 44 percent reduction in these types of crashes, while a Nebraska site had a total reduction of right-angle collisions. A reduction was not achieved at an Iowa site; however, this result could be attributable to a narrow median and alignment issue. ■ Figure 24. An offset turn (Image: Sean Coyle, Illinois Department of Transportation)