Drivers adapt - Be prepared for It!

Behavioral adaptation refers to the change in road user behavior in response to new conditions (Kulmala & Rämä, 2013). Behavioral adaptation can improve safety, but it can also reduce or even eliminate anticipated safety benefits of many well-intentioned road safety countermeasures. To expect driver behavior to remain the same after the implementation of a change in the road, vehicle, or driving environment, is naïve. Empirical studies that do not consider the full range of behavior affected by a countermeasure may similarly overlook the consequences of behavioral adaptation. This paper considers a number of examples of driver safety countermeasure implementation where unexpected results occurred and behavioral adaptation was the likely culprit. These examples are drawn from highway design, traffic control device design, vehicle countermeasures, enforcement countermeasures, driver education countermeasures and impaired driving policies. A previously presented inventory of characteristics to consider when estimating the likelihood for behavioral adaptation (Rudin-Brown et al., 2013) is expanded and presented within the context of the Qualitative Model of Behavioral Adaptation (Rudin-Brown & Noy, 2002; Rudin-Brown, 2010), in the hopes of addressing the question "When can we anticipate the safety effect of a treatment, and when not?"