Moth Effect: Determining Contributing Factors

The “moth effect” theory posits that drivers are attracted to or mesmerized by light much as moths are drawn to a flame. The notion that drivers are susceptible to the moth effect is born from the fact that vehicles stopped on the shoulder of a roadway are often struck by passing motorists, despite being obviously lighted and outside the lane of travel. There is very little practical highway transportation research on the moth effect, largely due to the difficulty of capturing the effect in a controlled setting. In fact, there is very little hard evidence that the effect exists at all. Even when a crash is speculated to be a result of the moth effect, that term is never used in an accident report. Therefore, circumstances surrounding crashes that could be a result of the moth effect are largely unknown. The goal of this research was to incorporate previous successful attempts at studying the moth effect. Research included tactics such as building fatigue, utilizing flashing versus steady lights, creating tasks with vehicles parked on the shoulder, and utilizing eye-tracking technology to determine gaze fixation and duration. The experiment carried out in this research effort was essentially a series of pilot studies where variables such as following distance, following duration, behavior of the lead vehicle, and the lead vehicle’s rear lights were varied from participant to participant with the goal of eliciting a moth effect and determining the variables that may have caused it. A moth effect behavior was defined as an instance when the participant driver left the lane of travel and steered toward a lead vehicle that had moved to the shoulder. There were a number of obstacles to overcome when researching the moth effect. For instance, despite the belief that driver over-fatigue and inebriation are major contributors to the effect, it was not feasible to permit over-fatigued or inebriated subjects to drive a vehicle as part of an experiment. To address fatigue’s contribution to the moth effect, this experiment immediately followed a separate experiment that involved participants driving for over an hour. Following the first experiment, those same participants were fitted with a calibrated eye tracker and asked to drive for another hour with the intent of causing more fatigue. The moth-effect experiment resulted in 1 of 21 participants exhibiting a moth-effect-like steering behavior. Factors contributing to this behavior included a close following distance to a lead vehicle (~100 feet), flashing hazard lights on the lead vehicle, and the participant not wearing an eye-tracking device. The participant exhibiting the moth-effect behavior, like other participants, experienced fatigue from the driving task, which involved driving for nearly an hour at 35 mph with the absence of radio, conversation, or any other tasks apart from following a lead vehicle. The authors believe that reduced alertness, akin to “highway hypnosis” (in which the driver operates the vehicle in a drowsy, trance-like state), may have also contributed to the driver’s behavior.