Following car reduces motorcycles' size-arrival effect: A study using online experiments

Many fatal motorcycle accidents occur because car drivers infringe on motorcycle riders' right-of-way. The size-arrival effect refers to observers' tendency to judge larger objects as arriving sooner than smaller objects when estimating an approaching object's arrival time, which is one cause of right-of-way motorcycle accidents. Previous research has focused on a single vehicle that approaches the driver. However, it is also possible that a motorcycle approaches a driver along with other vehicles driving on multiple-lane roads. This paper presents the results of two online experiments; Experiment 1 validated the size-arrival effect when either a car or a motorcycle approached a driver waiting to turn across an intersection; and Experiment 2 investigated the size-arrival effect when a motorcycle and a parallelly driven car simultaneously approached the driver. Participants (n = 1723) in Experiment 1 and (n = 986) in Experiment 2 took part in the study. The results (1) validated the size-arrival effect; drivers accepted a smaller gap for approaching motorcycles than cars; (2) in the present settings drivers made turn decisions based on the distance gap rather than the time-to-arrival gap; (3) driver's acceptance of the gap when facing a motorcycle and a car was comparable to when facing only the car and significantly larger than facing only a motorcycle. These findings indicate that a car driving parallelly or behind a motorcycle reduces the size-arrival effect. These findings provide implications to suggest a safe riding strategy for motorcycle riders. We also suggest that such online experiments would facilitate studying large samples with less effort.