Motorcycle Accident Risk Could Be Inflated By a Time to Arrival Illusion

The most common motorcycle/car accident involves a car violating a motorcyclist's right of way. One possible explanation for this is the size-arrival effect in which smaller objects are perceived to arrive later than larger objects. That is, drivers may estimate the time to arrival of motorcycles to be later than cars because motorcycles are smaller. This article reports on a study of arrival time judgments that used a temporal occlusion paradigm. Drivers recruited from the student population saw video footage of oncoming vehicles and had to press a response button when they judged that vehicles would reach them. In the first experiment (n = 28 students), the time to arrival of motorcycles was estimated to be significantly later than larger vehicles (a car and a van) for different approach speeds and viewing times. In the second experiment (n = 33) the authors investigated an alternative explanation to the size-arrival effect: that the smaller size of motorcycles places them below the threshold needed for observers to make an accurate time to arrival judgment using tau (optical size divided by the rate of optical expansion). The authors found that the motorcycle/car difference in arrival time estimates was maintained for very short occlusion durations when tau could be estimated for both motorcycles and cars. The authors conclude that their results are consistent with the size-arrival effect and are inconsistent with the tau threshold explanation. The authors propose that drivers should be educated about the illusion that may exist when judging whether to pull into the path of an oncoming vehicle; this illusion may lead them to choose smaller gaps in front of smaller vehicles such as motorcycles.

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  • Authors:
    • Horswill, Mark S
    • Helman, Shaun
    • Ardiles, Pablo
    • Wann, John P
  • Publication Date: 2005-8


  • English

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  • Accession Number: 01010606
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Nov 26 2005 7:25AM