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Powered two-wheelers (PTWs) such as motorcycles, mopeds, and scooters are becoming increasingly popular worldwide. However, this rise in popularity has also come with safety concerns. While deaths among car passengers have steadily declined in recent decades, fatalities involving mopeds and scooters have shown the opposite trend (Penumaka et al., 2014). In fact, statistics show that riders of these vehicles are 20 to 40 times more likely to be killed in a crash than car occupants for the same distance traveled (Blackman & Haworth, 2013).

Many PTW crashes occur when another driver—often in a car—fails to give the rider the right-of-way and crosses their path (Chen et al., 2018; Pai, 2011). One explanation for this is that drivers may have trouble accurately judging how fast a scooter or motorcycle is approaching. Because these vehicles are smaller, drivers may miscalculate the time-to-collision (TTC), or how soon the two vehicles will meet (Pai, 2011).

Many visual cues influence how people judge TTC. One example is the “size effect”: people tend to think that larger objects will arrive sooner than smaller ones, even when the smaller object is actually closer (DeLucia, 2013). In driving contexts, this bias means that cars and trucks are typically judged as approaching faster than motorcycles, even when their actual TTC is the same (Horswill et al., 2005). Practically, this leads drivers to be more cautious around larger vehicles while underestimating the risk posed by smaller PTWs. As a result, riders of PTWs may face higher crash risks because other road users misjudge how quickly they are approaching.

References

Blackman R, Haworth N. 2013. Comparison of Moped, Scooter and Motorcycle Crash Risk And Crash Severity. Accident Analysis & Prevention. 57:1-9.

Chen PL, Chen YC, Pai CW. 2018. Motorcyclist Is the Right-of-Way Violator: A Population-Based Study of Motorcycle Right-of-Way Crash in Taiwan. Journal of Advanced Transportation. 2018:7.

DeLucia PR. 2013. Effects of Size on Collision Perception and Implications for Perceptual Theory and Transportation Safety. Current Directions in Psychological Science. 22(3):199-204.

Horswill MS, Helman S, Ardiles P, Wann JP. 2005. Motorcycle Accident Risk could be Inflated by a Time to Arrival Illusion. Optometry and Vision Science. 82(8):740-746.

Pai CW. 2011. Motorcycle Right-of-Way Accidents - A Literature Review. Accident Analysis & Prevention. 43(3):971-982.

Penumaka AP, Savino G, Baldanzini N, Pierini M. 2014. In-depth investigations of PTW-car accidents caused by human errors. Safety Science. 68:212-221.