Description
Powered two-wheelers (PTWs) are a vulnerable class of road users with increased accident frequency and severity (Vlahogianni et al., 2012). In the early 1990s, motorcycle death-rate-per-mile-travelled was estimated to be 22 times the death rate for passenger cars (Preusser et al., 1995). In 2007, US motorcycle riders had a 34-fold higher risk of death in a crash than people driving other types of motor vehicles (NHTSA, 2007). In 2008, European motorcyclists represented 17 per cent of road fatalities while only accounting for 2 per cent of road users (IRTAD, 2009). In Greece this figure is as high as 33 per cent (IRTAD, 2013) while in Singapore it reaches 49 per cent with more than two motorcyclists being killed every week (Haque et al., 2012). Higher crash risk is associated to the fact that driver- and rider-related factors are much more prevalent in PTW accidents compared to vehicle- and environment-related factors. In particular, there exists a clear over-representation of inappropriate perception in PTW crashes (Van Elslande et al., 2013). One often discussed reason for perception failures is that PTW are less conspicuous than other motorized road users (Rößger et al., 2012). Consequently, gap acceptance is often inadequate due to the size-arrival illusion (Horswill et al., 2005); the latter refers to small objects being perceived to arrive later than larger ones. Besides conspicuity, car drivers seem to encounter difficulties in understanding PTWs’ manoeuvres and, thus, fail to foresee PTWs’ behaviour; foresight is the result of the combination of circumstantial data and permanent knowledge and beliefs (Ragot-Court et al., 2012).
Conspicuity can be examined from two different angles; namely the sensory and the cognitive perspectives. Sensory conspicuity is the visual distinction of an object due to its physical characteristics (Wulf et al., 1989). It refers to the extent to which an object can be distinguished from its environment because of its characteristics: angular size, eccentricity, brightness against the background, colour and so on. It reflects an object’s ability to attract visual attention and to be precisely located as a result of its physical properties (Rogé et al., 2012). The size and vehicle dynamics of PTWs are such that they have lower sensory conspicuity (Gershon and Shinar, 2013). Cognitive conspicuity depends on the distinction of an object based on the observer’s experiences and interests (Wulf et al., 1989). It is linked to the fact that an observer’s focus of attention is strongly influenced by his/her expectations, objectives and knowledge (Rogé et al., 2012). Interestingly, inappropriate expectations may be even more important in accident causation than the motorcyclist’s physical properties (Hole et al., 1996). PTWs show lower cognitive conspicuity as they account for relatively few vehicle miles travelled compared to automobiles, especially in Western countries (Gershon et al., 2012). Furthermore, not all car drivers have previous PTW riding experience. Helman et al. (2012) distinguishes further among:
- visibility: the extent to which an object stands out from its surroundings when observers are aware of its location;
- search conspicuity: the extent to which an object stands out from its surroundings when observers are searching for it within a scene;
- attention conspicuity: the extent to which an object stands out from its surroundings when observers are viewing the scene, but not searching deliberately for the object.
Vision is the predominant sensory modality used when driving (Crundall, 2011). Consequently, conspicuity is an important issue to all road users: be it cyclists (see, for example, Lacherez et al., 2013; Madsen et al., 2013); pedestrians (see for example, Tyrrell et al., 2004); or car drivers (see, for example, Alferdinck, 2004; Berg et al., 2007). However, evidence shows that vulnerable road users tend to underrate the role of visibility factors and conspicuity benefits (Lacherez et al., 2013) while overestimating their own conspicuity (Wood et al., 2013). Comparisons between bicycle and motorcycle crashes suggest that the majority of both crash types occur at intersections and are due to conspicuity issues (Haworth and Debnath, 2013). Nevertheless, PTWs seem to be more concerned due to a combination of factors including high speeds and acceleration rates (if compared to cyclists and pedestrians) and small size (if compared to other motorized road users).
Indeed, PTW conspicuity has been long been recognized as a critical PTW crash contributory factor. In 1975, the Greater London Road Safety Unit identifies a certain PTW over-representation in accidents. Detailed analysis of crash data followed. Results indicated that a major contributory factor was the failure of other drivers to observe PTWs in the general street scene (Lalani and Holden, 1978). Riders were then encouraged to wear bright clothing, preferably of fluorescent material and to switch on headlights during the daytime. A lot of research has been undertaken since 1975 on the so-called ‘PTW conspicuity hypothesis’. Accident investigations have been carried out in many countries and report that between half and three-quarters of motorcycle accidents involve collision with another vehicle (Huang and Preston, 2004). Markedly, most right-of-way (ROW) accidents involving PTWs are attributed to conspicuity (Pai et al., 2009) while drivers of other vehicles are at fault in the majority of two-unit motorcycle crashes (Haworth and Debnath, 2013).
In view of the above, this chapter’s objective is to examine the main determinants of riders’ accident risk which are related to conspicuity issues. We perform a literature review in order to explore the role of conspicuity in PTW crash occurrences. English-language publications were selected for relevance through a comprehensive search of major databases (see Table 1.1). The key words used in the search were: ‘conspicuity’ and ‘otorcycles’. To be included, papers were assessed against additional criteria; mainly relevance and publication date. The latter was thought to be critical as earlier literature reviews do exist. In the following section, we briefly discuss the effectiveness of conspicuity interventions. A detailed overview can be found in Chapters 41-0. In the third section, we review PTW accident risks and severity outcomes. Finally, we summarize findings and provide conclusions.