that curves are taken with practice, they are not described in any further detail for the sake of brevity. Discussion This study assessed the riding behaviour of novice, experienced and advanced riders navigating bends, both with and without hazards. It was predicted that advanced riders would adopt a more safety-conscious riding style, while novices might adopt a more risky racing line, sacrificing visibility for progression, and requiring more evasive manoeuvres on encountering a hazard. The results however paint a more subtle picture. In regard to the bends on which the hazards were located (L2B3), all riders adopted similar speeds, with a mean of 50 mph when the hazard first became visible. The first instinct of the riders was to decrease their speed before changing lateral position. Both the left and right bend hazards were initially visible in section 3 of the curve, leading to a significant decrease in speed by the time the riders reached the apex of the bend in section 4. This is clearly a response to the hazard, as no such reduction in speed was noted at the apex of any of the non-hazard bends. As lateral position only changed significantly by section 5, this suggests that it was a secondary response to the appearance of the hazard. However, analysis of lateral position also revealed group differences. For both the left and right bends, the advanced riders positioned themselves to optimise the balance of progression and visibility. While all riders moved from the outside of the curve towards the inside (indicative of a racing line), the advanced riders chose a shallower racing line which placed them closer to the outside of the curve when the hazard was encountered. This is comparable with the finding that police drivers tended to adopt a more central lane position than civilian drivers in a simulated driving task [26]. As a result, compared with the experienced riders, the advanced group had a significantly smaller shift in lateral position to avoid the left-hand bend hazard, and they did not need to make any significant shift in position to avoid the right- hand bend hazard. On the left hand bend, advanced riders did have to make a slight adjustment to their position to avoid the parked car, but riding any closer to the centre line would have been potentially dangerous if there had been any oncoming traffic. Therefore, advanced riders optimise visibility together with avoidance of collision with oncoming vehicles. Conversely it appears that on both the left and right hazard bends, the experienced riders adopted such early and pronounced racing lines that they required a considerable adjustment to their lateral position in order to avoid the hazards. For some individuals this may have been akin to swerving at the last moment to avoid the unexpected hazard. The hazard was visible at some point during section 3, even to those riders with the most pronounced racing lines. Therefore, while the early racing lines of the experienced riders will have reduced their visibility around the bend, these riders nevertheless managed to reduce their speed by section 4 along with the novices and advanced riders. However, although their initial responses in terms of speed are comparable with the other rider groups, the experienced riders had to reposition themselves more in order to avoid the hazard. One other outcome of the swerving manoeuvre is that it placed the experienced riders in a sub-optimal location in the exit spiral, where ideally they should have been preparing for the next bend. It appears that the experienced riders (and to a lesser extent, the novice riders) over-compensated slightly when avoiding the hazard, at least on the left-hand hazard bend. Conversely, the better positioning of the advanced riders through the apex of these bends allowed them to take up a more appropriate lane position in Motorcyclist Behaviour on Bends the exit spiral in preparation for the subsequent bend. Thus, advanced riders exhibited a safer strategy in the early part of the bend which produced better positioning for progression when exiting the bend. It is interesting to note however that, in regard to lateral position, the greatest distinction between safe and potentially unsafe riding styles was found in the comparison of the advanced and experienced rider groups rather than between the novice and advanced riders. The novice riders fell in-between the other two groups, behaving more like the experienced riders in the left hazard bend, but behaving more like the advanced riders in the right hazard bend. The novices’ behaviour on the right hand bend reflects their recent training: In preparation for the DSA test, novices are taught to move to the left of the lane to increase visibility through the bend. The novices’ behaviour on the left hand bend also reflects their recent training to a certain extent: Riders preparing for the DSA test are taught to maintain a more central lane position on left hand bends. Maintaining a central lane position leaves a greater margin for error in regard to avoiding potential collisions with oncoming traffic in the opposite lane, but means that further gains in visibility are sacrificed. This potentially explains why the novices do not move as close to the outside of the curve as the advanced riders, who still maintain a safe distance from any potential oncoming traffic but allow a smaller margin of error. At the apex of the bend, advanced riders are approximately 1 ft to the right of the centre of the lane. However, like the experienced riders, the novices move towards the left hand edge of the lane (approximately 2 ft to the left of the centre of the lane) as they approach the apex of the bend, which means that they have to make a severe adjustment to their lane position when they encounter the parked car. Since novice riders’ positioning was more akin to that of the advanced riders on right hand bends, this might help explain why fewer crashes occur on right hand bends compared to left ones [11–13]. While it could be argued that fewer right bend crashes are due to the greater visibility around right hand bends, or simply the fact that most riders are right-handed and may therefore find rightward steering easier to control, the systematic differences between the groups suggest that the majority of non-advanced riders will have a riskier approach in left hand bends than right hand bends. It is possible that riders base their behaviour on their individual mental models of road hazards. Experience is likely to lead to changes in the rider’s mental representation of the probabilities of different hazards occurring (cf. [27]). If a particular type of hazard is encountered frequently, it is more strongly represented in the rider’s mental model and it is intuitively perceived as being more likely to occur again. Conversely, if a hazard is encountered infrequently (or not at all), then the rider’s mental representation of this hazard diminishes. These mental representations of hazards are also likely to be affected by training, which primes riders to look out for certain types of hazard. Since DSA training of novice riders focuses on possible threats posed by oncoming traffic (i.e. maintaining left positioning on right hand bends and centre-lane positioning on right-hand bends), it is possible that novice riders have an increased representation of the probability of oncoming vehicle hazards in the opposite lane over other types of hazards when negotiating bends. In other words, novices might have been primed (perhaps even over-primed) to watch out for oncoming vehicle hazards, but might not have considered a stationary object in their own lane as a potential hazard. One could also argue that the behaviour of experienced riders represents their own intuitive understanding of the probabilities of such hazards occurring. While encountering an on-coming vehicle PLoS ONE | www.plosone.org 14 January 2012 | Volume 7 | Issue 1 | e29978