bends and braking and acceleration effects [23]. Speed and lateral position of the rider were recorded at a frequency of 10Hz. The scenario was presented on a large flat-screen (285cm6228cm with a resolution of 128061024) at a distance of 190cm in front of the rider. A speedometer, tachometer, gear selection and view of the road behind the rider were presented at the bottom of the screen. Auditory feedback of engine noise (based on current rpm) was also provided using surround sound speakers. A bespoke scenario was developed for the study which covered a total distance of 101,000 ft (30,793m). The scenario comprised two laps of a simulated route which included a mixture of urban, suburban and rural roads, with riders spending approximately an equal amount of time in 40 mph speed limit zones (i.e. urban and suburban) and 60 mph zones (i.e. rural). Within the scenario, a number of sub-scenarios were designed to investigate different aspects of riding behaviour [25]. Of interest in the current paper are the left-hand and right-hand S-bends, embedded in one of the rural sections of the riding scenario. The S-bends comprised eight pairs of opposing left- and right- hand bends designed to mimic riding a series of bends in a rural setting with a speed limit of 60 mph. There was a set of 4 left-hand bends, each immediately followed by an opposing right-hand bend. This was followed by a 7400 ft section of straight road, then a set of 4 right-hand bends, each immediately followed by an opposing left- hand bend. Left-hand bend data were collected from the first set of bends, and right-hand bend data were collected from the second set (i.e. the relative opposing bends in each set of bends were not analysed). Data from the first bend in each set were excluded from any analyses, so that only bends 2, 3 and 4 were analysed. This ensured that the road geometry was identical immediately before each analysed bend, since approach position was likely to be affected by the preceding manoeuvre. Maps of the left-hand S- bends and the right-hand S-bends are shown in Figure 1. Motorcyclist Behaviour on Bends The bends were 700 ft long and comprised a 500 ft section with constant curvature of 0.0025 (equivalent to the reciprocal of the radius in feet) preceded by a 100 ft entry spiral (in which the curvature of the road increased linearly from 0 to 0.0025) and followed by a 100 ft exit spiral (in which the curvature of the road decreased linearly from 0.0025 to 0). Both sets of S-bends were preceded by a standard UK warning sign for bends ahead, positioned 600 ft before the first bend. Trees were positioned either side of the road from 1100 ft before the bends to approximately 3000 ft after the bends. In addition, an embankment on either side of the road was designed to prevent the rider from ‘seeing through’ the bends. However it was possible to ascertain the road layout from the tree-line beyond the vanishing point of the road. On the second lap, a hazard appeared on bend 3 (L2B3) in both the sequence of left-hand bends and the sequence of right-hand bends. On the left L2B3 a stationary car was positioned 150 ft beyond the apex of the bend (Figure 2: left panel). If the rider was positioned close to the centre line as they progressed around the left-hand bend, the car was visible at a distance of 289 ft. However, if the rider was positioned nearer to the kerb, the car only became visible from 263 ft away. For the right-bend hazard a car travelling in the opposite direction was positioned legally but close to the centre line of the road. When the motorcyclist reached a point 150 ft prior to the apex of the bend, the car was initially positioned 150 ft beyond the apex of the bend, and travelled at a constant speed of 6.8 mph (Figure 2: right panel). A slow speed was chosen so that the vehicle was encountered by each participant approximately at the same point on the road. If the rider was positioned to the left hand side of the road upon entering the bend, the car became visible when the rider was approximately 300 ft from the hazard. No other vehicles appeared in this part of the route, Figure 1. Schematic depictions of the road geometry of left-hand S-bends (left panel) and right-hand S-bends (right panel). The dark grey boxes represent analysed bends (i.e. bends 2, 3 and 4). The dots in Bend 3 denote the positions of the hazards. Entry point into the S-bends and direction of travel are represented by arrows. doi:10.1371/journal.pone.0029978.g001 PLoS ONE | www.plosone.org 4 January 2012 | Volume 7 | Issue 1 | e29978