Dear Editor

My wife and I spent a couple of months cycling in the South Island last year. Apart from some cycling-friendly towns (eg Nelson, Wanaka) it was in general a terrifying and oppressive experience. Even on relatively quiet roads, overtaking traffic would often scrape past us in spite of our obvious visibility and bulk (because of our loads) and relative instability. Following traffic unable to overtake would loom along very close behind. And not infrequently we had the alarming experience of an oncoming overtaking driver coming straight at us leaving us nowhere to go. What a pity as we found the other aspects of NZ and its people to be warm and welcoming. There was a TV campaign when we were there named, I think, "imagine the bubble" whereby drivers are meant to imagine a cyclist to be surrounded by a bubble thus ensuring a safer overtake but few drivers seemed to have taken any notice. My point is that blame in crashes often is put on to the victim rather than the perpetrator, tables 3 and 4 indicate a reduction in accidents wearing high visibility clothing but there remains a very significant residue in the hi-vis group who did nevertheless have accidents. The solution must be either to have proper separation of cyclists and traffic or to ensure a much safer driving population maybe by strong legal sanction.

Dear Editor

As Thornley et al [1] indicate, the use of high-conspicuity aids by cyclists must be beneficial: motorists can only avoid collision with the cyclist if they can detect the cyclist.

Unfortunately, high-conspicuity aids are not likely to affect the visibility of the roadway environment around the cyclist, so motorists' perceptions of the cyclist's motion and distance will remain poor in conditions of night, fog and precipitation. Laboratory evidence shows unequivocally that perception of motion requires that the moving object be viewed against a visible background of other objects; without a visible background, the threshold for detecting the object's motion is extremely high [2].

One of the major cues for distance - motion parallax - is also dependent on a visible background. Motion parallax refers to movement of the retinal images of viewed objects as a result of the observer's movement; for example, viewing a distant point entails rates of retinal image motion inversely proportional to the distance of each of the objects from the observer. However, motion parallax is ineffective for perceiving an isolated object's distance [3]. Hence, the cyclist - for example, performing manoeuvres to left or right at a road junction - must be viewed against a visible roadway environment for motion parallax to be effective [4].

The argument presented here is underscored by the clear effectiveness of street-lighting in the reduction of pedestrian collisions with motor vehicles [5] - the pedestrian AND the roadway environment are made more conspicuous. This outcome must extend to cyclists.

The conclusion must be that the value of high-conspicuity aids should not be overstated: fundamental aspects of the motorist's perception must remain weak.

References

1. Thornley SJ, Woodward A, Langley JD, Ameratunga SN, Rodgers A. Conspicuity and bicycle crashes: preliminary findings of the Taupo Bicycle Study. Inj Prev 2008;14:11-18.

2. Reinhardt-Rutland AH. Induced movement in the visual modality: an overview. Psychol Bull 1988;103:57-72.

3. Reinhardt-Rutland AH. Motion parallax. In Craighead WE, Nemeroff CB (eds.). Encyclopedia of psychology and behavioral science (pp 977-979). New York: Wiley.

4. Reinhardt-Rutland AH. Some implications of motion-perception evidence and theory for road accidents. J Int Assoc of Traffic and Safety Sci 1992;16:9-14

5. Retting RA, Ferguson SA, McCartt AT. A review of evidence-based traffic engineering measures designed to reduce pedestrian-motor vehicle crashes. Am J Public Health 2003; 93: 1456-1463