Materiales pétreos naturales: Cantería y mampostería

Despite randomised controlled trial evidence that conspicuity aids can increase the detection and recognition distances for observers of cyclists and pedestrians in road environments, the effect of their use on the risk of traffic collisions involving pedestrians or cyclists has not been tested with a rigorous randomised intervention trial 9 (updated 2009).

There is some observational study evidence regarding the use and efficacy of conspicuity aids by cyclists. In a recent study from New Zealand researchers examined the relationship between self-reported injury crash and fluorescent clothing use by collecting data from volunteers using a web-based questionnaire in a cohort of cyclists registered for a 100 kilometre leisure ride around lake Taupo83_{. The study found that 29.8% of respondents reported always wearing} fluorescent colours when riding. The adjusted incident rate ratio for all crashes if respondents recorded that they “always wear fluorescent colours” was 0.73 (95%

CI 0.57 to 0.93). The incidence rate ratios for all crashes for “always use a front

light [or back light] after dark” “yes” vs. “no” were 0.83 (95% CI 0.55 to 1.27)

and 1.59 (95% CI 1.09 to 2.31) respectively. The results suggest that the

adjusted incident rate ratio of having a crash resulting in any days off work (interpreted as a more severe incident than “all crashes”) was 8.33 (95% CI 2.6 to 26.7) for never wearing fluorescent clothing vs. always wearing them. Lower, but still significant rate ratios, were found for crashes resulting in inability to complete daily activities for >24 hours using the same exposure comparisons. Retro-reflective materials were not found to be linked to reduced crash involvement in this study. Whether crashes involved other road users or were the result of a loss of control was not reported. It is therefore impossible to assess to what extent the findings are actually attributable to the protective effect of fluorescent colours or other conspicuity measures and not merely evidence of confounding from other crash predictors such as cautious riding style by those choosing fluorescent garments to increase their conspicuity.

There is a considerable risk of bias in the study owing to attrition at various stages of the recruitment and data collection process. The survey was web- based and therefore excluded those without email addresses (>50%). Of those approached 1612 (29%) refused to take part and a further 1519 (27%) failed to complete the study instrument having started it possibly owing to its length and complexity.

The authors acknowledge the possibility of residual confounding from risky behaviour and reduced propensity to use conspicuous attire. The study did attempt to control for confounding from this source by calculating a measure of average speed of travel. They found that higher average speeds were associated with reduction in injuries (incidence rate ratio 0.20; 95% CI 0.06 to 0.67) but not crashes (incidence rate ratio 0.81 (064 to 1.04) but lower speeds were associated with greater numbers of crashes and injuries (incidence rate ratios

2.09; 95% CI 1.71 to 2.55) and 3.52; 95% CI 1.30 to 9.48) respectively).

Greater speed may be associated with greater skill although there was no apparent dose response from greater levels of experience.

Further evidence for a protective effect of conspicuity aids for vulnerable road users has been reported. A large population level case-control study of motorcyclists was undertaken in New Zealand which attempted to measure the direct effect of conspicuity aid use on crash risk 213. The study was able to demonstrate a protective effect; multivariate-adjusted odds ratio of motorcycle injury crash when wearing any item of reflective or fluorescent clothing was 0.63 (95% CI 0.42 to 0.94). The authors go on to estimate a population attributable risk of 33% for motorcycle injury from not using conspicuity aids assuming complete adoption of the exposure and no confounding of the main outcome. The authors managed to follow-up a large proportion of the motorcyclists involved in crashes, recruited suitable community controls and considered a range of confounders thought to be important. This study provided a model for how such research could be conducted in cyclists.

It was not reported in the original paper whether motorcycle drivers had been involved in collisions or single-vehicle crashes i.e. where there could be no plausible protective role for conspicuity aids. The authors did subsequently report that they had recorded collision crash involvement but had included all configurations in the analysis they published 214. They report that “over 70%” of crashes were multi–vehicle and that subgroup analyses showed “very similar” findings. However the inclusion of these cases is difficult to justify given that relative conspicuity is irrelevant to these types of crashes. It is likely that this apparent effect is evidence of uncontrolled confounding from lower levels of risk- taking behaviour by conspicuity aid users.

No randomised studies were indentified which attempted to demonstrate any association between conspicuity aids use and crash risk for cyclists or pedestrians. Kwan and Mapstone caution that the measurable benefits of conspicuity aid use, though unambiguous, may not translate into reductions in crashes and injuries in real traffic situations. Many other factors could reduce the protective effect below its theoretical potential such as how, when and where such aids are used. Further influential factors, such as the interrelation of conspicuity aid performance and the degree of “field dependence” i.e. the variable ability of an observer to extract relevant information about an object against a given background, have not been adequately investigated in the case

of motorcycles 215 and may be of relevance to cyclists. Some interactions between conspicuity aid performance and factors such as observer age have been studied 205 216. These studies suggest that the protective effect of conspicuity aids may depend to an unknown extent, on various characteristics of the driving population and environmental conditions such a scene complexity in which cyclists and motor-vehicles interact.