Intervenciones realizadas con anterioridad

The road environment in which cyclists travel and in particular elements such as traffic speed, volume and composition, may have significant effects on the likelihood of being involved in a collision crash. Given these factors the availability and quality of dedicated cycle infrastructure may influence bicycle crash risk.

The vast majority (82%) of UK cycling accidents occur in an urban setting 94 although the proportion of fatalities occurring there is lower (65%) than for rural roads 88. Richter reports a figure of 95.7% of cycling accidents occurring in urban areas in Germany 95 but variations are likely to occur between different

speed roads and levels of enforcement and adherence to speed restrictions making direct comparisons between countries difficult.

Jones analysed variations in road mortality and morbidity across different counties in England and Wales using data from 1995 to 2000 96. After adjustment for a large number of confounding factors there remained significant differences in injury rates between different counties. The burden of road injury at county level was significantly positively associated with total length of road system, relative deprivation, per capita car ownership and average daily traffic levels. A higher proportion of roads classed as “minor” and greater total curvature of roads were associated with lower casualty rates. Nottinghamshire was located in the top ten of counties with higher than expected road casualty rates in the adjusted models. Cycling was not disaggregated in this analysis owing to the relatively small numbers of incidents involved.

Other work has examined variations in the numbers of traffic injuries by mode and by comparing urban vs rural locations 97. This analysis suggests that cycling injury rates are likely to vary to a greater extent because of greater differences in exposure between different local authority areas and that therefore injury rates per head of population were misleading. Cyclist casualty rates have also been shown to vary with land use with retail areas giving rise to more accidents in working hours 98 than residential areas.

Roundabouts have been shown to present raised risks of crashes for cyclists. Daniels compared before and after bicycle crash rates for junctions replaced by roundabouts by comparison to nearby unchanged junctions to account for secular trends in safety and regression to the mean from the effect of high crash rates leading to junction reconfigurations 334. The odds ratio for an injury crash at roundabouts compared to other junction types were 1.27 and 1.48 for roundabout in non-urban and urban settings respectively. A study in Denmark found a marked association between traffic volume and speed, and risk of cyclists crashes at roundabouts in Odense 99.

A Canadian study of commuter cyclists which reported collision rates per unit of distance, found that there were 3.26 collisions per million kms travelled in the Ottawa-Carlton area with collisions more likely on the road than on segregated cycle facilities but much more likely when cycling on sidewalks 144. The same authors found a much higher rate for commuter cyclists in central Toronto (82 per million kms) a much more urbanised and motorised area but similar differences depending on infrastructure type used.

A study in the US calculated a “relative danger index” for different road types and cycle lanes by calculating the proportion of reported crashes per distance travelled 333. Cyclists using major or minor roads with or without cycle lanes were at lower risk of crashes than those using mixed use “trails”, cycling off- road or on “sidewalks” ( “major” street without bike facilities = 0.66; “minor” street without bike facilities= 0.94; on-road bike routes = 0.51; on-road bike lanes =0.41 vs. “multi-use trails” = 1.39; off-road routes =4.49; “other (mostly sidewalks)” = 16.3. However these studies were of self-reported crashes and locations and the purposes for which journeys were undertaken are likely to have been very different across the location types.

Street lighting is widely assumed to reduce crash risk. A systematic review of randomised controlled trials, non-randomised controlled trials and controlled before-after studies compared the effects of new installations or improvements in street lighting on all road traffic crashes 196. The pooled relative risk of the effect of street lighting compared to day-time control periods showed a reductions in risk of all road crashes (RR 0.68; 95% CI 0.57 to 0.82), injury crashes (RR 0.68; 95% CI 0.61 to 0.77 and fatal crashes (RR 0.34; 95% CI 0.17 to 0.68) although the methodological quality was rated as “generally poor”. In a study of adult cyclists injured in collisions with cars in the Czech Republic between 1995 and 2007 192 a multivariate regression analysis compared the ratio of fatal to all severities of cycle crash under different conditions compared to daylight. There was no significant difference in odds of fatal vs. non-fatal crashes on streets with lighting after dark although areas with no street lighting were found to be significantly more likely to result in fatal injuries (odds of fatal crash under street lighting vs daylight 1.07; 95% CI 0.83 to 1.37 and no street lighting in darkness vs daylight 2.16; 95% CI 1.75 to 2.67).

In the US data for 1991 showed that the deaths of cyclists in collisions with motor vehicles occurring after dark were equally prevalent in street lighted vs. unlit areas 197. In a large study of Dutch collision records the effect of street lighting in improving safety of road users was highest for cyclists and pedestrians 198. Crash risk for all cyclists was increased after dark but on lit roads this increase was 81% (95% CI 61-105%) whereas for unlit roads it was 429% (95% CI 303-596%). The same study demonstrated a reduction in this beneficial effect during rain (-44%), fog (-26%) and snow (-26%).

The quality of road surface may affect the risk of bicycle crashes but is unlikely to have a significant impact on collision crashes although this has not been

studies directly. An American study failed to find a significant association between injury severity of cyclists and riding on paved vs. unpaved surfaces 147. The odds ratio for bicycle crash within the previous year was found to be lower for bike paths and far higher for off-road trails by comparison to roadways in anther US study (OR 0.6 and 7.17 respectively) 136.

There is currently no evidence regarding the contribution of actual measured traffic speeds and composition to bicycle crash risk. The available evidence from studies of infrastructure and land use cumulatively suggest that environmental factors such as road type have an important influence on the numbers of injuries that occur and that these variations may be more pronounced for cycling crashes than for other modes of travel.

Recently a more detailed study of the geographical variation in crash risks for cyclists has been proposed 100. This study seeks to examine and compare the environmental characteristics of cycle crash and non-crash sites using a case- crossover design. A blinded comparison of each cyclist’s crash site with two other randomly selected controls sites along the route to assess the possible influence of infrastructure, cyclist traffic volume and motor vehicle volumes and speeds. This marks a move away from a sole focus on cyclist characteristics towards a greater understanding of the effects of environmental factors such as infrastructure and traffic volumes on crash risk for cyclists.