Cycling infrastructure (changes to the road environment) for reducing cycling injuries in cyclists

Review question

This review aimed to answer the question "what effect do different types of cycling infrastructure have on cycling injuries and collisions?". Cycling infrastructure involves changes which are made to the road design or management of the road for cyclists. We aimed to include studies which looked at the effects of three types of cycling infrastructure:

1. that which aims to manage the shared use of the road space for both motor vehicles and cyclists, for example, cycle lanes and shared use of a bus lane;

2. that which separates cycle traffic from motorised traffic and may include special routes just for cycle traffic, for example, cycle tracks and cycle paths. These may be shared with pedestrians;

3. management of the roads to include separation of motor vehicle and cycle traffic (for example, traffic rules that ban certain types of traffic from making particular turns) and cycle turns at traffic signals.

Comparisons were made with either routes or crossings that either did not have cycling infrastructure in place or had a different type of infrastructure. We were interested in studies with both adults and children. The primary outcome of interest was cycling injuries suffered as a result of a cycling collision. Secondary outcomes were collision rates for cyclists; and cycle counts, that is the number of cyclists using the infrastructure.

Background

Cycling infrastructure involves making changes to the road environment to provide special facilities for cyclists. These may include putting in cycle lanes or giving cyclists right of way at junctions, or separating cyclists from fast-moving or high-volume traffic. Speed limits may be introduced which means cyclists share the road with vehicles moving more slowly. This review is important because if we want to get more people cycling, we need to know whether cycling infrastructure helps to keep cyclists safe.

Search date

We searched world-wide research literature up to March 2015.

Study characteristics

The types of studies that could be included in this review are randomised controlled trials, cluster randomised controlled trials, controlled before-after studies, and interrupted times series studies. We found 21 studies looking at the effects of 11 different types of cycling infrastructure. No studies reported self-reported injuries or medically attended injuries. Fourteen studies reported police-reported ‘cycle crashes’ or ‘accidents’ or ‘injury crashes’ and the other studies reported outcomes such as number of “cycle accidents” or “crashes involving cyclists”. Nine studies reported collisions by severity; seven studies reported on age of casualty; and two studies reported on sex. One study reported on the level of social deprivation. Cycle flow was collected in 14 studies.

Key results

Generally we found a lack of evidence that the types of cycling infrastructure we looked at affects injuries or collisions in cyclists. Cycle routes and networks do not seem to reduce the risk of collision. Speed limits of 20 mph, changing parts of the road network to some designs of roundabouts and changing busy parts of a cycle route may reduce the risk of collision. In terms of severity of injury, sex, age and level of social deprivation of the area, there is a lack of evidence to draw any conclusions concerning the effect of cycling infrastructure on cycling collisions.

Quality of the evidence

We carried out a thorough search for relevant papers. The quality of the evidence was low with 20 of the included 21 studies using a controlled before-after study design. Few studies considered how factors such as weather and volume of traffic may affect collision rates. Few studies considered how changes in cycle rates seen as a result of installing infrastructure may affect changes in collision rates.

Authors' conclusions: 

Generally, there is a lack of high quality evidence to be able to draw firm conclusions as to the effect of cycling infrastructure on cycling collisions. There is a lack of rigorous evaluation of cycling infrastructure.

Read the full abstract...
Background: 

Cycling is an attractive form of transport. It is beneficial to the individual as a form of physical activity that may fit more readily into an individual’s daily routine, such as for cycling to work and to the shops, than other physical activities such as visiting a gym. Cycling is also beneficial to the wider community and the environment as a result of fewer motorised journeys. Cyclists are seen as vulnerable road users who are frequently in close proximity to larger and faster motorised vehicles. Cycling infrastructure aims to make cycling both more convenient and safer for cyclists. This review is needed to guide transport planning.

Objectives: 

To:

1. evaluate the effects of different types of cycling infrastructure on reducing cycling injuries in cyclists, by type of infrastructure;

2. evaluate the effects of cycling infrastructure on reducing the severity of cycling injuries in cyclists;

3. evaluate the effects of cycling infrastructure on reducing cycling injuries in cyclists with respect to age, sex and social group.

Search strategy: 

We ran the most recent search on 2nd March 2015. We searched the Cochrane Injuries Group Specialised Register, CENTRAL (The Cochrane Library), MEDLINE (OvidSP), Embase Classic + Embase(OvidSP), PubMed and 10 other databases. We searched websites, handsearched conference proceedings, screened reference lists of included studies and previously published reviews and contacted relevant organisations.

Selection criteria: 

We included randomised controlled trials, cluster randomised controlled trials, controlled before-after studies, and interrupted time series studies which evaluated the effect of cycling infrastructure (such as cycle lanes, tracks or paths, speed management, roundabout design) on cyclist injury or collision rates. Studies had to include a comparator, that is, either no infrastructure or a different type of infrastructure. We excluded studies that assessed collisions that occurred as a result of competitive cycling.

Data collection and analysis: 

Two review authors examined the titles and abstracts of papers obtained from searches to determine eligibility. Two review authors extracted data from the included trials and assessed the risk of bias. We carried out a meta-analysis using the random-effects model where at least three studies reported the same intervention and outcome. Where there were sufficient studies, as a secondary analysis we accounted for changes in cyclist exposure in the calculation of the rate ratios. We rated the quality of the evidence as ‘high’, ‘moderate’, ‘low’ or ‘very low’ according to the GRADE approach for the installation of cycle routes and networks.

Main results: 

We identified 21 studies for inclusion in the review: 20 controlled before-after (CBA) studies and one interrupted time series (ITS) study. These evaluated a range of infrastructure including cycle lanes, advanced stop lines, use of colour, cycle tracks, cycle paths, management of the road network, speed management, cycle routes and networks, roundabout design and packages of measures. No studies reported medically-attended or self-reported injuries. There was no evidence that cycle lanes reduce the rate of cycle collisions (rate ratio 1.21, 95% CI 0.70 to 2.08). Taking into account cycle flow, there was no difference in collisions for cyclists using cycle routes and networks compared with cyclists not using cycle routes and networks (RR 0.40, 95% CI 0.15 to 1.05). There was statistically significant heterogeneity between the studies (I² = 75%, Chi² = 8.00 df = 2, P = 0.02) for the analysis adjusted for cycle flow. We judged the quality of the evidence regarding cycle routes and networks as very low and we are very uncertain about the estimate. These analyses are based on findings from CBA studies.

From data presented narratively, the use of 20 mph speed restrictions in urban areas may be effective at reducing cyclist collisions. Redesigning specific parts of cycle routes that may be particularly busy or complex in terms of traffic movement may be beneficial to cyclists in terms of reducing the risk of collision. Generally, the conversion of intersections to roundabouts may increase the number of cycle collisions. In particular, the conversion of intersections to roundabouts with cycle lanes marked as part of the circulating carriageway increased cycle collisions. However, the conversion of intersections with and without signals to roundabouts with cycle paths may reduce the odds of collision. Both continuing a cycle lane across the mouth of a side road with a give way line onto the main road, and cycle tracks, may increase the risk of injury collisions in cyclists. However, these conclusions are uncertain, being based on a narrative review of findings from included studies. There is a lack of evidence that cycle paths or advanced stop lines either reduce or increase injury collisions in cyclists. There is also insufficient evidence to draw any robust conclusions concerning the effect of cycling infrastructure on cycling collisions in terms of severity of injury, sex, age, and level of social deprivation of the casualty.

In terms of quality of the evidence, there was little matching of intervention and control sites. In many studies, the comparability of the control area to the intervention site was unclear and few studies provided information on other cycling infrastructures that may be in place in the control and intervention areas. The majority of studies analysed data routinely collected by organisations external to the study team, thus reducing the risk of bias in terms of systematic differences in assessing outcomes between the control and intervention groups. Some authors did not take regression-to-mean effects into account when examining changes in collisions. Longer data collection periods pre- and post-installation would allow for regression-to-mean effects and also seasonal and time trends in traffic volume to be observed. Few studies adjusted cycle collision rates for exposure.

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