Stephen Rees's blog

Thoughts about the relationships between transport and the urban area it serves

Posts Tagged ‘traffic circles

Traffic circles bad: cycle tracks good

with 13 comments

The research has a much less digestible title

“Comparing the effects of infrastructure on bicycling injury at intersections and non-intersections using a case–crossover design”

But it is worth reading the whole thing which is available on line

Abstract
Background

This study examined the impact of transportation infrastructure at intersection and non-intersection locations on bicycling injury risk.

Methods

In Vancouver and Toronto, we studied adult cyclists who were injured and treated at a hospital emergency department. A case–crossover design compared the infrastructure of injury and control sites within each injured bicyclist’s route. Intersection injury sites (N=210) were compared to randomly selected intersection control sites (N=272). Non-intersection injury sites (N=478) were compared to randomly selected non-intersection control sites (N=801).

Results

At intersections, the types of routes meeting and the intersection design influenced safety. Intersections of two local streets (no demarcated traffic lanes) had approximately one-fifth the risk (adjusted OR 0.19, 95% CI 0.05 to 0.66) of intersections of two major streets (more than two traffic lanes). Motor vehicle speeds less than 30 km/h also reduced risk (adjusted OR 0.52, 95% CI 0.29 to 0.92). Traffic circles (small roundabouts) on local streets increased the risk of these otherwise safe intersections (adjusted OR 7.98, 95% CI 1.79 to 35.6). At non-intersection locations, very low risks were found for cycle tracks (bike lanes physically separated from motor vehicle traffic; adjusted OR 0.05, 95% CI 0.01 to 0.59) and local streets with diverters that reduce motor vehicle traffic (adjusted OR 0.04, 95% CI 0.003 to 0.60). Downhill grades increased risks at both intersections and non-intersections.

Conclusions

These results provide guidance for transportation planners and engineers: at local street intersections, traditional stops are safer than traffic circles, and at non-intersections, cycle tracks alongside major streets and traffic diversion from local streets are safer than no bicycle infrastructure.

This confirms what I have been saying on this blog for a long time. The type of traffic circle that is so extensively used in Vancouver (and that is where this research was done) is not an improvement. The evidence shows that they actually increase risk. Casual observation will quickly confirm that while some drivers slow down, many regard them as a challenge.

The illustration and caption below comes from the report. Anthony Floyd pointed out on Twitter that this one “(7th/Highbury) is one of the better ones: lots of visibility, rarely a problem there.  The ones a few blocks before, from Balsam right up to Collingwood, are utterly useless and dangerous, however.”

A typical traffic circle found in residential areas of Vancouver, designed to calm motor vehicle traffic, but found to increase risk at intersections of local streets in this study. (A) Photograph as viewed from the perspective of an approaching cyclist. (B) Design dimensions of traffic circle (derived from measurements taken throughout the city). The dashed arrow shows the route a cyclist is required to take when turning left.

I have also seen drivers make left turns simply by going round the circle the wrong way. In a number of locations (such 29th Avenue at Blenheim) the City has added signs saying “Yield to traffic in circle” which has absolutely no discernible effect on drivers on Blenheim – which they regard as the arterial – to the peril of any road user on 29th which also happens to be a bike route.

Time for the City to revise its approach, and if there is no room for a correctly designed roundabout, revert to the four way stop – which at least the locals seem to both understand and usually comply.

The other one is that separated bike lanes reduce collisions for cyclists – no surprise there.

Written by Stephen Rees

February 17, 2013 at 5:10 pm