Stephen Rees's blog

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

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

13 Responses

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  1. * The first thing to do, is switch from “traffic circle” to “roundabout” whre people have to slow down to yeld traffic before entering the intersection (at the difference of the traffic circle).

    Mini roundabout are definitely much safer than any other method, especially 4 way stop). and result doesn’t suffer discusion: 77.1% reduction of injury in the case of Toulouse, France)
    (http://www.certu.fr/IMG/pdf/valuation_des_mini-giratoires_a_Toulouse.pdf and that also apply for cyclist.

    So what happen in Vancouver?

    certainly bad design – the linked pdf gives example of good design

    But also a acute reckless behavior from helmeted cyclists in Vancouver :
    A careful reading of the bmj study shows that half of the cyclist injured on traffic circle interesection, are self injured (not involving third party) – basically because going way too fast in the interesection and unable to control their bike in the circle (at the 4 ways stop, they get hurt only when another vehcile do the same, so odd of accident is reduced, thanks to the fact there is not that much cyclists in Vancouver).

    So remove the reckless cyclist, and the conclusion of the study become different. The problem is the one of reckless behavior by helmetted cyclist.

    Voony

    February 17, 2013 at 8:20 pm

  2. Are the statistics still relevant in Europe? Perhaps Canada needs some education on how to use a roundabout.

    Susan Chapelle

    February 17, 2013 at 8:30 pm

  3. Cars parked too close to roundabouts reduce sightlines and decrease turning radii. There aren’t any parked cars near any of the roundabouts in the Toulouse presentation.

    mike0123

    February 17, 2013 at 9:44 pm

  4. [...] So, despite the City’s efforts at making intersections safer, I’ve long held the opinion that traffic-circles are in fact more dangerous for cyclists. Recent studies on Vancouver’s cycling infrastructure have shown that very thing. A UBC study that I’ve linked to in the past suggests that, and a recent study comes to the same conclusion. (Hat-tip to Stephen Rees who also has a poor opinion of Vancouver’s traffic circles). [...]

  5. I never thought the point of traffic circles was to reduce the risk to cyclists, at least not directly. I though the point was to give cyclists a quick route with minimal traffic. The traffic circle ensures cyclists don’t need to stop every 100 meters but cars are sufficiently slowed down as to not create shortcut routes. Presumably an Idaho Stop law would accomplish the same thing, but good luck convincing the government to implement that. Personally, I’d be much more likely to bike on Main instead of Ontario or Broadway, instead of 10th if every intersection had 4-way stops instead of traffic circles.

    canadianveggie

    February 18, 2013 at 11:45 am

  6. Are traffic circles common on bikeways? I would have thought that the bikeway would get priority (with 2-way stops from side streets) except at major arterial street crossings where the bikeway has a traffic signal.

    I could easily see the turning movements being more dangerous for bikes due to wet, icy or gravel-laden roads.

    Traffic circles are also more dangerous for pedestrians, because the diversion created requires cars (whether driving slowly or quickly) to enter what would ordinarily be the crosswalk between two corners.

    Guest

    February 18, 2013 at 3:19 pm

  7. While I don’t have an scientific evidence to back up my thoughts on this. I can say based on my own observations. That the overall safety of the intersections has vastly improved ever since the traffic circles have been installed.

    If anyone remembers 20-30 years ago before the traffic circles were installed. You had to types of intersections. 1 had no stop signs at all. 2. One road at stop signs. 3 It was a 4-way stop. What I clearly remember is in the case of 1 a lot of drivers would approach it way to fast. There were a few intersections near my house that were netorious for that problem. In the case of 2. A lot of drivers would just speed right through the stop sign. Which made it worse than case 1 because the driver on the cross street would not be aware that another vehicle was coming through.

    It would seem to me there are one of two problems with the current configuration. Poor sight lines. Which would only be improved if the city imposed a bylaw banning corner lots from having certain types of shrubs or fences. Also the banning of parked cars a certain distance from the intersection. The other thing would be to make the traffic circle physically bigger and taking out a bit of each corner. This would force drivers to make more of a turn around the circle instead of trying to cut it straight. Which would cause drivers to slow up.

    Paul C

    February 19, 2013 at 8:16 pm

  8. What you are describing is a properly designed roundabout. Traffic circles do not work, but roundabouts do. The differences may each be small but are collectively very significant. The Manual of Uniform Traffic Control Devices needs to be rewritten.

    Stephen Rees

    February 19, 2013 at 9:20 pm

  9. I wonder if traffic circle safety can be improved if the sign is removed (perhaps replaced by another sign much lower to the ground), and also ensuring that vegetation never gets too high. I have often thought this as I see cars quickly swerve around them and almost hit me.

    Andrew Eisenberg

    February 21, 2013 at 8:09 pm

  10. the sign should be removed …absolutely…for the good reason it is an inept sign:
    It is perfectly legal to make a left turn in front of that sign to turn left…..and it is what is expected from you in most of the case:

    so why not in the example posted by Stephen Rees?

    and let’s be honest: it is also the easiest way to make a left turn (especially on bike).

    so effectively starting by proper signage (European has to come with new sign for round about…probably for good reason), or removing useless signage is the first step:

    The second step, is to tend toward something looking like below:

    Good design rule 1:
    -> The easiest way to make a left turn is to negociate the circle the proper way :
    -> a Good way to achieve that is to have splitter (virtually all european roundabouts have splitter) , which tend to guide and slowdown traffic ahead of the roundabout (and accessory provide a refuge for pedestrian)

    Good design rule 2:
    ->no dangerous obstacle should be in the trajectory of vehicle loosing control – that especially means no edges : a cyclist or motorcyclist can still take it straight -surface make it not comfortable, but if it does, it does little damage.

    The example date from 2011 – and the fruct of many refinement, the design has been improved since with better design for cyclist (here car exiting the roundabout can squeeze cyclist), but still it put the Vancouver roundabout style in the “pre-historic” section.

    Voony

    February 21, 2013 at 10:35 pm

  11. I’d like to see a few more traffic circles in my neighbourhood, including at my kid’s elementary school, where the school bus parking zone and the fire hydrant “no parking zone” should be combined.

    The point I am trying to make is that design must be responsive to the characteristics of place. How many times in 20 years is a fire-hydrant zone occupied by a fire truck at an emergency? And how long does the school bus driver stop (3 minutes max. according to him)? He never leaves the bus, so he’s there to move out in an emergency.

    The same goes for the circle (not the roundabout that—as 8th Ave. & King George; places in France; etc.—cause heavy, heavy congestion at peak times).

    However, in the Vancouver grid the traffic circle is a far better alternative for drivers than four-way stops, two-way stops, or no stop signs at all. The circle occupies the footprint of the collision. It forces drivers to ‘move to the right’. Yeap, they are not without issues. However, they are better than the other three alternatives.

    Bikes and pedestrians need to be taken into account. The crosswalks lie outside the path of travel of the car turning in the circle—that helps.

    And as far as bikes are concerned… sorry, but I don’t feel safe cycling in Vancouver. Advise buying a monthly pass instead and advocating for better transit. The combination of transit and walkability should trump most bike trips once walkability is properly implemented.

    Of course, that’s the big “IF”.

    lewis n. villegas

    February 26, 2013 at 9:46 pm

  12. Well, Lewis, that is a dangerous point of view. The aim here at present is to make cycling feel safer – and this research, conducted in Vancouver, was not about how people who don’t cycle feel, but how people who do cycle – and then get hurt doing it – actually behave. And riding into the centre island of a traffic circle turns out to be one of the causes of injuries. It is as much commentary on these cyclists as it is of the road layout.

    We do not seem to be able to get our heads around the idea that transit should be expanded, and that this will require greater levels of taxpayer support. We also seem to be very reluctant to do any of the things that other places have done that do work to shift people out of cars in cities and into more compatible modes – compatible with urban living that is. Indeed, although most of us live in suburbs, there is still a huge backlash against urbanity. So getting both transit and walkability are, I agree, essential but in the current climate, long shots.

    Vancouver continues its orgy of self congratulation. We spend so much time and effort telling ourselves how well we are doing, we become incapable of improvement.

    Do we actually want to reduce cyclists injuries? Or do we want people to feel safer cycling so they will do more of it?

    Stephen Rees

    February 27, 2013 at 7:50 am

  13. [...] Traffic circles bad: cycle tracks good (stephenrees.wordpress.com) [...]


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