Monday, April 19, 2010

TED Talks - Intersections

Reader Jamie sent us a link to a great presentation that is part of the TED Talks series. South Fraser OnTrax has been following traffic safety from day one, and one thing that makes intersections safer are roundabouts. In fact, a signalized intersection (traffic light) is the most dangerous type of intersection. The following the presentation talks about the safety improvement from installing roundabouts including how they can drop fatal crashes by 90%. Roundabouts also save fuel which is good for the environment. The presenter goes one step further and talks about changing the way three-way intersections works. I suggestion that you check out this 4 minutes clip.


Bregalad said...

Roundabouts are a great idea for cars, but in my experience they are an impassable death trap for cyclists and pedestrians.

The whole point of a roundabout is keeping traffic moving. The whole point of a cross walk is to stop traffic. The two are mutually exclusive.

When approaching a roundabout or small traffic circle the driver will continue to move unless (s)he notices a competitor for the roundabout at which point (s)he may yield or merely slow so as to determine whether the other party is yielding. At no point is something small and slow like a bike or pedestrian considered a competitor for the space and therefore is subconsciously ignored.

How do you reconcile the desire to put pedestrians and cyclists first with the fact that roundabouts are designed to exclude and/or kill them?

Joe Zaccaria said...

I would argue that roundabouts and cross walks are not mutually exclusive. In the past what was termed a "roundabout" was far from today's modern engineered roundabout.

A modern roundabout is engineered for the hierarchy of users that start with pedestrians and cyclists and then cars and trucks.

The pedestrians and cyclists are served firstly in the roundabout by high viability. Crosswalk starts are placed in clear areas or fitted with bulged curbs. There are also yield signs on all sides to calm traffic. The internal circle also facilitates trucks. These are some basics of a modern roundabout.

Nathan Pachal said...

Don't be fooled about the "safety" of a signalized intersection. Drivers turning right into pedestrians is the number one way that pedestrians die in BC. Joe has touched on the safety feature of high-visibility crosswalks before the entrance of a roundabout.

Please check out this video:

Here is another presentation on roundabout safety for pedestrians:

As for cycling, the above link states:

"In general, it seems that collisions involving bicyclists are reduced somewhat with roundabouts particularly in severity..."

There are also some cool designs to reduce the vehicle/bicycle conflict even further.,%20carrerotondes.jpg

Bregalad said...

My experience is mostly with traffic circles, the small roundabouts that Vancouver is fond of installing on its bicycle routes and neighbourhoods adjacent to arterials. I have almost no experience with roundabouts on arterial roads as a substitute for signals.

The first priority for traffic circles in Vancouver is ensuring there are large, view blocking signs indicating which way to go around them. After that residents insist they be beautified with all manner of plant life and additional signs indicating which organization is responsible for maintaining the garden. The result often looks nice, but makes it even harder to see what's happening on the other side. Children and pets are invisible behind many Vancouver traffic circles. At typical Vancouver side street speeds it's impossible for cars to stop in time to avoid colliding with any object that's not seen when approaching the circle.

There are many traffic circles in my area and I've been watching pedestrian and vehicle behaviour at them for years. I confidently state the following:
- Pedestrians would rather cross mid-block than at a traffic circle.
- There is obvious fear in the eyes of pedestrians walking near a traffic circle.
- Many cars treat traffic circles as highway barriers and frequently go faster around the circle than they do on the narrow side streets leading into and out of the circle. This is amplified when two cars are approaching from opposite directions. Often the street has barely enough space for them to pass, but the traffic circle gives each his own lane.