Posted by Jonathan Maus (Publisher/Editor) on December 29th, 2009 at 11:21 am
In our coverage of the new bike boulevard on Spokane Street in Sellwood many of you have shared questions and concerns about the new "channelizer" islands that have been installed. The islands are meant to channel motor vehicle and bike traffic into specific areas at intersections to avoid pinch-point conflicts, but several readers have said they don't plan on using them and others say they actually increase danger for people on bicycles.
Here's how one commenter responded to them:
These channelizers are wonderful until you hit one at night and crash your bike and break your ribs. Like I did. What the hell are they supposed to do? I’ve been using this street for years and nobody warned me that someone would be pouring twenty tons of concrete in my path.
Greg Raisman with the City of Portland Bureau of Transportation has heard these concerns and he responded with a lengthy comment about them. In the comment, Raisman explains, in detail, the City's rationale for channelizers (and why PBOT prefers them over traffic circles). It's a bit wonky, but also highly informative (emphasis mine):
"The channelizers were based on designs seen in Utrecht, The Netherlands and developed in conversation with traffic safety specialists from Utrecht. In addition, they are a very common traffic calming element in residential settings throughout the rest of The Netherlands.
The basic answer is that they are a device that slows the speed of motor vehicle traffic by narrowing the travel lanes for cars. In general, motor vehicle speed is slowed in one of two ways. Either through "vertical deflection" where you send the vehicle over something like a speed bump. Or, through "horizontal deflection" where you introduce a curve in the travel line. In addition, "oppositional friction" can be used to slow speed as often happens on narrow residential streets in Portland (we often refer to the situation as courtesy queuing).
In the past, we've had two basic devices to slow speed on a residential street. Speed bumps, which are the most effective tool available to slow speed, and residential traffic circles.
The residential traffic circles are often considered a popular device because they are pretty. However, they have not proven to be very effective at addressing the safety concern from speed. That's why you will see some segments with traffic circles having speed bumps added (like on SE Lincoln or NE 53rd). Those new speed bumps are in place because the traffic circles did not bring the speed down to the desired travel speed.
The other problem with traffic circles is that they cause a very uncomfortable pinch point when a person on a bicycle and a person driving a car arrive at the circle at the same time. They are designed to have one vehicle go through at a time. However, when you have a driver that tries to pass while traversing the circle, it creates a very uncomfortable condition that can compromise safety, particularly for children or seniors.
On occasion, people who have not experienced this condition question whether it's a real problem. My suggestion is always to take a bike ride on NE 7th from Broadway to Alberta. There are a series of traffic circles on that road and exposure to motor vehicle traffic is high enough that you are sure to experience the issue. When you do, imagine you're traveling with an 8-year-old child or an adult who is a new, novice rider. This condition happens less often on successful boulevards because of the lower volumes of motor vehicle traffic. However, when it does happen, it's a problem.
In addition to not achieving desired speed reductions and causing pinch points, traffic circles are also quite expensive to install and have very high maintenance needs. Without proper maintenance, they can cause intersection visibility problems.
The channelizer produces a similar speed reduction benefit to a traffic circle by both narrowing the roadway and creating a courtesy queuing situation for cars. However, they present a bicycle rider with an option if they arrive at the same time as a motor vehicle traveling down the street. The bicycle rider can travel through the middle of the device at any time. But, if there is a car approaching at the same time, they can take the channel and have physical separation between them and the car as they travel through the intersection. This is particularly useful for children and seniors who often react in less predictable ways when facing more stressful traffic conditions. In addition, they are lower cost to install and have maintenance needs that are many orders of mangnitude lower than a traffic circle.
There are two of the channelizers in place. One at 7th and one at 15th. In addition to reducing speed, the one placed at 7th is to gently encourage motorists leaving Oaks Park to turn and continue their trip on Tacoma. A traffic barrier was not installed here because there was a need to allow motor traffic to continue eastward to 13th to be able to access the signal at 13th and Tacoma if they are heading eastbound. So, the soft-barrier approach with the channelizer was used to send the cue to turn. We do not expect all east bound travelers to turn because of this treatment. However, we believe there will be some increase in the turning movement in our after measurements.
The channelizer at 15th is in place to pay particular focus on reducing speed at the Sellwood Community Center. The combination of the new speed bump in front of the Center with the channelizer on the east side of the intersection should make this location acheive the lowest travel speed of any location on the corridor. In addition, St. Agnes School is one block to the north at 15th and Miller. The islands help create a shorter crossing distance for children that are walking to that school.
These are the only two channelizers that are currently slated to be installed. There are no additional examples on any of the remaining 7 bike boulevards that will be built by the end of June 2010.
If they are successful at reducing speed and provide the desired operational effects, it's possible they would be considered on future projects. All of these decisions would be discussed as part of open houses that are always held and publicized when new bike boulevards are in the design phase."
For more information about this and other bike boulevard projects, visit the City's website.Email This Post Possibly related posts