Wednesday, April 20, 2011

Burrard Bridge comparisons part two

My last post talked about the traffic management issues that, at one level, illustrate why the Burrard St. Bridge is not a good model for critics promoting a "two lane solution" for our own Blue Bridge.  I've added a few more pics and some commentary at my flickr site to illustrate further some of the engineering challenges that should add another nail to that coffin.

Burrard has more width to work with and the separated bike lane has been installed using concrete barriers to provide some distance between cyclists and fast moving traffic.  The facility is designed to provide single direction bike lanes, with the east side sidewalk converted to bicycle only use and pedestrians assigned the west side sidewalk on the bridge.  This will prevent conflict in the confined space on the bridge, something that would be a serious problem if the bike lane was two-way or worse, multi-use, an idea that has been suggested by critics looking for "solutions" to save the Blue Bridge.  Some may profess an interest only in providing a substitute for the loss of acces to the now closed rail bridge for cyclists and pedestrians, but I believe that many are simply looking again to find some way to demonstrate that a "solution" exists that would allow the city to save the bridge while providing improvements for cyclists and pedestrians.

The photos should provide some food for thought on how much more constrained we would be on the Johnson St. Bridge, as compared to Burrard, where we have lanes that are narrower and the functional needs of a movable bridge can't accommodate the significant additional weight of an effective barrier system.

The need for robust separation would be particularly acute if a two-way or multi-use lane were to be contemplated.  While daylight is generous through spring and summer and into early fall, commute times across the bridge will be cloaked in darkness for many months of the year and bicycles in particular, riding against the flow of traffic on the bridge, would need some signficant separation from opposing traffic and blinding lights.  Engineering standards for multi-use or two way facilities adjacent to roadways demand more space than would be available on the Johnson St. Bridge where a standard dimension "jersey barrier" would rob at least two feet from the separated lane.

It's another example of where the math doesn't work.  The city's response so far has been to strengthen the visual cues for drivers to slow down and share the road across the bridge, and to encourage cyclists to "take the lane" to ensure safe passage.  It is a safer and more effective way of calming traffic and providing an adequate, if not ideal, level of service for everyone who will be using the bridge over the next 3 1/2 years while we work on our replacement structure.


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