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Bike lanes versus wide curb lanes

Recent blogroll addition the Austin Bike Blog points us to a study on cyclist behavior in bike lanes and wide curb lanes. Years ago, pre-blog and pre-cycling-killing-arthritis, I wrote the following on passing behavior in both facilities which still has some relevance today. Dragging this into the blog so it can be archived and whatnot; original is here. Done with HTML tables, the way God intended! Unfortunately, that doesn't translate so well inside the blog. Any HTML/Movable Type geniuses want to suggest a formatting fix for me here?

One of the most common arguments in bicycle transportation circles stems from the disagreement over whether bike lanes or wide outside lanes provide "better passing distance". Foresterites claim that wide outside lanes are better for a variety of reasons; bike lane advocates come back with the "dedicated space" argument; which Foresterites then attempt to rebut by saying passing distance is "better" in wide curb lanes.

I have direct experience in this matter: my commutes to work generally take me along Shoal Creek Boulevard in north central Austin; which had fairly wide (6'?) bike lanes for several years; and then very wide (19') curb lanes for several more years. I found that a typical 10-pass scenario would go something like the table below. The "distance" given is from car's mirror to where I was riding in approximate center of bike lane.











Passing distance on Shoal Creek Boulevard with Bike Lane Passing distance on Shoal Creek Boulevard with Wide Outside Lane





































1 3.5 ft With minor fluctuation, the typical pass
with the bike lane consisted of the driver giving about half a foot
of distance between their right mirror and the bike lane stripe; thus
providing approximately the same passing space every time. Why does
this happen? Motorists are conditioned in other traffic interactions
to respect lane stripes.
2 3.5 ft
3 3.5 ft
4 3.5 ft
5 3.5 ft
6 3.5 ft
7 3.5 ft
8 3.5 ft
9 3.5 ft
10 3.5 ft







































1 5 ft Some motorists (perhaps even a majority)
provide better passing distance in the wide outside lane scenario
because they are thinking about how much space to give, rather than
letting the lane stripe decide for them.
2 5 ft
3 5 ft
4 5 ft
5 5 ft
6 5 ft
7 4 ft  
8 3 ft  
9 2 ft On the other hand, some other motorists provide considerably
less passing space without the lane stripe to guide them (some from
ignorance; others from antipathy towards cyclists riding in "their
lane").
10 1 ft
Average passing distance from centerline of my bike: 3.5 ft Average passing distance from centerline of my bike: 4.0 ft
10th percentile passing distance: 3.5 ft 10th percentile passing distance: 1 ft

In this dataset, the 30th percentile passing distance for wide outside lanes was worse than for bike lanes; meaning that 3 out of 10 times, the passing distance could be expected to be less for wide outside lanes than it was for bike lanes. (Or, to turn it around, 7 out of 10 times, the passing distance in wide outside lanes would be better than in bike lanes).

Despite the fact that this dataset shows a superior passing distance in 7 out of 10 cases for wide outside lanes, I would choose the bike lane over the wide outside lane in this scenario. I submit that the deciding factor for cyclists, if they are thinking rationally, should not be the average passing distance; since most motorists, whatever the facility, do a fairly good job of providing adequate passing distance. The deciding factor should be the likelihood that motorists who, because they either don't know or don't care, don't provide adequate passing distance. Clearly, in my experience, although average passing distance can be higher in a wide outside lane scenario, the minimum passing distance can at the same time be a lot lower. In this dataset, for instance, I'd argue that the 2 ft and 1 ft passes were close enough to be dangerous (given my width).

This entry was posted in the following categories: Bicycling in Austin

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Comments

Have you seen the (20 MB) PDF from ROMA with their proposed bike/rail/passenger lanes (Appendix 1 which is about halfway down the report). Very interesting stuff.

ftp://ftp.ci.austin.tx.us/DowntownAustinPlan/FINAL11-25-08DAP_Trans_Framework_Report_and_Appendices.pdf

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