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Advisory Bicycle Lanes
This article is based on a March, 2009 APBP ListServe thread. Roger Geller, Portland's (Ore.) Bicycle Coordinator, asked about this type of facility because Portland contemplates installing perhaps as much as 42 miles of advisory bike lanes. Thanks to APBP members Tom Bertulis, John Ciccarelli, Peter Furth, and Dwight Kingsbury for their contributions.
What's an advisory bicycle lane? Also called a "non-compulsory bicycle lane” or "suggestion lane” (translated from the Dutch "suggestiestrook”), it’s a bicycle lane into which motor vehicles may legally encroach. Therefore, the line demarcating the lane is dashed instead of solid. An advisory bicycle lane is often—but not always—used in conjunction with centerline removal.
Generally, a mandatory bicycle lane is preferable; an advisory bicycle lane should only be used when a mandatory lane cannot be used. Advisory bicycle lanes should be considered 1) when street width is inadequate for mandatory bike lanes or 2) where cars are likely to encroach on a bike lane as it approaches a bike box. Advisory bike lanes should not be used where they are likely to be blocked by parked motor vehicles.
Advisory bike lanes in conjunction with centerline removal on roads with substandard width are common across Europe and are generally well received by cyclists. For example, a 24-foot roadway with a center stripe may be re-striped to provide two six-foot advisory bike lanes and a 12-foot center travel lane (the stripes are dashed). Motorists may enter the bicycle lanes in order to negotiate oncoming traffic, but only when the lanes are not occupied by cyclists.
In Suffolk County, England, re-striping a substandard road with advisory bike lanes resulted in reduced car traffic and increased cycling. From 2005 to 2006, ADT decreased from 5,600 cars per day to 4,500 cars per day while bike usage rose from 150 cyclists per day to 183 cyclists per day. There has been only one crash in the last four years (it involved a motorcyclist going too fast and no other vehicles were involved).
Advisory lanes may also be used on multi-lane streets and streets with centerlines. Tom Bertulis points out one issue with these applications: "I worked in Glasgow for three years, and even though Glasgow has an impressive 120 km cycle network, all the bike lanes are advisory bike lanes. There are no mandatory bike lanes in that city. That means cars can—and do—park in the lanes, which is a hassle for cyclists. A sharrow is preferable if the car parking can’t be removed.”
Commenting on the recommended width for advisory bicycle lanes, Bertulis notes: "I must say I take issue with the size of the advisory lane in some studies. One study showed advisory bike lanes whose width varied from 3.7 to 4.3 feet and the study from Denmark [Narrow cross sections without centre line markings - "2 minus 1" rural road; Trafitec, June 2007] shows that only 85 cm (2.8 feet) are left on the side for cyclists. Motorists tend to hug white lines, and if 85 cm are left for the cyclist, the motorist will try to pass at that distance. In Scotland we discussed this issue at length. It turns out that the Cyclist Dynamic Envelope (CDE) is 2.5 feet and Dutch studies conducted by CROW have shown that cyclists need a buffer of 2.5 feet minimum to sustain levels of comfort. Consequently, five feet (1.5 m) is the minimum width we would recommend for advisory cycle lanes. The cars can still encroach on the lanes if there are no cyclists, but when there are cyclists they will give the full five feet of space.”
There is as yet little data on the crash rates for advisory bicycle lanes. A four-year study from Wiltshire County (England) showed a 35 percent drop in motor vehicle crashes along the roadways where the centerline was removed. Discussing an evaluation of a German application, Dwight Kingsbury says, "Crash results didn’t show any strong advantage or disadvantage; annual cyclist crash rates were low at test and comparison sites with or without the marking of advisory lanes.”
References and resources:
In his paper Bicycle Priority Lanes: A Proposal for Marking Shared Lanes (January 2009), Peter Furth discusses "negotiating for the bike zone boundary” and proposes the use of sharrows in conjunction with advisory bike lane striping. https://myfiles.neu.edu/xythoswfs/webui/_xy-5474320_1-t_9UyJB6TN
New Type of Layout for 60 km/h Rural Roads. SWOV (Netherlands), 2007. http://www.swov.nl/rapport/Factsheets/UK/FS_Driving_strips.pdf
van der Kooi, R.M. and A. Dijkstra. Some Behavioural Effects of Non-Compulsory (Bicycle) Lanes on Narrow Rural Roads. SWOV (Netherlands), 2003. (In Dutch, with English language summary). http://www.swov.nl/rapport/R-2003-17.pdf
The UK’s Local Transport "Note” on Cycle Infrastructure Design describes advisory cycle lanes in section 7.3. http://www.dft.gov.uk/pgr/roads/tpm/ltnotes/ltn208.pdf
Herrstedt, L. Narrow cross sections without centre line markings - "2 minus 1" rural road. Road user behaviour study. Trafitec (Denmark), June 2007. http://www.trafitec.dk/pub/Summary%20note%20-%202%20minus%201.pdf