Shared lane marking
A shared-lane marking or sharrow is a street marking installed at locations in Australia, Canada, and the United States. This marking is placed in the center of a travel lane to indicate that a bicyclist may use the full lane.
According to the US Manual on Uniform Traffic Control Devices, shared-lane markings are used to:
- Assist bicyclists with lateral positioning in a shared lane with on-street parallel parking in order to reduce the chance of a bicyclist’s impacting the open door of a parked vehicle;
- Assist bicyclists with lateral positioning in lanes that are too narrow for a motor vehicle and a bicycle to travel side by side within the same traffic lane;
- Alert motorists of the lateral location bicyclists are likely to occupy within the traveled way;
- Encourage safe passing of bicyclists by motorists; and
- Reduce the incidence of wrong-way bicycling.
These markings are used in the USA, Australia and other countries. In US usage, the wide shape of the arrow, combined with the bike symbol, gave rise to unofficial names such as "bike in a house" or "sharrow". In the UK roughly the same function is served by a bicycle symbol without arrows. However this tends to be used more as an indication of a formal cycle route rather than as an encouragment to share the road.
The original "bike in a house" or "man jumping barrels at home" marking was developed by James Mackay and included in the 1993 Denver Bicycle Master Plan. While Mackay had considered a "connect the dots" pavement markings approach for bicycle route definition and lane positioning reinforcement for bicyclists earlier when he was the Bicycle Facilities Engineer for the North Carolina Department of Transportation, the City of Denver's unwillingness to commit to bike lane markings meant that shared lane markings were the only pavement marking treatment for bicyclists that the City would implement. The hollow arrow surrounding the bicyclist was intended to reinforce the correct direction of travel for bicyclists (who were frequently observed riding the wrong-way, against traffic, in Denver).
In 2004, the city of San Francisco, California began experimenting with the shared lane marking, and developed a revised symbol consisting of a bicycle symbol with two chevron markings above the bicycle.
In a 2009 paper, Northeastern University researcher Peter G. Furth proposed the "Bicycle Priority Lane", which combines sharrows with dotted lines inside the usual lane markings. This marks a five-foot-wide zone in the center of the lane which bicyclists are encouraged to use. The city of Boston, Massachusetts began experimenting with these markings in 2013.
Behavioral studies have shown that streets with shared lane arrows increase separation between motor vehicles and bicyclists, encourage cyclists to ride outside the door zone, and may reduce wrong-way cycling and sidewalk cycling, which are associated with increased crash risk.
However, another study based on hospital records shows no statistically significant reduction in injuries, and possibly a small increase.
Based on the San Francisco experimental data, in August 2004 the California Traffic Control Devices Committee (CTCDC) approved the use of this marking in California. In the 2009 edition of the Manual on Uniform Traffic Control Devices, shared lane markings were approved for general use. The city of Seattle, Washington included extensive use of shared lane markings in its Bicycle Master Plan of early 2007. The concept has since been implemented by cities throughout the United States.
- 23rd Streetscape Project, City of Richmond website, access date December 28, 2008
- Manual on Uniform Traffic Control Devices, Part 9, Traffic Control for Bicycle Facilities, 2009, 
- San Francisco Bay Bikers blog entry on San Francisco Chronicle site
- 1993 Denver, Colorado Bicycle Plan
- e-mail from James Mackay to John S. Allen, May 21, 2011
- "San Francisco's Shared Lane Pavement Markings: Improving Bicycle Safety", February 2004
- Peter G. Furth (2009-01-08). "Bicycle Priority Lanes: A Proposal for Marking Shared Lanes". Retrieved 2013-12-01. Alternate URL
- Martine Powers (2013-11-20). "Starts and Stops: New ‘sharrows on steroids’ debut on Allston’s Brighton Ave.". Boston Globe.
- "Evaluation of Shared Lane Markings". Federal Highway Administration. October 2010. Retrieved Feb 27, 2013.
- Alta Planning and Design (February 2004). "San Francisco's Shared Lane Pavement Markings: Improving Bicycle Safety". San Francisco Department of Parking & Traffic. Retrieved Feb 27, 2013.
- "Comparing the effects of infrastructure on bicycling injury at intersections and non-intersections using a case–crossover design". 14 December 2012.
- CTCDC Minutes, August 12, 2004
- "9C. 7". Manual on Uniform Traffic Control Devices, Chapter 9. Federal Highway Administration. 2009.
- "Two more weeks to comment on city bike plan", Seattle Post-Intelligencer, May 4, 2007
- ATSSA webpage on MUTCD experimentation & interpretation letters
- Christopher deWolf. "Follow the sharrows." Spacing Montreal, August 29, 2007
- "Sharrows, shared use markings"
- "Red de carriles bici"
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