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Publication Number: FHWA-HRT-10-041
Date: December 2010
Evaluation of Shared Lane Markings
CHAPTER 1. INTRODUCTION
Shared lane markings (also referred to as sharrows) help convey to motorists and bicyclists that they must share the roads on which they are operating. The purpose of the markings is to create improved conditions for bicyclists by clarifying where they are expected to ride and to remind motorists to expect bicyclists on the road. In the absence of bicycle lanes, motorists often neglect to safely share travel lanes with bicyclists, which can compel bicyclists to ride closer to parked motor vehicles. Such a scenario can result in a dooring crash if someone opens a vehicle door as the bicyclist passes. Also, when bicyclists stay to the far right in narrow travel lanes, passing motorists often track too closely to the bicyclists. This can be unnerving for bicyclists, leaving little margin for error, and sometimes leading to crashes.
In 2008, a recommendation was made by the National Committee on Uniform Traffic Control Devices (NCUTCD) to include shared lane markings in the next version of the Manual on Uniform Traffic Control Devices (MUTCD).(1,2) That recommendation was made with limited research conducted on an 11-ft spacing from the center of a shared lane marking to the curb.(3) A literature review uncovered no additional research on other spacing options. The 2009 edition of the MUTCD includes provisions for shared lane markings, specifically the sharrow design, with guidance that the markings should be placed at least 11 ft from the curb face or the edge of pavement on a street with parallel parking. Further, on streets with no parking and an outside lane less than 14-ft wide, the centers of the sharrows should be placed at least 4 ft from the curb or the edge of pavement.(1)
The purpose of this study was to evaluate the impact of several uses of shared lane markings, specifically sharrows, on operational and safety measures for bicyclists and motorists. The following hypotheses were explored for sharrows:
A technical drawing of the sharrow marking is depicted in figure 1.
Figure 1. Illustration. Specifications for the sharrow from California MUTCD 2010.
The original bike-in-house design that has been used or slightly modified in other locations for some time is shown in figure 2. This design was used in Gainesville, FL, in a wide curb lane situation and was previously evaluated by the Highway Safety Research Center (HSRC). It was found that the markings increased the safety margin for bicyclists riding near the curb. Additionally, sidewalk riding decreased.(4)
Figure 2. Photo. Bike-in-house marking.
The bike-in-house marking was modified to a bike-and-chevron marking, and the two designs were evaluated in San Francisco, CA. Superior results were associated with the bike-and-chevron marking shown in figure 3.(3) Based on feedback from bicyclists and motorists, the pitch on the chevrons was subsequently increased to resemble more of a directional guide. Given the results of the evaluation, the bike-and-chevron marking was added to the existing 2003 California Manual on Traffic Control Devices through a policy directive in September 2005.(5) Additional evaluation detail is provided in chapter 2 of this report.
Figure 3. Photo. Bike-and-chevron marking.
NCUTCD issued a technical committee recommendation in January 2005 that proposed adding a shared lane marking section to part 9 of the MUTCD.(1,2) Afterward, the Bicycle Technical Committee of the NCUTCD recommended that this proposal be sent to the Federal Highway Administration (FHWA) in January 2007. The proposal suggested that shared lane markings should be used to prevent bicyclists from being struck by opened doors of parked motor vehicles (commonly referred to as dooring). Furthermore, it was recommended that the markings be placed 11 ft from the curb to encourage bicyclists to track over the markings and increase the distance between bicyclists and the door zone.
At the beginning of the project, HSRC staff contacted communities who had expressed interest in evaluating different uses of sharrows. Staff visited Cambridge, MA; Portland, OR; and Seattle, WA, as well as local officials in Chapel Hill, NC. Based on the site visits, they sent a memorandum to FHWA recommending the following sharrow evaluations:
These recommendations were accepted by FHWA, and this report describes the sharrow evaluations for each location.
The actual design of the sharrow has been evolving, and figure 1 reflects the design used in Cambridge, MA, and Chapel Hill, NC. In Seattle, WA, a version that was a few inches longer was created and used in the evaluation. Figure 4 illustrates a generic sharrow as it appears in the 2009 version of the MUTCD.(1)
Figure 4. Illustration. Generic version of a sharrow.
Topics: research, safety, pedestrians and bicyclists, lane markings
Keywords: research, safety, pedestrians and bicyclists, shared lane markings, sharrows, bicycles
TRT Terms: research, safety, pedestrians and bicyclists, traffic control devices, road markings, lane lines