Researchers suggest that there is a need for far more rigorous research to understand the impacts of bicycle treatments (DiGioia et al., 2017). One of the main issues facing researchers who study bicycle infrastructure is the availability of accurate bicycle volume counts and the current dependence on crash data. The Highway Safety Manual (HSM) includes quantitative, crash-based outcome measures that are not reflective of the near-miss accidents or users levels of comfort. Safety measures suggested through the HSM are therefore examined in terms of an increase or decrease in crash rates. Staff has reviewed and collected a variety of resources to help educate ourselves and others on existing research related to bicycle safety through design, diving beyond the standards presented in the HSM.
After the release of the National Association of City Transportation Official's (NACTO) 2nd Edition of the Urban Bikeway Design Guide, NACTO released a document entitled Contextual Guidance for Selecting All Ages & Abilities Bikeways. This document includes a chart that allows individuals to see the recommended Bicycle Facilities, based on the following factors:
- Target Motor Vehicle Speed
- Target Motor Vehicle Volume
- Motor Vehicle Lanes
- Key Operational Considerations (pedestrians, curbside activity level, etc.)
An example of how the chart operates is demonstrated below:
- Target Motor Vehicle Speed: <10 mph
- Target Motor Vehicle Volume: 1,000 to 2,000
- Motor Vehicle Lanes: No center lane, or single lane one-way
- Key Operational Considerations:Pedestrians share the roadway
- All Ages & Abilities Bicycle Facility: Shared Street
The above-discussed resource was released as a subsequent publication to the 2014 Urban Bikeway Design Guide. Note that in 2014, the California Department of Transportation (Caltrans) officially endorsed NACTO's Urban Street Design Guide and Urban Bikeway Design Guide as valuable tools for designing and constructing safe infrastructure.
In addition to the Guidance by NACTO, Staff reviewed a 2014 Master's Thesis by Jonathan E. DiGioia of Georgia Institute of Technology entitled "Safety Impacts of Bicycle Infrastructure: A Critical Review." This research has since been published by the Journal of Safety Research (2017, Vol. 61). DiGioia's study examined literature related to 22 different types of bicycle treatments, synthesized the findings, and data sources used in the findings. While this research reiterates the need for more studies to be conducted, it does offer some key findings; see below:
- Bike Box treatments: A study showed a 400-500% increase in drivers yielding to cyclists after a bike-box treatment, and 76% motorist compliance with not encroaching in the bike box.
- Bike Lanes: Study shows bike lanes result in significantly less wrong-way riding than merely “wide curb lanes”; three older studies found decreases in crash risk with bike lanes.
- Buffered Bike Lanes: No quantitative studies found dealing with crash / injury / conflict outcomes relating to buffered bike lanes; cyclist volumes increase 77-271% after installation of buffered bike lanes; a study in Portland, OR saw overwhelming preference by bicyclists for buffered bike lanes and stronger sense of protection from motorized traffic and less worry of being “doored” by a parked car.
- Colored (Green) Bike Lanes: Survey of drivers and cyclists showed positive perceptions of increased safety by both parties when colored bike lanes were present.
- Cycle Track: Study found 28% lower injury crash rate on streets with cycle tracks versus streets without; a different study noted that one-way cycle tracks appear to be safer at intersections than two way cycle tracks.
- Increase bicycling levels in community (eyes on the street philosophy) – Findings are that injury rates decrease with increased levels of walking and bicycling.
Safety research on the effects of bicycle infrastructure is an on-going, nationwide project. Educating ourselves and others on current research and publications is a crucial step for increased knowledge and education on the topic. Staff intends to continue to bring reports and academic literature to the Bicycle and Pedestrian Facilities Advisory Committee as further studies are released.