LETTERS
Anna Bershteyn is with the Institute for Disease Modeling, Bellevue, WA. Correspondence should be sent to Andres Salomon, Seattle Neighborhood Greenways, 220 2nd Ave S #100, Seattle, WA 98104 (e-mail: [email protected]). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link. This letter was accepted June 23, 2014. doi:10.2105/AJPH.2014.302180
Contributors All authors contributed equally to the letter.
References 1. Graves JM, Pless B, Moore L, Nathens AB, Hunte G, Rivara FP. Public bicycle share programs and head injuries. Am J Public Health. 2014;104(8):e106---e111. 2. Hensley S. Brain injury rate rose in cities after bike-sharing rolled out. NPR.org. Available at: http://www. npr.org/blogs/health/2014/06/12/321332737/braininjuries-rose-in-cities-where-bike-sharing-rolled-out. Accessed June 15, 2014. 3. McKnight Z. 12 VSM, 2013. Bike-share advocates worry Vancouver’s program won’t launch until 2014. Vancouver Sun. Available at: http://www.vancouversun. com/health/Bike+share+advocates+worry+Vancouver+ program+launch+until+2014/8086835/story.html. Accessed June 15, 2014. 4. King County Bike Share Business Plan. 2012. Available at: http://pugetsoundbikeshare.org/wpcontent/uploads/2012/07/KCBS_Business_Plan_ FINAL.pdf. Accessed June 15, 2014. 5. Solomon D. Adult cyclists in Dallas are no longer required by law to wear helmets. Texas Monthly. Available at: http://www.texasmonthly.com/daily-post/adultcyclists-dallas-are-no-longer-required-law-wear-helmets. Accessed June 17, 2014. 6. Proportion of head injuries rises in cities with bike share programs. Washington Post. Available at: http:// www.washingtonpost.com/news/to-your-health/wp/ 2014/06/12/cities-with-bike-share-programs-see-rise-incyclist-head-injuries. Accessed June 15, 2014.
NET EFFECTS OF BICYCLE SHARE PROGRAMS ON BIKE SAFETY Graves et al. examined the association between implementation of a public bicycle share program (PBSP) and the proportion of bicycling-related injuries involving head injury.1 This is an important question because of the absence of helmet requirements in PBSPs. The authors conclude that the proportion of bike injuries involving head injury increased in cities with PBSPs after program implementation, suggesting this is attributable to an increase in the number of bicyclists not wearing helmets. While a rise in the relative rate of head injuries among bike injuries is concerning, the authors neglect to discuss the important finding in their data that the absolute numbers of head
e6 | Letters
injuries and all injuries declined in cities with PBSPs after program implementation. Using the injury counts in the 24-month period before implementation and the 12-month period after implementation, presented in Table 2 of the article, the annual bike injury rate in cities without PBSPs increased by 2% (preimplementation = 1863/2 = 931.5; postimplementation = 953; ratio = 953/931.5 = 1.02). However, in cities with PBSPs, the annual bike injury rate decreased by 28% (preimplementation = 1513/2 = 756.5; postimplementation = 545; Ratio = 545/756.5 = 0.72). This dramatic reduction is an important finding, supporting the conclusion that overall bike safety improves with PBSPs, possibly because of increased driver awareness or improved biking infrastructure. The authors’ key finding was a 30% increase in the odds of head injury after PBSP implementation, but after adjusting for the overall 28% decline in the injury rate in these cities, the likelihood of bike-related head injury decreased by 6% (1.30*0.72 = 0.94.) An additional problem is the use of injury data for all age groups. The authors present a sensitivity analysis using data for only persons aged 15 years and older, and the results are not statistically significant; however, this age group is more appropriate for this research question. The minimum age to use the PBSP in each city included in the study is 16 years, with the exception of Montreal, Quebec, where the minimum age is 14 years.2---6 Although children in some cities may participate with parental permission, these users are likely a small minority of PBSP riders. I agree that the public health community should unequivocally endorse the use of helmets when riding bicycles. However, this analysis suggests that gains in bicycle safety from PBSPs may actually be greater than the added risks of more bicyclists riding without helmets. j Krycia Cowling, MPH
About the Author Krycia Cowling is with the Department of Health Policy and Management, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD.
Correspondence should be sent to Krycia Cowling, 624 North Broadway, Baltimore, MD 21205 (e-mail: kcowlin1@ jhu.edu). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link. This letter was accepted June 27, 2014. doi:10.2105/AJPH.2014.302166
Acknowledgments The author thanks Kay Teschke for helpful discussions.
References 1. Graves JM, Pless B, Moore L, Nathens AB, Hunte G, Rivara FP. Public bicycle share programs and head injuries. Am J Public Health. 2014;104(8):e106---e111. 2. Hubway. Available at: https://www.thehubway. com. Accessed June 20, 2014. 3. DecoBike Miami Beach. Available at: http://www. decobike.com/miamibeach. Accessed June 20, 2014. 4. Nice Ride Minnesota. Available at: https://www. niceridemn.org. Accessed June 20, 2014. 5. Capital Bikeshare. Available at: https://www. capitalbikeshare.com. Accessed June 20, 2014. 6. Bixi Montreal. Available at: https://montreal.bixi. com. Accessed June 20, 2014.
GRAVES ET AL. RESPOND We thank Salomon et al. and Cowling for their interest in our article on head injuries in cities with public bicycle share programs (PBSPs). Because these data were not based on exposure to bicycling (since such data do not exist), we purposely did not focus the analysis on changes in the rates of absolute number of bicycle-related head injuries. Instead, we examined the proportion of injuries to bicyclists that involved a head injury relative to other bicycle injuries. Salomon et al. in fact highlight why we stand by our data: in bike share cities there was a larger decrease in the number of nonhead injured bicyclists than in head injured bicyclists. Although Cowling calls attention to the decrease in the total number of bike injuries in the PBSP cities, her conclusion that bike safety has improved after the institution of the PBSP is not warranted without denominator data. Nor is there foundation for her speculation why the number of bike injuries in these cities may have decreased. Our data are supported by 2 other important pieces of information. Helmets have been shown to decrease the odds of a head injury by as much as 85% in bicyclists involved in a crash,1 and a study published in the Journal in 2012 by Kraemer et al. showed that only 15.7% to 33.1% of Washington, DC, bike share
American Journal of Public Health | November 2014, Vol 104, No. 11
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users wore helmets compared with 68.4% to 70.8% of those riding private bicycles.2 Other studies observed similar patterns.3---6 We agree that the study raises a number of questions that hopefully will be answered in prospectively collected studies. j Janessa M. Graves, PhD, MPH I. Barry Pless, MD Frederick P. Rivara, MD, MPH
About the Authors Janessa M. Graves is with the College of Nursing, Washington State University, and the Harborview Injury Prevention and Research Center (HIPRC), Spokane, WA. I. Barry Pless is with McGill University, and the Injury Prevention Program, Montreal Children’s Hospital, Montreal, Québec. Frederick P. Rivara is with Seattle Children’s Hospital and the University of Washington, Seattle. Frederick P. Rivara is also with HIPRC. Correspondence should be sent to Frederick P. Rivara, MD, MPH, Harborview Injury Prevention and Research Center, Box 359960, 325 Ninth Ave, Seattle, WA 98104 (e-mail: [email protected]). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link. This letter was accepted July 9, 2014. doi:10.2105/AJPH.2014.302215
Contributors All authors contributed equally in all aspects of authorship of this letter and approved the final version submitted for publication.
References 1. Thompson RS, Rivara FP, Thompson DC. A casecontrol study of the effectiveness of bicycle safety helmets. N Engl J Med. 1989;320(21):1361---1367. 2. Kraemer JD, Roffenbender JS, Anderko L. Helmet wearing among users of a public bicycle-sharing program in the District of Columbia and comparable riders on personal bicycles. Am J Public Health. 2012;102(8): e23---e25. 3. Basch CH, Ethan D, Rajan S, Samayoa-Kozlowsky S, Basch CE. Helmet use among users of the Citi Bike bicycle-sharing program: a pilot study in New York City. J Community Health. 2014;39(3):503---507. 4. Bonyun M, Camden A, Macarthur C, Howard A. Helmet use in BIXI cyclists in Toronto, Canada: an observational study. BMJ Open. 2012;2(3):e001049. 5. Fischer CM, Sanchez CE, Pittman M, et al. Prevalence of bicycle helmet use by users of public bikeshare programs. Ann Emerg Med. 2012;60(2):228---231. 6. Grenier T, Deckelbaum DL, Boulva K, et al. A descriptive study of bicycle helmet use in montreal, 2011. Can J Public Health. 2013;104(5):e400---e404.
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Letters | e7
Anna Bershteyn is with the Institute for Disease Modeling, Bellevue, WA. Correspondence should be sent to Andres Salomon, Seattle Neighborhood Greenways, 220 2nd Ave S #100, Seattle, WA 98104 (e-mail: [email protected]). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link. This letter was accepted June 23, 2014. doi:10.2105/AJPH.2014.302180
Contributors All authors contributed equally to the letter.
References 1. Graves JM, Pless B, Moore L, Nathens AB, Hunte G, Rivara FP. Public bicycle share programs and head injuries. Am J Public Health. 2014;104(8):e106---e111. 2. Hensley S. Brain injury rate rose in cities after bike-sharing rolled out. NPR.org. Available at: http://www. npr.org/blogs/health/2014/06/12/321332737/braininjuries-rose-in-cities-where-bike-sharing-rolled-out. Accessed June 15, 2014. 3. McKnight Z. 12 VSM, 2013. Bike-share advocates worry Vancouver’s program won’t launch until 2014. Vancouver Sun. Available at: http://www.vancouversun. com/health/Bike+share+advocates+worry+Vancouver+ program+launch+until+2014/8086835/story.html. Accessed June 15, 2014. 4. King County Bike Share Business Plan. 2012. Available at: http://pugetsoundbikeshare.org/wpcontent/uploads/2012/07/KCBS_Business_Plan_ FINAL.pdf. Accessed June 15, 2014. 5. Solomon D. Adult cyclists in Dallas are no longer required by law to wear helmets. Texas Monthly. Available at: http://www.texasmonthly.com/daily-post/adultcyclists-dallas-are-no-longer-required-law-wear-helmets. Accessed June 17, 2014. 6. Proportion of head injuries rises in cities with bike share programs. Washington Post. Available at: http:// www.washingtonpost.com/news/to-your-health/wp/ 2014/06/12/cities-with-bike-share-programs-see-rise-incyclist-head-injuries. Accessed June 15, 2014.
NET EFFECTS OF BICYCLE SHARE PROGRAMS ON BIKE SAFETY Graves et al. examined the association between implementation of a public bicycle share program (PBSP) and the proportion of bicycling-related injuries involving head injury.1 This is an important question because of the absence of helmet requirements in PBSPs. The authors conclude that the proportion of bike injuries involving head injury increased in cities with PBSPs after program implementation, suggesting this is attributable to an increase in the number of bicyclists not wearing helmets. While a rise in the relative rate of head injuries among bike injuries is concerning, the authors neglect to discuss the important finding in their data that the absolute numbers of head
e6 | Letters
injuries and all injuries declined in cities with PBSPs after program implementation. Using the injury counts in the 24-month period before implementation and the 12-month period after implementation, presented in Table 2 of the article, the annual bike injury rate in cities without PBSPs increased by 2% (preimplementation = 1863/2 = 931.5; postimplementation = 953; ratio = 953/931.5 = 1.02). However, in cities with PBSPs, the annual bike injury rate decreased by 28% (preimplementation = 1513/2 = 756.5; postimplementation = 545; Ratio = 545/756.5 = 0.72). This dramatic reduction is an important finding, supporting the conclusion that overall bike safety improves with PBSPs, possibly because of increased driver awareness or improved biking infrastructure. The authors’ key finding was a 30% increase in the odds of head injury after PBSP implementation, but after adjusting for the overall 28% decline in the injury rate in these cities, the likelihood of bike-related head injury decreased by 6% (1.30*0.72 = 0.94.) An additional problem is the use of injury data for all age groups. The authors present a sensitivity analysis using data for only persons aged 15 years and older, and the results are not statistically significant; however, this age group is more appropriate for this research question. The minimum age to use the PBSP in each city included in the study is 16 years, with the exception of Montreal, Quebec, where the minimum age is 14 years.2---6 Although children in some cities may participate with parental permission, these users are likely a small minority of PBSP riders. I agree that the public health community should unequivocally endorse the use of helmets when riding bicycles. However, this analysis suggests that gains in bicycle safety from PBSPs may actually be greater than the added risks of more bicyclists riding without helmets. j Krycia Cowling, MPH
About the Author Krycia Cowling is with the Department of Health Policy and Management, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD.
Correspondence should be sent to Krycia Cowling, 624 North Broadway, Baltimore, MD 21205 (e-mail: kcowlin1@ jhu.edu). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link. This letter was accepted June 27, 2014. doi:10.2105/AJPH.2014.302166
Acknowledgments The author thanks Kay Teschke for helpful discussions.
References 1. Graves JM, Pless B, Moore L, Nathens AB, Hunte G, Rivara FP. Public bicycle share programs and head injuries. Am J Public Health. 2014;104(8):e106---e111. 2. Hubway. Available at: https://www.thehubway. com. Accessed June 20, 2014. 3. DecoBike Miami Beach. Available at: http://www. decobike.com/miamibeach. Accessed June 20, 2014. 4. Nice Ride Minnesota. Available at: https://www. niceridemn.org. Accessed June 20, 2014. 5. Capital Bikeshare. Available at: https://www. capitalbikeshare.com. Accessed June 20, 2014. 6. Bixi Montreal. Available at: https://montreal.bixi. com. Accessed June 20, 2014.
GRAVES ET AL. RESPOND We thank Salomon et al. and Cowling for their interest in our article on head injuries in cities with public bicycle share programs (PBSPs). Because these data were not based on exposure to bicycling (since such data do not exist), we purposely did not focus the analysis on changes in the rates of absolute number of bicycle-related head injuries. Instead, we examined the proportion of injuries to bicyclists that involved a head injury relative to other bicycle injuries. Salomon et al. in fact highlight why we stand by our data: in bike share cities there was a larger decrease in the number of nonhead injured bicyclists than in head injured bicyclists. Although Cowling calls attention to the decrease in the total number of bike injuries in the PBSP cities, her conclusion that bike safety has improved after the institution of the PBSP is not warranted without denominator data. Nor is there foundation for her speculation why the number of bike injuries in these cities may have decreased. Our data are supported by 2 other important pieces of information. Helmets have been shown to decrease the odds of a head injury by as much as 85% in bicyclists involved in a crash,1 and a study published in the Journal in 2012 by Kraemer et al. showed that only 15.7% to 33.1% of Washington, DC, bike share
American Journal of Public Health | November 2014, Vol 104, No. 11
LETTERS
users wore helmets compared with 68.4% to 70.8% of those riding private bicycles.2 Other studies observed similar patterns.3---6 We agree that the study raises a number of questions that hopefully will be answered in prospectively collected studies. j Janessa M. Graves, PhD, MPH I. Barry Pless, MD Frederick P. Rivara, MD, MPH
About the Authors Janessa M. Graves is with the College of Nursing, Washington State University, and the Harborview Injury Prevention and Research Center (HIPRC), Spokane, WA. I. Barry Pless is with McGill University, and the Injury Prevention Program, Montreal Children’s Hospital, Montreal, Québec. Frederick P. Rivara is with Seattle Children’s Hospital and the University of Washington, Seattle. Frederick P. Rivara is also with HIPRC. Correspondence should be sent to Frederick P. Rivara, MD, MPH, Harborview Injury Prevention and Research Center, Box 359960, 325 Ninth Ave, Seattle, WA 98104 (e-mail: [email protected]). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link. This letter was accepted July 9, 2014. doi:10.2105/AJPH.2014.302215
Contributors All authors contributed equally in all aspects of authorship of this letter and approved the final version submitted for publication.
References 1. Thompson RS, Rivara FP, Thompson DC. A casecontrol study of the effectiveness of bicycle safety helmets. N Engl J Med. 1989;320(21):1361---1367. 2. Kraemer JD, Roffenbender JS, Anderko L. Helmet wearing among users of a public bicycle-sharing program in the District of Columbia and comparable riders on personal bicycles. Am J Public Health. 2012;102(8): e23---e25. 3. Basch CH, Ethan D, Rajan S, Samayoa-Kozlowsky S, Basch CE. Helmet use among users of the Citi Bike bicycle-sharing program: a pilot study in New York City. J Community Health. 2014;39(3):503---507. 4. Bonyun M, Camden A, Macarthur C, Howard A. Helmet use in BIXI cyclists in Toronto, Canada: an observational study. BMJ Open. 2012;2(3):e001049. 5. Fischer CM, Sanchez CE, Pittman M, et al. Prevalence of bicycle helmet use by users of public bikeshare programs. Ann Emerg Med. 2012;60(2):228---231. 6. Grenier T, Deckelbaum DL, Boulva K, et al. A descriptive study of bicycle helmet use in montreal, 2011. Can J Public Health. 2013;104(5):e400---e404.
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