The health risks and benefits of cycling in urban environments compared with car use: health impact assessment study

BMJ 2011; 343 doi: http://dx.doi.org/10.1136/bmj.d4521 (Published 4 August 2011)
Cite this as: BMJ 2011;343:d4521

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Dear Editor,

This study did not take into account important morbidity associated with cycling.

As potential health risks, only road traffic incidents and exposure to air pollution were included.

Genitourinary tract injuries, pudendal nerve entrapment, erectile dysfunction, infertility in both men and women(!), priapism, penile thrombosis, hematuria, torsion of spermatic cord, prostatitis, perineal nodular indurations, elevated serum PSA levels, were not even mentioned. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]

Studies have demonstrated that a high percentage of cyclists are affected by all these pelvic symptoms.

Failing to include all this cycling-associated morbidity has compromised Authors' final conclusions, regarding the amount of health risks associated to cycling, in my opinion.

References

[1] Sports Med. 2011 Jun 1;41(6):463-76. doi: 10.2165/11588740- 000000000-00000. Effects of bicycle saddle height on knee injury risk and cycling performance. Bini R, Hume PA, Croft JL. Sport Performance Research Institute New Zealand, School of Sport and Recreation, Auckland University of Technology, Auckland, New Zealand.

http://www.ncbi.nlm.nih.gov/pubmed/21615188

[2] Urologe A. 2011 Feb;50(2):188-96. Influencing of the PSA concentration in serum by physical exercise (especially bicycle riding). Kindermann W, Lehmann V, Herrmann M, Loch T. Institut fur Sport- und Praventivmedizin, Universitat des Saarlandes, Campus, Gebaude B8.2, 66123 Saarbrucken, Deutschland.

http://www.ncbi.nlm.nih.gov/pubmed/21246346

[3] J Sex Med. 2010 Oct;7(10):3424-33. doi: 10.1111/j.1743- 6109.2010.01905.x. Association between attributes of a cyclist and bicycle seat pressure. Bressel E, Nash D, Dolny D. Biomechanics Laboratory, Utah State University, Logan, UT 84322, USA.

http://www.ncbi.nlm.nih.gov/pubmed/20626598

[4] J Sex Med. 2010 Jul;7(7):2346-58. Epub 2010 Jan 19. Bicycle riding and erectile dysfunction: a review. Sommer F, Goldstein I, Korda JB. Department of Urology, Institute of Men's Health, University Medical Centre Hamburg-Eppendorf, Hamburg, Germany.

http://www.ncbi.nlm.nih.gov/pubmed/20102446

[5] Curr Urol Rep. 2007 Nov;8(6):491-7. Bicycle riding, perineal trauma, and erectile dysfunction: data and solutions. Goldstein I, Lurie AL, Lubisich JP. San Diego Sexual Medicine, Alvarado Hospital, 6655 Alvarado Road, San Diego, CA 92120, USA.

http://www.ncbi.nlm.nih.gov/pubmed/18042330

[6] BJU Int. 2007 Jan;99(1):135-40. Digital three-dimensional modelling of the male pelvis and bicycle seats: impact of rider position and seat design on potential penile hypoxia and erectile dysfunction. Gemery JM, Nangia AK, Mamourian AC, Reid SK. Department of Radiology, Dartmouth-Hitchcock Medical Center, Lebanon, NH 03756, USA.

http://www.ncbi.nlm.nih.gov/pubmed/17227499

[7] J Sex Med. 2005 Sep;2(5):612-9. Only the nose knows: penile hemodynamic study of the perineum-saddle interface in men with erectile dysfunction utilizingbicycle saddles and seats with and without nose extensions. Munarriz R, Huang V, Uberoi J, Maitland S, Payton T, Goldstein I. Institute for Sexual Medicine, Department of Urology, Boston University School of Medicine, 720 Harrison Avenue, Suite 600, Boston, MA 02118, USA.

http://www.ncbi.nlm.nih.gov/pubmed/16422818

[8] J Sex Med. 2005 Sep;2(5):596-604. Bicycle riding and erectile dysfunction: an increase in interest (and concern). Huang V, Munarriz R, Goldstein I. Institute for Sexual Medicine, Department of Urology, Boston University School of Medicine, 720 Harrison Avenue, Boston, MA 02118, USA.

http://www.ncbi.nlm.nih.gov/pubmed/16422816

[9] J Urol. 2004 Aug;172(2):637-41. Erectile dysfunction after a long-distance cycling event: associations with bicycle characteristics. Dettori JR, Koepsell TD, Cummings P, Corman JM. Department of Epidemiology, School of Public Health and Community Medicine, University of Washington and Department of Urology, Virginia Mason Medical Center, Seattle, USA.

http://www.ncbi.nlm.nih.gov/pubmed/15247750

[10] Eur Urol. 2005 Mar;47(3):277-86; discussion 286-7. Epub 2004 Dec 30. The vicious cycling: bicycling related urogenital disorders. Leibovitch I, Mor Y. Department of Urology, Meir Medical Center, Affiliated to Sackler School of Medicine, Tel Aviv University, 59 Tchernichovski st., Kfar Saba, Israel.

http://www.ncbi.nlm.nih.gov/pubmed/15716187

[11] J Appl Physiol. 1984 Jun;56(6):1453-63. Endurance training effects on plasma hormonal responsiveness and sex hormone excretion. Bullen BA, Skrinar GS, Beitins IZ, Carr DB, Reppert SM, Dotson CO, Fencl MD, Gervino EV, McArthur JW.

http://www.ncbi.nlm.nih.gov/pubmed/6735803

Competing interests: None declared

Stavros Saripanidis, Consultant in Obstetrics and Gynaecology in Greece

Private Sector, 55131

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Evaluating the benefits of public bicycle schemes needs to be undertaken carefully: Response from the authors.

We set out to estimate the health impacts of the Bicing system and started with the assumption that 90% of the Bicing users previously made the same trip by car, and conducted further (sensitivity) analyses using other scenarios of mode shift (assuming that 9.6% of Bicing users came from cars, 55.1% from public transport and 26.1% from walking) (1) (see web appendix). As mentioned in the paper, they made little difference to the results (10.46 vs 12.46 deaths avoided for the main driver of the analyses physical activity), thus not changing the main message of the paper. In our analyses we found that there may be greater benefits from walking compared to cycling, and reported an increase of 0.61 deaths in the Bicing population from those who previously walked for 2km on a regular basis and shifted to Bicing for the same amount of travel.

Traffic incidents mortality: author's response

We found that the difference in traffic incidents between cyclists and car drivers was less than reported in UK(2), possibly because we did the calculation of risk for an urban area and not the whole country (resulting in less miles travelled and fewer deaths). Cycling mortality reported in Barcelona (and used in this study) was very low (5 deaths in the last 9 years) resulting in a low comparative risk between cycling and driving. We conducted sensitivity analyses using the higher traffic mortality rates reported by De Hartog(3) and found little impact on our final results.

Table. Traffic fatalities rate in bike and car (deaths per billion kilometres travelled).

Reference List

1. Rojas-Rueda D, de Nazelle A, Tainio M, Nieuwenhuijsen MJ. The health risks and benefits of cycling in urban environments compared with car use: health impact assessment study. BMJ 2011;343:d4521.

2. Department for Transport. Reported Road Casualties Great Britain 2009. 2010. London, UK, Transport Statistics Publications.

3. De Hartog JJ, Boogaard H, Nijland H, Hoek G. Do the health benefits of cycling outweigh the risks? Environ.Health Perspect. 2010;118:1109-16.

Competing interests: None declared

David Rojas-Rueda, predoctoral researcher

Audrey de Nazelle researcher and Mark J Nieuwenhuijsen research professor

Center for Research in Environmental Epidemiology, Barcelona, Spain

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The authors wrongly assume that the majority of the users of this scheme switched from car driving, invalidating many of their claims.

What surprises me most are the relatively similar mortality rates quoted in this study for cyclists and car drivers. In Britain in 2009 the relative death rates per billion miles travelled were 34 v 2.8 (cyclists v car drivers)- a 12 fold difference.

http://www2.dft.gov.uk/adobepdf/162469/221412/221549/227755/rrcgb2009.pdf

Competing interests: None declared

William P Soutter, Gynaecologist

Imperial W12 0HS

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I spent some of May/June this year studying the health benefits and risks of inner-city cycling, and I am pleased to see that your paper supports my findings. These bicycle hire schemes are a move in the right direction for encouraging bike use. This said, in the UK the main barrier people have in relation to cycling, is not the lack of bicycles, but the lack of safe cycle lanes. The only way that we can present cycling as a safe alternative to car use is if segregated cycle lanes are built. Countries such as The Netherlands and Denmark which have a developed cycling infrastructure show safe and habitual bike use. UK Government interventions so far have been for the most part ineffective, as much of the money is invested in less effective 'attitude-changing' schemes. If the UK is to become a pedal-powered nation then investment must go towards building a cycle-friendly infrastructure which offers an environment where it is safe to cycle. The budgets that go towards building cycle lanes should not reflect the number of people that currently cycle, but the number of people we want to see cycling.

Competing interests: None declared

Colin W. Primrose, Medical student

The University of Glasgow

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This paper sets out to compare the health benefits of the Bicing scheme (Barcelona's public bicycle share scheme) with possible risks associated with increased bicycle riding. The key variables used by the researchers include physical activity, exposure to air pollution and road traffic injury. The authors rightly identify that although traffic congestion is often a major motivator behind the establishment of public bicycle share schemes (PBSS), the health benefits may well be the largest single benefit of such schemes. Certainly PBSS appear to be one of the most effective methods of increasing the number of bicycle trips across a population, providing additional transport options and improving awareness of the possibilities bicycles offer urban transport systems.

As noted by the authors Rojas-Rueda, de Nazelle, Tainio, & Nieuwenhuijsen (2011), the number of PBSS have increased rapidly over recent years, yet little work has been undertaken to evaluate their impacts (Buttner et al., 2011; Shaheen, Zhang, Martin, & Guzman, 2011). Whilst Rojas-Rueda et al. (2011) should be commended for undertaking what is understood to be amongst the first health impact assessment on a PBSS, flawed assumptions regarding the proportion of Bicing users who have substituted a motor vehicle journey invalidates their results. Put simply, their assumption that between 90% and 100% of Bicing users would have made the trip by car had it not been for the PBSS dramatically overstates the actual rate of trip substitution. The available data demonstrates only 9.6% of Bicing trips are substituting for a car journey (City of Barcelona, 2007). Moreover, 6.3% of trips taken on Bicing were previously private bicycle journeys - neutralising any benefit to public health.

In addition to overstating the health benefits, this erroneous assumption by Rojas-Rueda et al. (2011) has also led to overstated environmental benefits of the Bicing scheme. For instance, the authors state "As a result of journeys by Bicing, annual carbon dioxide emissions were reduced by an estimated 9,062,344kg" (p. 1). Further: "Data on shifts in mode of travel as a result of the Bicing initiative could not be found" (p. 3). Data published by Anaya & Bea (2009), collected by the City of Barcelona show users of the Bicing scheme to be substituting from other modes of transport in the following proportions: Public transit 55.10%, motor vehicle 9.60%, walking 26.10%, private bike 6.30% and new trip 2.80%.

As the above figures illustrate, over one quarter of Bicing trips are replacing pedestrian journeys, and given the evidence suggesting walking trips have twice the health benefit of bicycle riding, on a per kilometre basis (New Zealand Transport Agency, 2009), the results produced by Rojas- Rueda, et al. (2011) likely overstate the health benefits of the scheme.

In addition to these aforementioned assumptions regarding the proportion of Bicing trips replacing car journeys, the total number of daily trips using Bicing also appears higher than what the available evidence suggests. The authors calculate that there are 28,251 Bicing members using the scheme daily and assume a 90% shifting from car journeys. Assuming 28,251 members use the scheme daily and 90% substituting for car use (despite evidence to the contrary), this equates to 25,426 users substituting car for Bicing. Assuming these users take two trips per day, 50,852 journeys would be made by these users. These numbers, used by the authors to determine the health benefit of the Bicing scheme conflict with the data made available by the operators (City of Barcelona, 2011) suggesting something closer to 33,000 trips per day (6000 bikes used 5.5 times per day). Even this lower figure is quite possibly higher than the actual figure, given that it is very rare for all 6000 bicycles to be in circulation at the one time.

Only those trips previously undertaken by car, as well as the 2.8% of new trips generated by Bicing should be included in the physical activity benefits of the Bicing scheme. One should also factor the health benefit lost from the pedestrians opting for Bicing, given that the literature widely regard walking to have twice the physical activity benefit of cycling on a per kilometre basis (Fishman, Ker, Garrard, & Litman, 2011; New Zealand Transport Agency, 2009). Although these assumptions made by the authors are the central flaw in the study approach, the sensitivity analysis that assumed only 10% of Bicing trips were replacing a car trip is much closer to the reality of the Bicing system, although there are no reported calculations for this analysis.

The authors have assumed that 90% of Bicing users were new to cycling when they signed up. If this was the case, it might be possible that these new cyclists have a higher road traffic injury rate than regular cyclists, yet this is omitted from the results and discussion, despite the authors using road traffic injury as one of the key measures of health impact.

The carbon dioxide emission savings stated by the authors, previously highlighted as artificially high, also fail to take into account the redistribution and manufacture of the bicycles. Most PBSS use petrol or diesel powered trucks to move their bicycles through the system and the Bicing system is no different in this regard. The manufacture of 6000 bicycles, as well as their docking stations is not without significant carbon dioxide emissions, and whilst it may well be less than the savings as a consequence of reduced car use, it must still be factored into the equation.

When calculating the health risks posed by road traffic injury, the study only uses mortality and this fails to capture serious injuries, which can be significant.

The study would have provided a valuable assessment of the benefits to risk of the Bicing system had it taking more realistic assumptions of the level to which the system was replacing motor vehicle use.

In the concluding comments, the authors note that the Bicing scheme has successfully increased the number of people cycling in Barcelona - to a much greater degree than other initiatives in the past. An unsubstantiated claim made by the authors suggests the Bicing scheme is "low cost", yet no mention of Bicing's cost is used in the paper. Similarly, the authors conclude that other cities should follow Barcelona in creating "cost saving" transport initiatives - yet no benefit cost analysis was undertaken in order to determine if the scheme produces a net economic benefit.

Despite the assumptions compromising the findings of this study, the authors made a number of insightful points that have not been widely published in the literature on PBSS. Firstly, the authors highlight the potential for bicycle trips to replace car trips of greater distance (people choose closer destinations when they are solely under human power). Secondly, Bicing and other PBSS might be the catalyst for increasing the acceptability and legitimacy of cycling, which could act as a catalyst for more cycling generally - even outside of the scheme. With PBSS proving popular not just in continental Europe, but also in cities in the UK and the US, it appears these innovative, public transport options may help increase physical activity, reduce air and noise pollution and reduce traffic congestions. Measures aimed at increasing the substitution rates from car journeys will maximise these benefits.

Overall, the paper is a useful addition to the literature, in that it has attempted to assess the health benefits of a large scale PBSS and weighed these against potential risks related to cyclists exposure to air pollution and road traffic injuries. Unfortunately a fundamentally flawed assumption related to the proportion of Bicing trips replacing car journeys invalidates the results of this paper. A future paper with up to date data would create a significant contribution to this emerging area within the field of sustainable transport.

References

Anaya, E., & Bea, M. (2009). Cost-benefit evaluation of Bicing. Paper presented at the ECOMM Conference, San Sebastian/Donostia, Spain. http://www.epomm.eu/ecomm2009/6_bea.pdf

Buttner, J., Mlasowsky, H., Birkholz, T., Groper, D., Fernandez, A. C., Emberger, G., . . . Banfi, M. (2011). Optimising Bike Sharing in European Cities: A Handbook: Intelligent Energy Europe program (IEE).

City of Barcelona. (2007). The City Council extends Bicing services Retrieved from http://w3.bcn.cat/multimedia/fitxers/premsa/070925mesbicing.590.pdf

City of Barcelona. (2011). Bicing Press Release. Barcelona: City of Barcelona.

Fishman, E., Ker, I., Garrard, J., & Litman, T. (2011). Cost and health benefit of active transport in Queensland. Brisbane: Produced for Queensland Government.

New Zealand Transport Agency. (2009). Economic Evaluation Manual (Volume 2) (pp. 276): New Zealand Transport Agency.

Rojas-Rueda, D., de Nazelle, A., Tainio, M., & Nieuwenhuijsen, M. J. (2011). The health risks and benefits of cycling in urban environments compared with car use: health impact assessment study. British Medical Journal.

Shaheen, S., Zhang, H., Martin, E., & Guzman, S. (2011). Hangzhou public bicycle: Understanding early adoption and behavioural response to bike sharing in Hangzhou, China. Paper presented at the TRB Annual Meeting, Washington D.C. http://76.12.4.249/artman2/uploads/1/Hangzhou_Public_Bicycle.pdf

Competing interests: None declared

Fishman, PhD Scholar

Centre for Accident Research and Road Safety - Queensland, Australia

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Cycling is probably the future of urban transport with inherent advantage of being ecofriendly and healthy transport medium. Rojas-Rueda D et al observed that public bicycle sharing initiatives are good for health(1). Authors studied three primary outcome measures viz. all cause mortality for the physical activity, air pollution and road traffic accident mortality for their study. These three outcome measures are inadequate to study the true benefits and risks of cycling. Non fatal cycle accidents and other bicycle use related ailments are equally important parameters for unbiased assessment of benefits of cycling. In United States the average annual cost of nonfatal bicycle injuries in children and youth aged 0 to 19 was $4.7 billion for the year 2008(2). Bikers often suffer musculoskeletal injuries, more commonly due to wear and tear and bad posture. An old fashioned bicycle that allows one to sit upright in a balanced position is often very difficult to find now a days. Modern racing type bicycles encourage a forward bent, flexed position to maximize speed. Such posture places excessive stress on the low back, neck, shoulders, elbows and the wrists. Prolonged extension posture of head fatigues the muscles of the neck. Neck pain, back pain, knee pain, handlebar neuropathies, plantar fasciitis, Achilles tendonitis etc are also not uncommon among the cyclists(3). There is increased risk of Erectile Dysfunction associated with cycling which is further increased by poor design of the seat(4). Thus further in depth studies are required to assess the health consequences of switching to the cycling. Policy decisions of such large extent effecting millions of people should be based on hard facts not just popular perception. Further, policymakers need to take proper steps to minimize cycling related injuries like using appropriate type and design of the bicycles and educating people about the healthy way of biking.

References

1. Rojas-Rueda D, de Nazelle A, Tainio M, Nieuwenhuijsen MJ. The health risks and benefits of cycling in urban environments compared with car use: health impact assessment study. BMJ. 2011;343:d4521.

2. Sheppard, M. A., & Taylor, D. Medical, work loss, and quality of life costs for fatal and hospital-admitted bicycle injuries to children 0-19 in 2004 dollars [unpublished data]. Calverton, MD: Pacific Institute for Research and Evaluation.

3. Thompson MJ, Rivara FP. Bicycle-related injuries. Am Fam Physician. 2001 May 15;63(10):2007-2014.

4. Sommer F, Goldstein I, Korda JB. Bicycle riding and erectile dysfunction: a review. J Sex Med. 2010 Jul;7(7):2346-2358.

Competing interests: None declared

Naveen Dutt, Senior Resident

Kirti Chaudhry

Govt. Medical College & Hospital, Chandigarh, India

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