Recent eLetters
Displaying 1-10 letters out of 143 published
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INEQUALITIES IN SIZE AND POWER ACROSS ROAD-USERS
Submit responseAckery et al (1) show that risk to cyclists in collisions with motor- vehicles increases with the size of the motor-vehicle. This evidence may generalize to other types of collisions: consistent with Ackery et al are studies concerning different sizes of automobile with pedestrians (2,4) and collisions concerning different sizes of automobiles in general (3). One can infer that a smaller entity - both in terms of linear dimensions and mass - will likely come off worse than a larger entity. I use the term "entity" to refer to the road-user in conjunction where appropriate with her/his means of conveyance. Thus, the smallest entities are pedestrians and cyclists: larger entities refer to automobiles, pick-up trucks and articulated trucks.
The study of visual perception provides a number of factors regarding size. Time-to-collision is determined from visual expansion of the viewed entity, supplemented by factors such as physical size and the viewer's expectations: a smaller entity entails reduced visual expansion, so would be at risk of overestimated time-to-collision. Also important may be height in the visual field: for example, the driver's height above the road will be greater in a SUV than in a small hatchback. Height affects the upper extent of visual expansion generated by the viewed entity; this is reduced as height increases, so a SUV presents a greater risk than most other private automobiles (4,5).
A second issue concerns the potential power of the entity. A major division follows that for size: the slow speeds and accelerations of self- powered travel contrast with the speeds and accelerations of motor-powered travel. One obvious consequence concerns kinetic energy reflecting both mass and speed: there is a mathematically fourth-power relationship between speed and survivability (6).
The issues of size and power are hardly rocket-science. Yet they often have meagre effects in shaping road safety policy. One example from the UK: any attempts to reduce SUV ownership in urban and suburban areas where the size and power of SUVs are unnecessary in relation to their function have been ineffectual, even given the savings that can be made in a time of increasing fuel prices.
REFERENCES
1. Achery AD, McLellan BA, Redelmeier DA. Bicyclist deaths and striking vehicles in the USA. Inj Prev 2011; 10.1136/injuryprev-1011- 04066l
2. Simms C, O'Neill D. Sports utility vehicles and older pedestrians. BMJ 2005;331:787-788.
3. Eberts RE, MacMillan AG. Misperception of small cars. In RE Eberts, CG Eberts (eds). Trends in Ergonomics/Human Factors II. North Holland: Elsevier 1985;33-40.
4. Stewart D, Cudworth CJ, Lishman JR. Misperception of time-to- collision by drivers in pedestrian accidents. Perception 1993:22:1227- 1244.
5. Cavallo V, Berthelon C, Mestre D, et al. Visual information and perceptual style in time-to-collision estimation. Vision in Vehicles VI. North Holland: Elsevier 1992;81-89.
6. Finch DJ, Kompfner P, Lockwood CR, et al. Speed, speed limits and accidents. Project Report 58. Crowthorne UK: TRL 1994.
Conflict of Interest:
None declared
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Re:Underscoring the Benefits of Cycle Tracks
Submit responseI make brief extra comments in response to Lusk et al.
It is difficult comparing the poor cycle-specific facilities that I find in Northern Ireland with the lack of cycle-specific facilities typical in the US: neither scenario helps cyclists and any statements about which is to be preferred may never be more than impressionistic.
However, I would concede that even imperfect cycle-specific facilities provide publicity for the cause of cycle-commuting. Who knows: if poor facilities lever enough opprobrium among the community, the appropriate authorities may be pressured into acting to upgrade the facilites to something genuinely useful for cyclists.
In contrast, I guess the lack of any cycle-specific facilities typical of the US conveys the impression that urban and suburban cycling is nothing more than an extreme sport for young macho males - it is something to be outlawed if at all possible.
Conflict of Interest:
None declared
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SNAPPING SPEED: THE TOLERATION OF DANGER ON THE ROADS
Submit responseMendivil et al's (1) excellent paper demonstrates the cost-benefits to be derived from investment in speed cameras. It invokes that remarkable Achilles-heel accompanying mass motoring: the toleration of levels of preventable danger that are unacceptable in other transport modes (2).
Attitudes to speed-cameras may reflect the misplaced suspicion that motorists have long directed to the accuracy of their speedometers (3). In the UK, the initial attitude of a considerable section of the motoring public towards speed-cameras was hostile: Cameras were deliberately smashed in the context of a campaign which asserted that speed-cameras were no more than indirect taxation: a cash-cow for government. It was further asserted that overt placement of speed-cameras would lead to erratic speeds which would increase the number and severity of crashes. This problem could of course be alleviated by covert placing of speed- cameras, but this solution was no emollient; it would likely bring about greatly increased detection-rates (4)!
The attitude of the current UK government has unfortunately regressed during the economic downturn: a shift to local decision-making could lead to the reduction or elimination of speed-cameras in some areas. Mendivel et al make it clear that this is not an economically sensible path to follow.
The story of speed-cameras may come to follow the older story of breathalysers: the latter have steadily achieved acceptance by most motorists - but a substantial minority continue stubbornly to misbehave (5). In the meantime, a side-effect of such toleration of danger may be that measures to promote less intrusive and healthier modes of travel - cycling and walking both for full journeys and in conjunction with public transort - remain less effective than they might be in many jurisdictions.
REFERENCES
1. Mendivil J, Gancia-Altes A, Perez K, et al. Speed cameras in an urban setting: a cost-benefit analysis. Inj Prev 2011:10.1136/ip.2010.030882.
2. Reinhardt-Rutland A H. Attitudes to SUVs and "slam-door" rolling stock represent a paradox. BMJ 2005; 331:967.
3. Denton G G. The use made of the speedometer as an aid to driving. Ergonomics 1969;12:447-454.
4. Reinhardt-Rutland A H. Roadside speed-cameras: arguments for covert siting. Police J 2001;74:312-315.
5. Gunay R A, Haran I. Face-to-face interviews with motorists who admit to drink driving in rural Northern Ireland. Traffic Eng Control 2005;46:376-379.
Conflict of Interest:
None declared
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Updating the international research agenda for sports injury prevention research
Submit responseDear Editor
I read with interest Caroline Finch's Online First editorial describing her recent experience of attending and giving a key note address at the third World Conference on Prevention of Injury and Illness in Sport. As someone who also frequently straddles the fields of sports medicine, injury prevention and, more broadly, health promotion, I would like to whole heartedly support Professor Finch's call for greater integration and collaboration across these areas. With sports injury prevention and falls prevention research now on the trail of the holy grail of translational and implementation research, both have so much they can learn from each other and from other fields of health and behavioural science research. Tobacco control is probably the most mature and sophisticated area of health promotion research so why not see what has been learnt there and take what is useful for application in injury prevention. The same applies to physical activity promotion and obesity prevention. Road traffic safety, falls prevention among the elderly, and occupational health and safety are three areas of injury prevention research where so much is already know about what works (and what doesn't) to change safety behaviours and to translate research evidence into real- world reductions in injury mortality and morbidity---yet few sports injury prevention or sports medicine researchers avail themselves of this body of knowledge.
Conflict of Interest:
None declared
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Underscoring the Benefits of Cycle Tracks
Submit responseWe agree with Reinhardt-Rutland's concerns1 about Northern Ireland's poorly designed and policed bicycle facilities but we doubt that the U.S. traditional model of simply treating bicycles as vehicles is better. What works is physically separating bicyclists from fast or heavy motor traffic. Reinhardt-Rutland further suggested that higher fuel costs could effect change where risk assessments have failed. While waiting for increases in fuel prices, we wanted to underscore the benefits of cycle tracks, including their lower injury risk.
Cycle tracks, as described and studied in our paper2 are physically- separated bicycle-exclusive paths along roads as found in the Netherlands. Cycle tracks can have dividers that prevent cars from parking on them. Parallel parked cars alongside a cycle track also separate bicyclists from moving traffic. These cycle tracks by parked cars can also lower exposure of cyclists to air pollution. Unlike a shared-use segregated path, pedestrians have a place on their sidewalk and bicyclists on their cycle track. With cycle tracks, drivers can see a space has been relegated in the right-of-way for bicyclists, especially when it comes with its own red and green bicycle signal.
The Montreal case shows that cycle tracks not only have lower injury risk2 but they may be an effective strategy for promoting cycling3 just by themselves or combined with other policies (ex. public bicycle share program, complete streets, etc.). When successful, drivers can witness women, children, seniors, and parents bicycling instead of mainly young, adult, male bicyclists in the road.
Reinhardt-Rutland wrote that the Northern Ireland's problematic bicycle facilities are often ineffective. By definition, non existent cycle tracks are also ineffective.
1. Reinhardt-Rutland TH. The effectiveness of dedicated cycling facilities: perceived and objective risk. Inj Prev 2011;17(3):216. 2. Lusk AC, Furth PG, Morency P, Miranda-Moreno LF, Willett WC, Dennerlein JT. Risk of injury for bicycling on cycle tracks versus in the street. Inj Prev 2011. 3. Miranda-Moreno LF. Weather or not to cycle: whether or not cyclist ridership has grown: a look at weather's impact on cycling facilities and temporal trends in an urban environment. Transportation Research Record in press.
Conflict of Interest:
None declared
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Time-exposure drowning rate for swimmers
Submit responseMitchell, Williamson and Olivier's (2010) study estimated drowning rates for the Australian state of New South Wales (NSW) in 2005 based on resident population person-time exposure to swimming. The authors state (p. 261) that "failure to adjust injury rates for exposure to a hazard necessarily results in poor estimates of risk", and based on their findings, conclude (p. 264) drowning mortality rates to be "more than 200 times higher than equivalent exposure-adjusted rates for road traffic fatalities." This fact is cited in the Royal Life Saving Society's 2010 National Drowning Report (Royal Life Saving, 2010, p. 3).
However, comparison data detailed below suggest the reported time- exposure drowning rate presents a gross overestimation of swimming risk. This is due to deficiencies in reported numerator data and denominator estimates.
The majority of unintentional drowning death cases included in the reported numerator would be unlikely to come from the population denominator (swimmers). This is a key principle for calculating population rates (Robertson, 2007). Australia-wide unintentional drowning deaths reported for July 2004 to June 2005 identified 97 (37.5%) of 259 victims engaged in a swimming / leisure activity (Royal Life Saving, 2005). In the following 12 month period (2005-2006) this figure was 54 (20.4%) of 265 unintentional drownings (Royal Life Saving, 2006). NSW drowning mortality data, as a subset of national data, would be expected to follow a similar pattern. Mitchell et al. (2010) did not report the numerator frequency for drowning deaths.
Mitchell et al. (2010) report a rate of 90,000 drowning deaths per 10 million hours of swimming in NSW for 2005 (p. 264). The rate indicates that for every thousand hours of swimming at a NSW public pool, river, beach or other location, nine swimmers will drown. But Sydney's Bondi beach alone caters to thousands of bathers most days during summer--yet drowning remains a relatively rare, and not daily, event. Drowning protection at this beach, given the risk of swimming indicated by the reported rate, may be explained by regular surf lifesaver patrols. Even so, the NSW population, which numbers many millions concentrated in coastal areas experiencing a mild to warm climate, will likely spend numerous hours swimming in unpatrolled locations.
The reported rate of 90,000 drowning deaths per 10 million hours of swimming must be questioned given that the annual frequency of drowning among swimmers in NSW is probably well below one-hundred. Fortunately, a check of this rate is readily available using swimming participation data reported by the Australian Bureau of Statistics (2007) for 2005-2006. These data were collected using a method and time period consistent with exposure data relied upon by Mitchell et al. (2010).
In the previous 12 months for Australia (2005-2006), 1,447,300 persons aged 15 and over residing in private dwellings (9% of the national population) were estimated to have participated in organised (13%) or unorganised (87%) swimming. (The swimming participation rate for NSW was estimated by the Australian Bureau of Statistics (ABS) to be marginally higher at 10 percent of the population or 556,400 persons.) For national swimmer estimates in the 12 months prior to sample interview, 1.1 million (76%) reported swimming 53 times or more, 186,300 (13%) 27 to 52 times, 89,500 (6%) 13 to 26 times, and 71,500 (5%) 12 or less times. This estimate equates to a minimum of 64,565,100 swimming episodes in Australia by residents for the 12 month period.
Based on minimum participation frequencies reported by the ABS, I have estimated person-time exposure and drowning rates (using a numerator of 80 drowning deaths while swimming--the average over a five year period to 2006 [Royal Life Saving, 2006]) for mean bathing-time exposures per swimming episode of 30 minutes. The calculation was based on conservative estimates (lowest swimming frequency by frequency group) and ignores what is likely to be millions of bathing hours undertaken by international visitors to Australia (note that drownings of international tourists were included in numerator data). This produced a rate of 24.8 drownings per 10 million hours of swimming. (Note: Mean swimming episodes at 15 minutes yielded a rate of 49.6 and at 60 minutes 12.4, per 10 million hours of swimming.)
Substantial differences between the person time-exposure rate reported by Mitchell et al. (2010) and that listed above (respectively, 90,000 drowning deaths in NSW compared with 25 drowning deaths in Australia, per 10 million hours of swimming) are unlikely to be explained by differences in water exposure or drowning patterns between NSW and other Australian states and territories. Perhaps Mitchell et al. applied sample exposure data in the denominator without extrapolation to the population?
In comparison with reported traffic mortality time-exposure rates, the time-exposure rate of drowning mortality for persons exposed to swimming in Australia appears higher. But rather than being 200 times higher as reported in the study, it's more likely to be a factor below 10.
Mitchell et al. (2010) rightly state (p. 264) that "In terms of policy development, under- or overestimation of the true risk of injury can lead to poor identification of priorities for developing injury prevention policies and interventions, and inadequate resource allocation." The reported rates emphasize the need for precision so as not to perpetuate these challenges to injury problems including drowning.
A spreadsheet with supporting data is available on request.
References cited: Australian Bureau of Statistics (2007). Participation in Sports and Physical Recreation, 2005-06 (cat. no. 4177.0). Canberra: ABS.
Mitchell, R. J., Williamson, A. M., & Olivier, J. (2010). Estimates of drowning morbidity and mortality adjusted for exposure to risk. Injury Prevention, 16(4), 261-266.
Robertson, L. S. (2007). Injury Epidemiology: Research and Control Strategies (3rd ed.). New York: Oxford University Press.
Royal Life Saving (2005). The National Drowning Report 2005. Sydney: Royal Life Saving Society.
Royal Life Saving (2006). The National Drowning Report 2006. Sydney: Royal Life Saving Society.
Royal Life Saving (2010). The National Drowning Reports 2010. Sydney: Royal Life Saving Society.
Conflict of Interest:
None declared
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Critique of: "Risk of Injury for Bicycling on Cycle Tracks Versus in the Street"
Submit responseThe investigators did not meaningfully compare Relative Bicycling Risk and Relative Traffic Danger for individual pairs. Such a comparison of their data demonstrates that the Apparent Cycle Track Effect was increased Danger to bicyclists at two cycle tracks, Neutrality at two cycle tracks, and increased Safety at two cycle tracks. This contrasts with the investigators' claim that the six cycle tracks had a combined 28% lower injury rate than their eight reference streets.
But are the two cycle tracks that are apparently safer in actuality safer for bicycling than their reference streets? Examination reveals that this is false safety.
The investigators assumed, without testing or providing supporting evidence, that Motor Vehicle Occupant injury counts are a surrogate for traffic danger a bicyclist might face on a given street apart from any treatment. Examination of the street characters of Berri and reference Saint Denis show that MVO injuries are not a suitable surrogate for this pairing. I conclude that after adjustment for its reference street being inherently more dangerous for bicyclists, the Apparent Cycle Track Effect of Safety for Berri is instead Unknown.
The Apparent Cycle Track Effect of Safety for Christophe Colomb can be explained by an artificially low Relative Bicycling Risk compared to reference Saint Hubert, and an artificially high Relative Traffic Danger compared to reference Christoph Colomb non-cycle track section. After adjustments I conclude the Christophe Colomb cycle track has Neutrality with both its reference streets.
The reference streets in pairs 1, 3, and 6 are engineered to be more dangerous with the presence of "faux Door Zone Bike Lanes." Simple re- striping to eliminate this hazard and alert bicyclists to the extent of the door zone, and signage to empower them to use a full traffic lane could reduce bicyclist risk on these streets. This would make the cycle tracks comparatively more dangerous.
For my full critique, see: http://bicyclingmatters.wordpress.com/critiques/montreal-cycle-tracks/
Conflict of Interest:
None declared
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THE EFFECTIVENESS OF DEDICATED CYCLING FACILITIES: PERCEIVED AND OBJECTIVE RISK
Submit responseLusk et al's paper (1) indicates an important subtext regarding travel. Governments wish to make personal mobility as widely available as possible; this inevitably entails promotion of the private automobile, which can provide convenient and comfortable travel for the widest range of individuals, including those for whom disability would otherwise pose severe limitations in participating in society. However, there is a competing agenda concerning congestion, sustainability, pollution and health, along with the risk posed by automobiles for vulnerable road-users such as pedestrians and cyclists.
Authorities must strike a balance. In the case of the US, the balance generally favours the automobile: the insistence that cyclists be treated as "operators of vehicles" (2) underlines that assertion. Canada may be more bicycle-orientated. Lusk et al demonstrate that in Montreal segregated cycle tracks can entail fewer casualties than matched common- user roads: the consequent reduction in perceived and objective risk can sussessfully act to promote cycling.
0However, poorly designed and policed facilities may render the situation for cyclists worse than if the US model is followed. This is arguably the case in Northern Ireland. Cycle lanes at the side of roads are provided. Despite official prohibition, motor-vehicles frequently park or straddle cycle lanes before undertaking manoeuvres: junctions are particularly problematic regarding rights-of-way. Finally, cycle lanes are often well short of any meaningful journey. The official stance is that: "Use of cycle lanes is not compulsory and will depend on your experience and skills" (3). So cyclists are free to use other traffic lanes - but motorists seem unaware of this and often evince hostility towards cyclists exercising this freedom. The cyclist is uncomfortable on any part of the road - hardly a recipe for the development of mass cycle-commuting.
Segregated paths are also provided. These are in fact shared with pedestrians. Pedestrians no doubt provide better fellow travellers for cyclists than do automobiles, but the two groups are nevertheless incompatible regarding speed: cycling through groups of pedestrians or walking through streams of cyclists is not comfortable. Curiously, this is recognised regarding sidewalks, which are solely for pedestrians: cycling and driving are officially outlawed (3).
The above issues may reflect anomalous conceptualisations of risk. Northern Ireland again provides a useful example. The political conflict ("the Troubles") was always perceived to be particularly dangerous - for more so than the roads - as reflected in provision of manpower and resources. In fact, Northern Irish roads were objectively much riskier. Throughout the worst of the Troubles in the 1970s and 1980s, the objective risks of politically-motivated death and injury were about 50% and 12% respectively those for the roads (4). It is perhaps not surprising that strategies for promoting cycling are often ineffectual. With obvious exceptions such as the Netherlands, Denmark and - perhaps - Montreal, this unfortunately may apply in many jurisdictions.
Perhaps the seemingly inexorable increases in fuel cost may achieve real change: personal economics may win where conceptualisations of risk have failed.
References
1. Lusk A C, Furth P G, Morency P, et al. Risk of injury for bicycling on cycle tracks versus in the street. Inj Prev doi: 10.1136/ip.2010.028696.
2. Forrester J. Effective cycling. Cambridge: MIT Press, 1984.
3. The Highway Code: AA Publishing, 2008.
4. Reinhardt-Rutland A H. Roadside speed-cameras: arguments for covert siting. Police J 2001; 74: 312-315.
Conflict of Interest:
None declared
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Re:Re:Zero Blood Alcohol Concentration (BAC) Limit for drivers under 21
Submit responseThe major problem in enforcing the zero BAC limit is ensuring that the province or territory enacts accompanying legislation authorizing the police to demand a breath sample from drivers subject to this limit. There has been no problem with drivers testing positive with exceedingly small amounts of alcohol in their breath samples, because of natural processes or diet. Presumably, the machines have thresholds to eliminate this problem.
Conflict of Interest:
None declared
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Re:Zero Blood Alcohol Concentration (BAC) Limit for drivers under 21
Submit responseHow easy is it to enforce zero limit in the face of possiblity of physicigical sources of alcohol and uses of other dietry and household sources of alcohol? There might be a lot or few false positive cases as a result. Is there anything of in the scientific evidence base?
Conflict of Interest:
None declared
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