Cycle helmet

A bicycle helmet is a helmet intended to be worn while riding a bicycle. They are designed to attenuate impacts to the head of a cyclist in falls while minimizing side effects such as interference with peripheral vision. They are specified to withstand simple falls onto a flat surface without other vehicles being involved.

A cycle helmet should be light in weight and should provide adequate ventilation, because cycling can be an intense aerobic activity which significantly raises body temperature and the head in particular needs to be able to regulate its temperature.

How they work
There are two main types of helmet: hard shell and soft/micro shell (no-shell helmets are now rare). In both types impact energy is absorbed as a stiff foam liner is crushed, up to the point where the liner is crushed to its minimum thickness, or the helmet shatters, after which no further energy is absorbed. Collision energy varies with the square of impact velocity: a typical helmet will absorb the energy of a fall from a stationary or slow-moving bicycle, an impact speed of around 12mph. It will only reduce the energy of a 30 mph impact to 27.5 mph, and even this will be compromised if the helmet fails. This energy calculation is based on the standards, which take no account of the weight of the rider's body.

As a subsidiary effect they also spread point impacts over a wider area of the skull. Hard shell helmets do this better, but are heavier and less well ventilated. They are more common among stunt riders than road riders or mountain bikers. Additionally, the helmet will reduce superficial injuries to the scalp. Hard shell helmets may also reduce the likelihood of penetrating impacts although these are very rare.

The key component of most modern bicycle helmets is a layer of expanded polystyrene (EPS), the same type of plastic used for packaging and insulation of cool boxes. This material is sacrificed in an accident, being crushed as it absorbs a major impact. Bicycle helmets should always be discarded after any accident.

Helmets are most effective in straight line, or linear, blows to the head at moderate speed. Helmets are not well designed to deal with high speed impacts or rotational stresses (crashes that are not centred, and involve rotation of the head). They are not designed to provide adequate protection for a collision involving another moving vehicle, (e.g. a car).

A common misunderstanding is to assume that a broken helmet has prevented some serious injury. Helmets are designed to crush without breaking; EPS absorbs little energy in brittle failure and once it fails no further energy is absorbed.

History
Prior to the mid-1970s, the dominant form of helmet was the leather "hairnet" style, mainly used by racing cyclists. This offered minimal impact protection and acceptable protection from scrapes and cuts. In countries with long traditions of utility cycling, nearly all cyclists did not and still do not wear helmets. The use of helmet by non-racing cyclists began in the U.S. in the 1970s. After many decades of where cycles were regarded as children's toys, many American adults took up cycling during and after the bike boom of the 1970s. Two of the first modern bicycle helmets were made by MSR, a manufacturer of mountaineering equipment, and Bell Sports, a manufacturer of helmets for auto racing and motorcycles. These helmets were a spinoff from the development of expanded polystyrene (EPS) foam liners for motorcycling and motorsport helmets, and had hard polycarbonate plastic shells. The bicycle helmet arm of Bell was split off in 1991 as Bell Sports, having completely overtaken the motorcycle and motor sports helmet business.

The first commercially successful purpose-designed bicycle helmet was the Bell Biker, a polystyrene-lined hard shell released in 1975. At the time there was no appropriate standard; the only applicable one, from Snell, would be passed only by a light open-face motorcycle helmet. Over time the design was refined and by 1983 Bell were making the V1-Pro, the first polystyrene helmet intended for racing use. In 1984 Bell produced the Li'l Bell Shell, a no-shell children's helmet. These early helmets had little ventilation.

1985 saw the introduction of Snell B85, the first widely-adopted standard for bicycle helmets; this has subsequently been refined into B90 and B95 (see Standards below). At this time helmets were almost all either hard shell or no-shell (perhaps with a vacuum-formed plastic cover). Ventilation was still minimal due mainly to technical limitations of the foams and shells in use.

Around 1990 a new construction technique was invented: in-mould microshell. A very thin shell was incorporated during the moulding process. This rapidly became the dominant technology, allowing for larger vents and more complex shapes than hard shells.

Hard shells declined rapidly among the general cyclist population during the 1990s, almost disappearing by the end of the decade, but remain popular with BMX riders as well as inline skaters and skateboarders.

The late 1990s and early 2000s saw advances in retention and fitting systems, replacing the old system of varying thickness pads with cradles which adjust quite precisely to the rider's head. This has also resulted in the back of the head being less covered by the helmet; impacts to this region are rare, but it does make a modern bike helmet much less suitable for activities such as unicycling, skateboarding and inline skating, where falling over backwards is relatively common. Other helmets will be more suitable for these activities.

Helmet regulations in cycling sport
Historically, road cycling regulations set by the sport's ruling body, Union Cycliste Internationale (UCI), did not require helmet use, leaving the matter to individual preferences and local traffic laws. The majority of professional cyclists chose not to wear helmets, citing discomfort and claiming that helmet weight would put them in a disadvantage during uphill sections of the race.

The first serious attempt by the UCI to introduce mandatory helmet use in 1991 was met with strong opposition from the riders. An attempt to enforce the rule at the 1991 Paris-Nice race resulted in riders' strike, forcing the UCI to abandon the idea.

While voluntary helmet use in professional ranks rose somewhat in the 1990s, the turning point in helmet policy was the March 2003 death of Kazakh Andrei Kivilev. Some officials within UCI had been trying to re-establish a helmet rule, and used this incident to push through the change, initially claiming that it was for insurance reasons although the insurers subsequently denied this. The new rules were introduced on May 5, 2003, with the 2003 Giro d'Italia being the first major race affected. The 2003 rules allowed for discarding the helmets during final climbs of at least 5 kilometres in length; subsequent revisions made helmet use mandatory at all times.

There is no evidence that injuries have reduced as a result and an informal count of serious and fatal injuries kept by cycle safety advocate Bob Davis indicates that more riders were killed in the five years 2000-2005 than in any previous decade.

Standards

 * ''See also: Cycle helmet timeline

In the United States the Snell Memorial Foundation, an organization initially established to create standards for motorcycle and auto-racing helmets, implemented one of the first standards. The American National Standards Institute (ANSI) created a standard called ANSI Z80.4 in 1984. Later, the United States Consumer Product Safety Commission (CPSC) created its own mandatory standard for all bicycle helmets sold in the United States, which took effect in March 1999.

In the UK the currently applicable standard is EN 1078:1997, which replaces BS 6863:1989.

The CPSC and EN1078 standards are lower than the Snell B95 (and B90) standard; Snell helmet standards are externally verified, with each helmet traceable by unique serial number. EN 1078 is also externally validated, but lacks Snell's traceability. The most common standard in the US, CPSC, is self-certified by the manufacturers. It is generally true to say that Snell standards are more exacting than other standards, and most helmets on sale these days will not meet them (no current Bell brand helmet is Snell certified, some Specialized ones are – the Snell Memorial Foundation website includes a list of certified helmets).

In 1990 the Consumers' Association (UK) market survey showed that around 90% of helmets on sale were Snell B90 certified. By their 1998 survey the number of Snell certified helmets was around zero. Hard shells declined rapidly among the general cyclist population over this period, almost disappearing by the end of the decade, but remained more popular with BMX riders as well as inline skaters and skateboarders.

Although helmet standards have weakened over time there is no data on which to base an assessment of how this has affected the design goal of mitigating minor injuries. Minor injuries are substantially under-reported and it is difficult if not impossible to effectively measure such injuries on a meaningful scale.

The major source of serious injury to cyclists is impact with motor vehicles. Current helmet standards are inadequate to protect against such collisions, the energies involved are routinely in excess of the rated capacity of the best motorsport helmets. Helmets designed to higher standards have generally not sold well, while helmets designed to even lower standards have sold well. A helmet's ability to absorb energy could be improved by increasing the volume of polystyrene, but this would make it thicker, heavier, and hotter to wear. The trend is towards thinner helmets with many large vents. This trend to lower standards has been noted in some of the studies It is relatively common for helmets to fail on test, and some helmets on sale are not certified to any accepted standard. The most widely-cited pro-helmet studies were conducted when most helmets were of a hard-shell construction; these are now rare outside of niche applications such as BMX.

Most of the standards are designed to be passable using current designs and materials rather than to set a certain minimum safety standard. Tests typically involve weighting the helmets and dropping them onto anvils with flat, hemispherical and cornered (comparable to a kerbstone) shapes. Since the hemispherical and cornered anvils present the most difficult tests to pass, they are tested with a shorter drop, although this has no evident basis in actual accidents.

Proper fit
It is important that a helmet should fit the cyclist properly – according to research most (well over 90%) helmets have been found to be incorrectly fitted. Efficacy of incorrectly fitted helmets is reckoned to be much lower, one estimate states that risk is increased threefold.

Most manufacturers provide a range of sizes ranging from children's to adult with additional variations from small to medium to large. The correct size is important. Some adjustment can usually be made using different thickness foam pads. Helmets are held on the head with nylon straps, which must be adjusted to fit the individual. This can be difficult to achieve, depending on the design. Most helmets will have multiple adjustment points on the strap to allow both strap and helmet to be correctly positioned. Additionally, some helmets have adjustable cradles which fit the helmet to the occipital region of the skull. These provide no protection, only fit, so helmets with this type of adjustment are unsuitable for roller skating, stunts, skateboarding and unicycling.

The helmet should sit level on the cyclists head with only a couple of finger-widths between eyebrow and the helmet brim. The strap should sit at the back of the lower jaw, against the throat, and be sufficiently tight that the helmet does not move on the head. It should not be possible to insert more than one finger's thickness between the strap and the throat.

Research evidence


Evidence for the efficacy of helmets in preventing serious injury is contradictory and inconclusive. In general, analyses of the relative merits of different bike safety interventions put helmets low down, because no helmet will reduce the probability of crashing (and there is some evidence that helmets may increase this likelihood). Proactive measures including bike maintenance and riding skills are far more important. Although the link is not causal, it is observed that the countries with the best cycle safety records (Denmark and the Netherlands) have among the lowest levels of helmet use. Their bicycle safety record is generally attributed to public awareness and understanding of cyclists, education, and to some extent separation from motor traffic.

The evidence comes from two main types of observational study:
 * case-control studies, in which cyclists who have injured their heads ("cases"), and cyclists who have not ("controls"), are compared. Such studies consistently find that cases report a lower rate of helmet-wearing than controls. This has been taken as strong evidence that cycle helmets are beneficial in a crash and that all cyclists should wear them. Known problems with this study design include confounding (attributing benefits from differences in behaviour to differences in helmet choice), and reporting errors (people falsely reporting helmet use). The most widely-quoted case-control study, by Thompson, Rivara, and Thompson, reported an 85% reduction in the risk of head injury by using a helmet. There are many criticisms of this study, including use of an inappropriate control group.  This study includes clear evidence that, in a population with voluntary wearing, the profile of non-head injuries is very different between helmeted and unhelmeted cyclists, an effect first documented by Spaite et al.:


 *  Population studies compare changes in helmet use and injury rates in a single population over time, most notably where helmet laws have resulted in large changes in a short time. A review of jurisdictions where helmet use increased by 40% or more following compulsion showed no measurable change to the proportion of head injuries among injured cyclists. The largest study, covering eight million cyclist injuries over 15 years, showed no effect on serious injuries and a small but significant increase in risk of fatality. Weaknesses of this type of study include: simultaneous changes in the road environment (e.g. drink-drive campaigns); inaccuracy of exposure estimates (numbers cycling, distance cycled etc.).

Different analyses of the same data can produce different results. For example, Scuffham analysed data on the New Zealand helmet law in 1995 and concluded that, after taking into account long-term trends, the laws had no measurable effect. His subsequent re-analysis without accounting for the long-term trends showed a small benefit. Re-analysis of the Thompson, Rivara and Thompson data substituting helmet wearing rates from co-author Rivara's contemporaneous street counts, reduces the calculated benefit to below the level of statistical significance. Another analysis of the source data from this study showed a 70% reduction in lower limb injuries from helmet use. One problem with all analyses is that the population of injured cyclists is generally very small, and it is difficult to collect sufficient incidents to form a statistically significant sample.

The definition of injury is also open to debate, and injury figures are acknowledged to be inaccurate. Research by TRL and others shows that reporting of injuries is related to severity: fatal injuries are almost always reported, in the developed world, but 90% or more of lesser injuries go unreported. Helmets are most likely to be effective against lesser injuries. Pro-helmet studies routinely refer to prevention of traumatic brain injury, which has connotations of permanent intellectual disablement, but where sufficient data is provided it is found that the majority of the brain injuries in these studies are concussion. A study of fatally injured cyclists found injuries of fatal severity to multiple organ systems were in sixteen of twenty riders, including six with no significant head injury. Four riders died of fatal injury to head alone and one of these was the only rider known to be wearing a safety helmet. His death resulted from a fall from a bicycle at moderate speed rather than collision with a motor vehicle.

Recent research on traumatic brain injury adds further confusion, suggesting that the major causes of permanent intellectual disablement and death may well be torsional forces leading to diffuse axonal injury (DAI), a form of injury which helmets cannot mitigate. Helmets may increase the torsional forces by increasing the distance from the extremities of the helmet to the centre of the spine, compared to the distance without a helmet.

Much of the research is partisan in one way or another. Thompson, Rivara and Thompson were already committed advocates of helmet legislation before publishing their first study; their report for the Cochrane review has also been criticised for being dominated by their own work. Rodgers, who showed helmets to be associated with increased risk of fatality, was replying to criticism of CPSC for focusing on bicycle design and manufacture standards. One report concluding a 60% reduction in injuries was found to be in error due to a simple statistical error; correcting the error results in a claimed efficacy of 186%; despite this the authors continue to assert that the results stand. A report commissioned by the UK Government was supportive of cycle helmet promotion but dismissed out of hand much of the contradictory evidence, and the principal authors were associated with a programme of the Child Accident Prevention Trust (CAPT), which is strongly pro-helmet. Curnow, author of papers on helmets and traumatic brain injury, has also published criticism of pro-helmet research.

The helmet debate
There is a long-running argument over the use, promotion, and compulsion of cycle helmets. Most heated controversy surrounds laws making helmet use compulsory, particularly regarding the substantial disparity between claimed injury savings in small-scale prospective studies (e.g. Thompson, Rivara and Thompson, 1989) and later, more comprehensive studies, particularly from jurisdictions which have used compulsion to substantially raise helmet use over a very short period. Helmet use in New Zealand, for example, rose from 43% to over 95% in under three years, with no measurable change in head injury rates (Scuffham, 1997).

Controversy is fuelled by support given to the pro-compulsion movement by Bell Sports in particular, and by the fact that many of the most vocal proponents of helmets are not themselves cyclists.

Various organizations have taken up definite positions on the issue, not always based on a full review of the evidence. For example, the British Medical Association used to be against helmet compulsion, following an extensive review of the evidence in 1999. In late 2004 the BMA's Board of Science and Education adopted a 'position' calling on the UK government to introduce cycle helmet legislation, and this was confirmed at the 2005 Annual Representative Meeting following fifteen minutes of debate (transcript). The BMA's new position uses statistics provided by the British political lobby group, the Bicycle Helmet Initiative Trust, and excludes from consideration the majority of conflicting evidence, including the BMA's own previous work. Several provably wrong figures were removed after initial publication, but the review is still viewed as distorted, excluding not only references included in the 1999 BMA study, but the 1999 study itself. Debate continues within the BMA.

The World Health Organization is currently awaiting the results of a Cochrane review of bicycle helmet legislation before forming a view on whether to support compulsion.

Overall, according to CTC, the UK's national cyclists organisation, "the evidence currently available is complex and full of contradictions, providing at least as much support for those who are sceptical as for those who swear by them."

Reduction in bicycle participation
Mandatory bicycle helmet laws have been linked to a reduction in the number of cyclists. For example, when mandatory bicycle helmet laws were enacted in Australia, slightly more than one third of bare-headed cyclists ceased to ride their bicycles frequently. The reduction in the number of cyclists is likely to have a greater negative impact on the health of a population, than would have resulted from any increase in injury. The long term health benefits of bicycle use are manifold and extensively documented, and so any reduction in bicycle activity will likely have a negative impact on the overall health of a population.

As well as being an extra expense, cycle helmets make cycling less convenient; they are bulky and often cannot be stored securely with bikes. They are incompatible with some hairstyles, forcing bicycle users to recreate their hairstyle after each journey.

Cycle helmet promotion or high levels of use may deter cycling by reinforcing the misconception that bicycling is more dangerous than traveling by passenger car.

Finally, others have argued that the wearing of bicycle "crash-helmets" has subjected children to ridicule. For example, in the 2006 film The Benchwarmers, the character Clark — played by Jon Heder — sports a bicycle crash helmet as an accessory prop to highlight his lack of social skills and physical coordination. If children are dissuaded from learning to cycle because of this, they will be considerably less likely to ride as adults.

All of these factors can lead to an increased risk for those cyclists remaining on the road, due to a "safety in numbers" effect. According to one study, the probability of an individual cyclist being struck by a motorist declines with the 0.6 power of the number of cyclists on the road. This means that if the number of cyclists on the road doubles, then the average individual cyclist can ride for an additional 50% of the time without increasing his probability of being struck. It is thought that the increased frequency of motorist-cyclist interaction creates more aware motorists.

Helmets and risk of injury
Many believe that a helmet can save a cyclist's life, an idea which is repeatedly asserted in debate. There is no known evidential basis for this claim and there are no known cases where mass helmet use has actually reduced the number of cyclists' deaths or serious head injuries. Association with increased risk of death has been reported. It is likely that helmets could prevent a significant number of minor cycling injuries but the overall safety benefits are inconclusive; this is thought to be in part due to risk compensation behaviour. A cost-benefit analysis of the New Zealand helmet law showed that the cost of helmets outweighed the savings in injuries even taking the most optimistic estimate of injuries prevented.

While a helmet may mitigate the effects of a fall or collision, other factors (such as maintenance, road conditions, and driver behaviour) are more important for reducing the chance of such accidents in the first place. In general, the value of bicycle helmets has been systematically overstated.

Some studies have even suggested that helmets increase risk. Although the head injury rate in the US rose by 40% as helmet use rose from 18% to 50%, this does not necessarily mean that helmets themselves increase risk. In fact, a range of theories exist to explain the observed disparity, including:
 * Risk compensation: helmeted cyclists may ride less carefully; this is well supported by evidence for other road safety interventions such as seat belts and antilock brakes.
 * Recent evidence from Walker (Accident Analysis and Prevention) suggests vehicles pass helmeted cyclists with measurably less clearance (8.5 cm/3.5") than that given to unhelmeted cyclists (out of an average total passing distance of 1.2 to 1.3 metres), indicating additional risk compensation by motorists too.
 * Poor fitting
 * Increased automotive road traffic

Promotion and compulsion
Helmet use has increased significantly in many, but not most, jurisdictions since the 1980s, primarily because of helmet promotion and compulsion laws. The following countries have mandatory helmet laws, in at least one jurisdiction, for either minors only, or for all riders: Australia, Canada, Finland, Iceland, USA, and New Zealand. In the U.S. 21 states have mandatory helmet laws. An analysis of helmet laws in the British Medical Journal showed that these laws have failed to yield measurable reductions in head injuries. The major documented effect of helmet laws is to reduce cycle use.

Use of cycling helmets is supported by numerous groups including the United States American Medical Association and the American National Safety Council. According to the NSC, head injuries cause 85 percent of bicycling fatalities, although it is unclear whether this is markedly different than for all trauma fatalities.

It is plausible that if a rider chooses to use a helmet, and maintains their safe cycling habits, they should be moderately safer than if they chose not to wear a helmet, although risk compensation theory states that an intervention as obtrusive as a helmet will very likely affect riding practice at the subconscious level.

Promotion of helmets is somewhat more problematic. Helmet promoters routinely make claims which manufacturers cannot, due to truth in advertising restrictions. Promotion campaigns are often supported and/or funded by manufacturers. Bell, one major helmet manufacturer, supports both helmet promotion and, through its Legislative Assistance Programme, laws. The major problem with helmet promotion, from the point of view of cycle activists, is that in order to present the idea of a "problem" to match the solution they present promoters tend to overstate the dangers of cycling. Cycling is, according to the evidence, no more dangerous than being a pedestrian. In fact, helmet compulsion in cars would be far more effective at reducing injuries than on bicycles.

Some bicycle activists complain that focus on helmets diverts attention from other issues which are much more important for improving bicycle safety, such as training, roadcraft, and bicycle maintenance. Of 28 publicly funded cycle safety interventions listed in a report in 2002, 24 were helmet promotions. For context, one evaluation of the relative merits of different cycle safety interventions estimated that 27% of cyclist casualties could be prevented by various measures, of which just 1% could be achieved through a combination of bicycle engineering and helmet use.

Data from around the world shows that despite the optimistic claims for injury reduction made by their proponents, no helmet law currently in force has led to a measurable reduction in cyclist head injury rates. There are a number of plausible explanations for this:
 * the studies on which the laws are founded mainly compare those who choose to wear helmets with those who do not; forcing a cyclist to wear a helmet will not make them behave like the kind of cyclist who wears one by choice
 * helmets are not designed to withstand motor vehicle impacts, but these account for most serious and almost all fatal cyclist injuries
 * governments do not tend to measure minor injury rates any protective device would be expected to be much more effective against minor injuries, rapidly tailing off with severity – although a few studies do claim that cycle helmets are more effective against serious than against minor injuries, it is more likely that the efficacy figures cited in advance are against a type of injury which subsequent statistics will not measure
 * while not a universally observed phenomenon, helmet laws tend to deter cycling; the theory of safety in numbers asserts that cycling becomes safer the more people who do it.

Cycling as a dangerous activity
Ordinary cycling is not demonstrably more dangerous than walking or driving, yet no country promotes helmets for either of these modes (although there was an experiment in Japan with walking helmets for children, which demonstrated no measurable benefit). Cycle helmet use correlates inversely with the level of cycling in a given country.

Detailed analysis of hospital admissions data also fails to support the idea that cycling is unusually dangerous: a study in the UK found that the proportion of cyclist injuries which are head injuries is essentially the same as the proportion for pedestrians at 30.0% vs. 30.1%.

Overall, cycling is beneficial to health – the benefits outweigh the risks by up to 20:1. Critics assert that anything which jeopardises that benefit should be carefully weighed to ensure it is likely to achieve some meaningful benefit in turn. Thus far, no helmet law has been shown to do that.

Case studies/risk

 * Thompson, R., Rivara, F. and Thompson, D. (1989), A Case-Control Study of the Effectiveness of Bicycle Safety Helmets, New England Journal of Medicine, 25 May, 320:21, 1361–67 Abstract &mdash; (The most widely cited pro-helmet study.)
 * Bicycle Helmet Research Foundation, "Commentary on A Case-Control Study of the Effectiveness of Bicycle Safety Helmets", accessed 21st June 2006
 * Scuffham Trends in cycle injury in New Zealand under voluntary helmet use, Langley. Accident Analysis and Prevention, Vol 29:1, 1997 &mdash; (Showed no benefit from large-scale increases in helmet use.)
 * John Adams, 1995, Risk, Routledge, ISBN 1-85728-068-7 &mdash; (Authoritative reference on risk compensation theory.)

Helmet Fit

 * Parkinson, Gregory and  Hike, Kelly E. (2003), Bicycle Helmet Assessment During Well Visits Reveals Severe Shortcomings in Condition and Fit,     Pediatrics, 2 August 2003   Vol. 112 No. 2, pp. 320–323 &mdash;  (Showed that correct fitting is an exception.)

Reduction of fatalities or serious injuries

 * Thompson DC, Rivara FP, Thompson R., "Helmets for preventing head and facial injuries in bicyclists", The Cochrane Database of Systematic Reviews 1999, Issue 4. Art. No.: CD001855. DOI: 10.1002/14651858.CD001855
 * Keatinge, "Objective observation of helmet use is essential"
 * Farris, Spaite, Criss, Valenzuela, Meislin, "Observational evaluation of compliance with traffic regulations among helmeted and nonhelmeted bicyclists", Ann Emerg Med 1997 May;29(5):625–9

Compulsion Laws

 * BikeBiz (industry journal), "Helmet battle flares up in BMJ", March 24, 2006
 * BikeBiz (industry journal), "Let's fight for our rights to the road, argues CTC", Feb 27th 2006
 * British Medical Association, "Legislation for the compulsory wearing of cycle helmets", November 2004
 * D Hendrie, M Legge, D Rosman, C Kirov, "An economic evaluation of the mandatory bicycle helmet legislation in Western Australia", Road Accident Prevention Research Unit, Department of Public Health, The University of Western Australia.
 * Hagel, Macpherson, Rivara, Pless, "Arguments against helmet legislation are flawed" Br med J, 2006;332:725–726 (25 March), doi:10.1136/bmj.332.7543.725
 * Merton, R.K., "The Unanticipated Consequences of Purposive Social Action", American Sociological Review, Vol.1, No.6, (December 1936), pp.894–904. (see Unintended consequence)
 * Scuffham, Alsop, Cryer, Langley, "Head Injuries to Cyclists and the New Zealand Cycle Helmet Law", Accident Analysis and Prevention, 2000, 32: 565–573
 * Vulcan, A.P., Cameron, M.H. & Heiman, L., "Evaluation of mandatory bicycle helmet use in Victoria, Australia", 36th Annual Conference Proceedings, Association for the Advancement of Automotive Medicine, Oct 5–7, 1992.
 * Vulcan, A.P., Cameron, M.H. & Watson, W.L., "Mandatory Bicycle Helmet Use: Experience in Victoria, Australia", World Journal of Surgery, Vol.16, No.3, (May/June 1992), pp.389–397.

Bicycling as traffic books

 * John Forester, 1992, "Effective Cycling", ISBN 0-262-56070-4
 * John Franklin, 1999, "Cyclecraft", ISBN 0-11-702051-6