Helmets v cameras

It has been pointed out more than once that there is a potential similarity between the campaign against helmet compulsion and that against speed cameras. Honesty compels me to acknowledge that there are indeed parallels - but there are also, I believe, profound differences. Let us consider the two issues side by side, and see whether the speedophiles have more in common with helmet sceptics than might be supposed.

Similarities
I'll start with the common ground. Having spent longer than I care to recall debating the issue of speeding and speed cameras, I think the two issues have the following in common:


 * Challenging Orthodox Views. The first and most obvious similarity is that both helmet sceptics and camera opponents are challenging a dominant orthodoxy in road safety thinking.
 * Risk Compensation. Both speed cameras and cycle helmets are attempts to limit risk without controlling the propensity to take risk - what Adams describes as "bottom-loop biased", after the bottom half of his "risk thermostat". In both cases there is an attempt to coerce those affected into accepting lower levels of risk than they like, rather than modifying their risk preference or reappraising their (possibly faulty) perception of risk.
 * A Question Of Scale. Much of the most widely cited evidence for both cameras and helmets comes from small-scale studies, often conducted by those who have already made up their minds or have a vested interest in the outcome, whether it is traffic engineers supporting traffic engineering solutions to the fundamentally sociological problem of risk-taking drivers, or the Snell Foundation financially supporting studies which show benefit from helmet use, .  And in both cases these groups will be strongly resistant to any evidence which challenges them: whether it is traffic engineers disputing the existence of regression to the mean or Thompson, Rivara and Thompson absolutely denying the possibility of risk compensation, to admit the counter-evidence would be to weaken the source of much of their funding.  Both exhibit the classic signs of policy-based evidence making.
 * Selfishness. Both groups want to see the utility of their chosen mode boosted, and both see the other side as impeding that.
 * Activists and Enthusiasts. Both groups are dominated by activists who are enthusiasts for their chosen mode of transport.

Differences
Those are the similarities, then, but what of the differences?

Dangerous To Whom?
There is no possible doubt that speeding motorists pose a danger to others than themselves. Unhelmeted cyclists, by contrast, are unlikely to pose danger to others as a result of their choice of headgear (although the same may not be true of helmeted cyclists - but to an unknown and quite possibly unmeasurable extent). Some drivers deny that speeding motorists pose danger; they fall back on the argument that 31mph is scarcely more dangerous than 29mph. This is a fallacious argument (the "fallacy of the heap"). The kinetic energy of collision rises with the square of speed, and the probability of fatality in a collision rises with anything up to the fourth power of speed. No credible argument has yet been advanced to the contrary.

Research Evidence
Helmet sceptics can and do quote significant volumes of research evidence to support their arguments, some of it in the form of critiques of pro-helmet work but much of it independent work by statisticians and risk management experts.

The anti-camera lobby by contrast makes much use of proof by assertion and loaded terms such as "inappropriately" low limits. It is possible that this perception is skewed by the actions of a single individual, whose tendency is to describe all research showing that speed increases collision or rates or injury severity as "flawed", "discredited", "despicable" or any one of a basket of similar epithets. The fact remains that there is little or no peer-reviewed data to contradict the idea that severity and probability of collisions both rise with speed for a given class of road.

Conflation of Arguments
This is both a similarity and a difference, but more of a difference. Anti-camera activists will oppose cameras using arguments against speed limits, but when confronted with overwhelming public approval of speed limits as a concept will argue that speed limits are themselves only a problem when they are enforced, a reversal of the argument. This is closer to the pro-helmet lobby's position on compulsion, where the "obvious" desirability of helmet wearing is used as justification for laws, rather than advancing sound justification for compulsion where the supposed risk applies largely to one voluntarily taking on that risk.