«

»

Nov
17
2007

Risk compensation deniers

In October 2007 the Insurance Institute for Highway Safety published a Status Report (PDF: 1MB) complaining about my article “Britain’s Seat Belt Law should be Repealed” (PDF: 0.2MB) (published as “Seat Belt Laws – Repeal them?” in the June 2007 issue of the statistical journal Significance). It went on to denounce all those who invoke the risk compensation effect to question the efficacy of seat belt laws. It concludes: “Don’t believe them, not until they produce credible evidence that people compensate for safety”.

I first produced evidence on the subject sufficiently credible to pass peer review for publication in the Society of Automotive Engineers Transactions in 1982 – “The Efficacy of Seat Belt Legislation” (PDF: 0.2MB). I have revisited the evidence that people monitor their environments for signs of safety or danger, and adjust their behaviour in response to perceived changes, in numerous publications since, including two books: Risk and Freedom: the record of road safety regulation (1985) and Risk (1995).

The idea that people compensate for safety was considered outrageous in 1982,  and still is by the Insurance Institute for Highway Safety: “To believe Adams you’d have to believe that people have a certain tolerance for risk and that their levels of risk are regulated by a homeostatic mechanism so that, if forced to “consume” more safety than they voluntarily would choose, people will balance the safety increase by taking more risk. It’s a stretch, isn’t it?” 

The “stretch” appears to be now becoming conventional wisdom. It underpins the increasingly popular concept of shared space (PDF: 15KB); Hans Monderman, the Dutch originator of the concept spoke to an enthusiastic sold-out meeting in London’s City Hall this week. And it is even finding its way into government planning guidance in Britain. This quotation can be found in the Department for Transport’s Manual for Streets: evidence and research (PDF: 10MB): “One of the most important variables that needs to be taken into consideration is ‘risk homeostasis’ – the way in which drivers adjust their behaviour to maintain a consistent level of risk. As drivers feel safer they begin to take more risks, whereas conversely, if road conditions make them feel unsafe, drivers are likely to adjust their behaviour to take fewer risks.”

2 comments

No ping yet

  1. Guy Chapman says:

    This is a classic example of reasoning back from a conclusion. IIHS nailed its colours to the mast of seat belts many years ago, to the point that it has become an article of faith with them. It is one of their examples justifying their own existence, that such measures are now in place.

    Anything that challenges their shibboleth must, therefore, be wholly and fundamentally wrong. Ask a member of IIHS if they would drive without a seat belt, and if not, why not. I bet you a pound their answer will be a practical indication that they risk compensate.

    It is absurd to suggest that people do not compensate for levels of perceived risk. The only question is by how much. You can have a rational discussion around the balance of levels of perceived risk, degrees of compensation, and whether the actual benefit would outweigh the resultant change in behaviour, but to deny the existence of risk compensation simply because you dislike a proposal that uses this mechanism as a supporting pillar is fatuous and indicates a profound lack of intellectual rigour.

  2. Jim Tubman says:

    The “Status Report” article appears to be a slightly shortened version of the text found in the “IIHS Advisory” No. 33, April 2007 (easily found by a web search). The latter article includes seven references to studies that conclude that drivers do not take more risks when they are required to use safety belts; these references were not in the “Status Report” piece.

    I haven’t read the papers and therefore cannot comment on the quality of their data or reasoning, but it would be fair to say that IIHS believes there is more to their opposition to risk compensation than simply finding the idea distasteful. They have some research they can point to.

    That said, both IIHS articles do not mention the failure of Britain’s seat belt law to provide anything close to the projected reductions in deaths and injuries, let alone provide some alternative explanation of that outcome. Their silence on this matter would suggest that on the issue of risk compensation, the IIHS position is not so solid, and Prof. Adams’ position is not so weak, as the IIHS would have their readers believe.

Leave a Reply

Your email address will not be published.

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>