Speed Kills?

I grow increasingly irritated by road safety campaigns emphasising the dangers of excessive speed and the supposed benefits of enforcing arbitrary speed limits (http://www.20splentyforus.org.uk). Such slogans as 'it's 30 for a reason' (http://www.dft.gov.uk/think/) particularly annoy. It is not '30 for a reason'- to suggest otherwise is to treat a continuous variable ie, 'accident risk per unit velocity' as a series of discreet variables- implying that travelling below the speed limit is safe and above it is not. In reality, the speed limits imposed upon us are of course arbitrarily chosen by legislators based on value judgements attempting to balance (statistically derived) collision frequency against velocity, and there is no empirically sound reason to value their judgment over anyone else's.

Fatalities can never be entirely eliminated, since all events the occurrence of which are consistent with the laws of physics have a finite probability that is greater than zero. Conceivable, yet improbable events are inherently more numerous than probable ones- the number of possible outcomes tending towards infinity as their probability declines towards zero, (such that tackling each improbable possibility would require an infinite number of individual precautions).

Accepting this to be true, it follows that extra precautions can only reduce the fatality rates by some finite factor, and it is perhaps worthwhile to attempt to quantify an example:

Throughout 2006, the last year for which figures are available at the time of writing, the average Briton travelled 7133 miles- 4/5 of them by private motor vehicle (http://www.statistics.gov.uk/cci/nugget.asp?id=24). The average person spent 383 hours of this year travelling, equating to an average velocity of 18.6 mph. The total number of hours spent travelling by private motor vehicle per capita then might be approximated to 383 x 4/5 = 306.4 hours. Suppose we were to reduce our average travelling speed to 2/3 of its current value in the name of road safety (comparable to, for example, reducing the speed limit from 30 mph to 20 mph). In that case the total number of extra hours sacrificed to travelling per person, per year is given by: (383 x 3/2) - 383 = 383 x 1/2 = 191.5 hrs. There are approximately 60 million people in the UK, so the total number of man-hrs lost per annum is therefore 60,000,000 x 191.5 = 11,490,000,000, which equates to 1311643.8 years. The average Briton's life expectancy is ca. 80 years, so the total number of man-hrs lost to driving, as a consequence of such a reduction in speed would be equivalent to approximately 16,396 entire human life expectancies.

The current annual death toll from road traffic accidents is in the region of 3-4,000 per annum, of which presumably most have already expended at least part of their life-expectancies.

Against this, I am inclined to look on a speed limit reduction such as this as being equivalent to condemning some 16,000 new-borns every year to spending their entire life-spans, day and night, to constant driving. I suspect most people would consider that a fate worse than death.

Traffic Flows:

While stuck in another of Southampton's relentless traffic-jams recently, it occurred to me that the reasoning required to devise a traffic management system capable of avoiding major congestion problems is not greatly distinct from that required to keep a fluid flowing smoothly through a system of pipes. Thus I propose the following novel approach to designing road networks: The traffic is modelled as a homogeneous fluid, and, with the aid of a hydrodynamic engineer, the road network is modelled as a series of pipes, the cross-sectional areas of which are selected so as to maintain a uniform flow-rate through the system. The pipes are then taken to represent a series of roads, the number of lanes incorporated in each case being proportional to the cross-section of the pipes that represent them (rounded up to the nearest whole lane). The resultant road network should resemble a river water-shed- the smaller roads appearing as tributaries of steadily increasing size all feeding on and off of vast, multi-laned trunk roads. Given sufficient parking provision, the road system thus devised should largely eliminate the traffic congestion that now plagues this country- provided that the constant of proportionality between the notional pipe network's cross-sectional area and the number of lanes in the corresponding road network is sufficiently large.