The great evolutionary biologist, George C Williams died this week. One of his many contributions was to explore the population genetics of sex ratios — the relative abundance of males and females in populations. Williams observed that in most of the animal species that reproduced sexually, there were an equal number of males and females. But in most species this is hugely wasteful. Consider a species like deer, where one stag keeps a harem of does: a single male can mate with many females. And so the majority of males are evolutionary dead ends; from the point of view of cold heartless biology, they are wasted. It would be far more efficient if the species produced many fewer males.
This curious observation turned out to contribute to a major development in evolutionary biology: Williams and his colleagues realised that in a population that had many more females than males, any heritable tendency — any strategy — that led one lineage to start producing more males would be at an advantage, because those males would have a very high probability of producing hundreds of offspring. The rest of the lineages would be at a disadvantage, investing in females which would only ever have a few offspring. The many-males strategy, inherited by the hundreds of offspring, would become more common in the population. But then the population would no longer have many more females than males, and the strategy would no longer have an advantage: for each male there is now a much higher risk that they will not reproduce at all. Now, any lineage which took the opposite strategy — to produce safe females — would be at an advantage. The many-males strategy destroys the very conditions that make it a good strategy. This idea was part of the mid-20th century revolution that explained evolution as a process of fluctuating gene frequencies in populations: selfish genes and their strategies, competing in the context of the individuals and environment around them. The revolution finished-off the idea that anything in nature was done “for the good of the species”; all that exists in nature is the best set of strategies for maximising short-term existence that selfish genes have yet stumbled upon.
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Shared space is supposed to work by creating an unusual situation, free from all the signs and barriers, markings and signals that attempt to keep the road safe (or, at least, to manage the danger). It is proposed that road users will perceive this strange foreign situation to be unusually risky, and so the Motorist will compensate for that perceived risk by slowing down, and the pedestrian will compensate for the risk by keeping on eye on their surroundings. It’s all in the risk compensation. In Portishead, for example, the council have switched off the traffic lights and covered them with bright orange plastic. The users of the roads of Portishead do not need to perceive that under normal circumstances these are the sort of roads that would need signals to keep them safe. They have the signals right there saying it, better than any sign ever could. Shared space works in Portishead because road users perceive the road to be unusually risky, and they perceive it to be unusually risky because they can see a set of signals that are conspicuously switched off.
On normal “safe” non-shared roads, road users already take absurd risks with their own and others’ lives. London is stuffed with builders driving trucks while talking on phones, and minicabbers who will happily kill a cyclist just to get to the back of the next queue for the lights a couple of seconds quicker. As the saying goes, if the car were invented today, it would be banned by modern health and safety — and that doesn’t reflect badly on modern health and safety. We should surely be perceiving this great risk and adjusting our behaviour to compensate. But we don’t. Because the road is mundane. These risks are just our boring every day commute, or the least fun part of a family day out; the bit that makes the builder late for his job and the kids scream “are we nearly there yet”.
What happens when the signals in Portishead are not simply wrapped in plastic, but ripped out altogether? What happens when Bristol, and Clevedon, and Weston-super-Mare all do the same thing? When no streets anywhere have traffic signals? Road users will not be expecting to see them, will not consider their absence unusual. A shared space will be just another street, like all the other streets. Why should a road user perceive it as being associated with any greater risk than any other street? Why should Portishead’s shared space then be anything other than our boring every day commute? Why should Weston’s shared space be anything other than the least fun part of a family day out*? Why should a road user then adjust their behaviour to compensate for a risky shared space any more than they currently do for our already staggeringly dangerous roads?
Shared space is a strategy and it is strategy that relies upon its own novelty and rarity to be effective. When every street is filled with signals, signs, markings and bariers, shared space is a strategy that has a high probability of paying off big time. But as shared space becomes more common; as more road users become familiar with, and comfortable with shared space, every shared space scheme becomes less effective, until shared space becomes so common and mundane that they all fail. Traffic planners and politicians will suddenly discover that the opposite strategy, to attempt to manage the traffic, is more effective and attractive; that in the new population of streets, it is the traditionally managed ones that are the safer strategy. And so the population cycle will continue, to the great joy of traffic-light manufacturers and aggregate companies.
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Evolution is a nasty, wasteful, amoral process, with no forethought. Evolution provides short term incremental improvements at the expense of long-term progress. A small short-term sacrifice or investment that could pay-out a giant jackpot will simply be invisible to evolution. It is not something we should imitate or interpret as a parable for how to lead our lives. Civilisations should be capable of planning, cooperating, and acting for the good of the society. We should be able to recognise that for a short-term sacrifice and investment, we can come up with a strategy that is far superior than any of the equally wasteful and unsustainable variants on the car-dependency strategy.
* Weston was a bad choice of example, wasn’t it?
At War With The Motorist 
Shared Space is only intended for very low traffic speeds (10mph or less) and low traffic volumes (ie no through routes – not rat runs). The experiments that have been undertaken in the UK are merely removing some of the visual clutter (which is probably no bad thing in itself) and removing the cattle pen barriers that are annoying for pedestrians and dangerous for cyclists. However, without reducing the speed limit and enforcing it by using physical traffic calming measures -changing tarmac to rough cobbles (nothing like shaking out your filings to make you slow down), introducing chicanes, narrowing, additional planting and trees etc, shared space is little more than a PR soundbite and has no substance.