As I write the traffic is still backed up from the Wandsworth Road – I can hear an occasional frustrated honk from a trapped van man, or the stifled yawp of an emergency services vehicle threading its way through the metallic mesh. I’ve only been out this morning to walk the dog: a turd-bagging totter around the block but even here, several hundred yards away from the actual road closure, there are sheepishly bemused drivers diverted away from the flock.

Yesterday morning I was sitting on the top deck of the 88 bus: the traffic was slower than usual heading down the South Lambeth Road and as we reached Vauxhall Cross there began to be the unmistakable signs of an accident having just happened: fire engines shouldering cars over to the kerb and even firemen, on foot, running. By the time we were chugging over Vauxhall Bridge I’d overheard a man a few seats ahead of us say that a helicopter had crashed into the crane on top of the new cylindrical tower that, for the past few months, has been being extruded from the embankment – another architectural abomination to sully the London skyline.

Before we’d gained the north bank of the Thames, and despite the fog, my wife – who was sitting beside me – had visual confirmation: she could see the broken jib of the crane. It was about 8.15am and the crash had happened only a few minutes before. Back at home a couple of hours later I had a phone call from the man who mends my typewriters – he lives in a suburb of northwest London and had seen the crash reported on the news. Was I, he wanted know, all right? My wife was a little dismissive of his solicitude, seeing it as a slightly wacky example of ambulance-chasing by proxy, but with my fine attunement to – and sympathy with – the madness of crowds, I was rather touched by his concern.

True, this was the first time that anyone in London had ever been killed by a helicopter falling out of the sky on top of them but the singularity of the event only made it more paradigmatic. In survey after survey, people report that the greatest dangers they face are, in this order: terrorist attack, plane crashes and nuclear accidents. This despite the fact that these three combined have killed fewer people in the past half-century than car accidents do in any given year.

True, the mediatisation of certain kinds of spectacular events – the attack on the Twin Towers being the most obvious example – ensures they remain high in the anxiety hit parade, but I think there’s more to it than that. Human agency also makes us antsier: the idea that an individual or group of individuals is out there acting with malevolent intent is, we feel intuitively, a threat we should be able to assess and act upon – whereas there can be no anticipation of acts of God (or gods), unless, that is, we have a shamanic capacity for prognostication. It perhaps seems unfair but even human error of the kind that was probably involved in the helicopter crash, is, I would argue, grouped by our psyches under the heading of the potentially avoidable.

It may be crazy but in a deep recess of the group mind we imagine that we ought to reason along these lines: hmm, looks foggy out this morning, I think I’ll give Wandsworth Road a swerve – they’ll have switched off the warning lights on top of that crane and an unwitting helicopter pilot might crash into it . . . That this is a vanishingly small likelihood is neither here nor there, because the perceptual equipment required to swim safely through the urban mill race includes the expectation of other humans’ cock-ups as standard – along with airbags and safety belts.

All of this also helps explain why it is that public-safety campaigns need to be quite so relentless: they’re in competition. The wildcard helicopter crash gets free blanket coverage, but the 4,000 annual car fatalities have to pay for their bus shelter space. And with spectacular events taking up so much of the available anxiety quotient, we need to be constantly reminded of the more workaday threats to our mortality – threats that, while they may also be functions of human error, have become so ubiquitous that we’ve begun to apprehend them as natural phenomena. The traffic – like a river – either flows, or it is damned; and when it’s damned it backs up: a great logjam of frustration, anger and anxiety from out of which will come a host of misfortune. I’m not going to risk fording it – I think I’ll stop at home for the rest of the day.