Risks, Relative and Absolute

Some Resources for the would-be Risk-Avoider

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Of all the "excuses" that people offer for using cars for micro-trips across town -- journeys of less than 5 miles, and sometimes even less than 1 mile, round trip distance -- the most common among Americans is simply that they are afraid. Cycling, most Americans feel, is terribly dangerous; it is much safer to be inside a car than out on the road and "vulnerable" on a bike.

Numerous academic studies show that there is a large gap between the average person's guess about the magnitude of a given risk and its true threat. This would scarcely be surprising if we were dealing only with very exotic or unusual events. But the fact is that even with respect to routine risks that we all run (for example, heart attack, cancer, or traffic fatality) there is generally a huge discrepancy between the true magnitude of a risk and the layperson's perception of it. For instance, ... the average American reckons the odds of his or her dying in a car accident this year to be about 1 in 70,000; the real figure is closer to 1 in 7,000.

-- Larry Laudan, The Book of Risks

The total number of deaths per annum in the United States is around 2.5 million. Of those, 151,000, or about one in 15 died "before their time" -- that is, by violence or accident. As George Shaffner notes (see below) "If you are lucky enough to live to be eighty years old, then about 12 million people will die from homicide, suicide, and accident within your lifetime." Of those, if current trends continue, only 80,000 will be cyclists -- 0.6 percent.

Now, we think (courtesy of surveys by the League of American Bicyclists among others) that only about 6.5% of Americans actually cycle with any regularity. If cycling were exactly as dangerous as everything else that people do, then we'd expect the percentage of accidentally dead cyclists among accidentally dead Americans in general to be about the same as the percentage of cyclists in the general population. That would mean 6.5 percent -- but the actual percentage of dead cyclists is one tenth of that; so it seems that cycling is about ten times less likely to kill you than the aggregate of all other risky things that people do.

This may or may not be a meaningful number; but certainly the average person believes that cycling is much more dangerous than the aggregate of normal activities (all of which entail some degree of risk).

Back to Laudan. His is a popular rather than a scholarly work, and it offers many interesting and (if your mind works this way) entertaining statistics which enable us to compare degrees of risk from wildly varying sources:

Items around the house most likely to produce injuries requiring medical attention (in descending order of threat!)
How many of us realize that more people every year seek medical attention due to injuries incurred while using or handling domestic furniture, than from injuries incurred while riding bicycles? Over 600,000 Americans per year are injured by their furniture, which adds up to about a 1-in-450 chance of injury for each of us! Slightly fewer (540,000) Americans are injured while riding bicycles (1 in 500 risk for each of us). (Bear in mind that we decided to accept, above, that only 6.5% of Americans actually cycle with any regularity.)

600,000 people are homeless on any given night in the USA, or about 0.2 percent of the population, and just about everyone else is using furniture of some kind. So we can state with some confidence that almost 100 percent of Americans are exposed regularly to the risks of furniture, as opposed to 6.5 percent who are exposed to the risks of cycling. In other words, cycling is about 15.5 times more dangerous than using a chair or bed. But I think most Americans would consider a bicycle far more than 15 times as dangerous as a chair, a bed, or a Barcalounger!

We may be over-frightened of bicycles, but we also seem to be under-frightened of cars. For example, most people are quite worried about disease and violent crime. But are most people aware that motor vehicle crashes kill more Americans every year than diabetes, suicide, homicide, or AIDS? As Laudan wryly notes, "Since the introduction of the automobile, almost 3 million Americans -- equivalent to a city the size of Chicago -- have died in auto accidents. If you are under 45 and male, motor vehicles are more likely to kill you than cancer, heart disease, or any other malady."

It is interesting that Shaffner concludes that the biggest factor in untimely death is not our choice of transport options, but gender! "Without question, the best way to reduce the likelihood of untimely death is to be a woman. Even if you were not born a woman, then you may wish to consider behaving like one."

Here are some not-very-well-known statistics which caught Laudan's eye:

Your risk of being killed in some sort of motor vehicle accident this year: 1 in 5,800.

Your risk of dying this year as an occupant of a car: 1 in 11,000.

If you are 19 or under and a licensed driver, your risk of being in a fatal accident: 1 in 1,500.

Your risk of being killed in a car is about twice as great as your risk of being a homicide victim.

The added risk of fatalities when interstate rural speed limits went from 55 to 65 mph: 19%. Serious injuries increased by 40%.

Of Americans who work outside the home, 84% travel by private motor vehicle. Because the average person lives 9.2 miles from work, he travels 4,600 miles to and from work annually. So, over a 40-year working lifetime, he runs about a 1-in-500 chance of a fatal accident en route to work.

Almost one-third of urban motor vehicle-related deaths are pedestrians.

The odds that a randomly selected pedestrian will be killed by a car this year: 1 in 40,000.

People's fears about disease are also, very often, misplaced. Heart disease kills more people in the US than any other medical condition, with cancer running a close second. People are often more frightened, however, of the famous communicative diseases; these are your odds of dying this year from the following "fear-inspiring" conditions.

This sheds a little light on recent campaigns intended to panic the American public about their increasing weight :-) While being very fat has its undeniable disadvantages (including prejudice and public opprobrium), you're far less likely to die this year from being fat than from riding in a car!

Laudan claims that if you ride a bike an hour a week for 20 years, your lifetime risk of being struck and killed by a car is about 1 in 50. Sounds scary! But compare this:

Among regular runners and joggers, 70-80% are hurt sufficiently badly each year to curtail or eliminate their running programs. Most likely site of injury: the knees.

One year of jogging at least 2 hours a week poses a risk of dying of about 1 in 10,000.

The risk that a participant in a strenuous exercise program will die while exercising: 28 deaths per million hours of exercise. Such strenuous exercise for one hour a day for a year sets your risk of death by exercise close to 1 in 100.

In other words, according to Laudan, your risk of being struck and killed by a car during 20 years of trivial cycling is only twice your risk of dying during strenuous daily exercise during just one year.

The lifetime risk the average American runs of dying in a car accident is 1 in 45, or just slightly higher than the lifetime risk for the "wimpy" cyclist mentioned above.

Most of us tend to be comfortable with activities that carry annual risks of a more or less unpleasant nature smaller than 1 in 100,000 or 1 in 50,000. The slightly less risk-averse find that their habits and hobbies come with about a 1-in-10,000 chance of serious misfortune.
Here we should note that the risk of being killed in a car this year, for the average American, is about 1 in 11,000, or "acceptable to the slightly less risk-averse."

However, it is notably the extremely risk-averse (i.e. timid or cautious) person who fears cycling, but thinks riding in a car is very safe. Very few Americans today think of driving or riding in cars as at all dangerous. We are far more frightened of crimes of violence and of diseases like AIDS.

Here's one more data point for scale. A risk of one in 100,000 is about the risk the average 65-year-old American woman runs of dying within the next hour. If you can imagine a risk ten times less than that, that's one in a million. A risk ten times more than that is about 1 in 10,000, or the level that Laudan feels most of us can handle without anxiety.

To put risks (population based) in perspective, Laudan collects the annual risk to the average American of various negative outcomes:

But, but, but! I hear you cry. That can't be right! Cars can't be more dangerous than AIDS. World wide, this is true. AIDS has killed over 19 million people in Africa; in 1999, 2.4 million Africans died of AIDS (of a total of 2.8 million victims worldwide). This dwarfs the death toll on America's roads. But within the US, AIDS is a lesser killer of the citizenry than their own cars.

Let's try multiplying up the number of American cyclists. If your risk this year (population based) of dying while cycling is one in 130,000 then if everyone cycled (16 times as many cyclists as today), that risk would be one in 8125 -- still far less than the general risk of all-causes death, or cancer in particular, and less than the risk of death by automobile (all roles) today.

Of course, if every American was a regular cyclist, there would be far fewer cars on the road at any given time, and the risk of death by automobile would be enormously reduced for everyone (drivers and non drivers alike).

Moreover, if every American was a regular cyclist (according to the CDC) our overall health and fitness would improve dramatically and fewer people would be dying of heart attack, adult-onset diabetes, and other diseases associated with affluence and a sedentary lifestyle.

It seems as though everyone would win -- everyone's risk would be reduced -- if we drove a lot less and cycled (and walked) a lot more.

de@daclarke.org
De Clarke