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In response to our recent post about traffic accidents in Wallingford, Marc wrote in that, according to the book “Traffic“, more pedestrian injuries occur at traffic lights than from jay-walkers. We thought it an interesting digression for fiercely anti-jay-walking Seattle and did some poking.

First, we fear statistic commits the most frequent and misleading crime that popular press writers commit, omitting the base rate. In other words, it doesn’t take into account the relative sizes of the populations from which the numbers are drawn. Imagine this hypothetical reality:

• 1,000,000 people cross the street
• 95% of people cross at the stoplight, 5% at jaywalk mid-street
• 5% of people crossing at a stoplight have an accident
• 50% of jaywalkers have an accident

If these hypothetical numbers were true, you would find that almost 50,000 accidents occured at the stoplights compared to half as many at mid-street, but crossing at mid-street would still be 10x as dangerous as crossing at the stoplight.

You see this type of confusion in statistics all the time. For example, if a toxin raises your chances of contracting a disease by 10x, but your chances of getting the disease was only .001% to begin with, it’s not nearly as bad as another toxin that only doubles your chance of getting a disease if your initial chances of getting that disease were 1%.

OK, statistics class dismissed. Let’s head out for recess, provided by the New York Times’s Traffic book review:

An alternate title for the book might be “Idiots.” Vanderbilt…cites a finding that 12.7% of the traffic slowdown after a crash has nothing to do with wreckage blocking lanes; it’s caused by gawkers. Rubberneckers attend to the spectacle so avidly that they themselves then get into accidents, slamming into the car in front of them when it brakes to get a better look or dig out a cellphone to take a picture. (This happens often enough for traffic types to have coined a word for it: “digi-necking.”) Exasperated highway professionals have actually tried erecting anti-rubbernecking screens around the scenes of accidents, but the vehicle toting the screen typically gets caught in the traffic jam it’s meant to prevent.

Moreover, Vanderbilt adds, “there is the interest in the screen itself.” Drivers will slow down to look at anything: “Something as simple as a couch dumped in a roadside ditch can send minor shudders of curiosity through the traffic flow.”