Big Brother in the Odometer
How does the government know how much I'm driving? Americans have reduced the number of miles they drive each month since November, according to a report released Wednesday from the Federal Highway Administration. Americans drove 53.2 billion miles fewer than they did over the same eight-month period a year ago. How does the U.S. government know how much time I'm spending in my car? Four thousand little sensors and a bit of algebra. States install traffic sensors on urban and rural roads and interstate highways to count cars and, sometimes, to determine their size. (You may have noticed their lane-wide rectangular outlines embedded in the pavement.) Some sensors detect vehicles by their weight. Others detect a car's metal underbelly with an electromagnetic field. At the end of every month, the states pass the car-counting data to the feds, who plug them into a formula to estimate how many miles Americans drive each month. A pair of sensors placed near each other can sometim...