Science on the sidewalk: a brief tour

Now there's something you see every day - a stoplight! But look closely. Can you spot something odd about the light? What's with all those dots? Is the lens of the light doing that? Or is it something else? (Answer: It's something else.) Look around as you go to school, cross the street, go shopping. Ask questions. You may start to notice extraordinary things about ordinary objects (is that a credit-card slot on that parking meter?), or become curious about the inner workings of things you see all the time (if you push the "walk" button lots of times will the light change faster?). Here are a few extraordinary stories of everyday things to get you started.


We regret to say that it was a newspaper editor who came up with the idea for the parking meter. Carlton Cole Magee was appointed to a traffic-control commission in Oklahoma City in the 1930s. The device he envisioned would keep drivers from hogging the best spaces in front of stores. Making money for the city was secondary.

The first 24 Park-O-Meters appeared in downtown Oklahoma City on July 16, 1935. The clockwork meters - it cost a nickel to park for an hour - were manufactured by the Dual Parking Meter Co., founded by Mr. Magee.

Today the United States has more than 5 million parking meters in operation. Think of it: If every meter collects at least 25 cents a day, they will amass about $325 million a year, notes Ron Luttrell, a parking-meter historian in Oklahoma.

Tomorrow's meters will be more convenient to use, and smarter, too. Many meters already are battery powered, with digital displays. They also have foreign-coin detectors: If you try to use a non-US coin or an arcade token, a little red light starts to flash to alert parking-meter attendants.

Boston's 10-person meter crew still finds 400 pounds of non-US coins in the city's 7,000 meters every year.

What do they do with them all?

"The coins and slugs are sitting in a warehouse in big buckets." says Chuck Morelli, director of transportation in Boston. "The banks won't process large amounts of foreign coins, and tokens are worthless. Any ideas?"

An experimental meter being tested in Boston and a few other cities lets drivers use a special credit card. The amount of time you select is automatically deducted from the card's magnetic strip. The cards can be "recharged" with money. And the special meters still accept coins.

New York City is also testing a more advanced model. This one has an infrared electronic eye that can tell when a car arrives - and when it leaves. And when a car leaves, the meter resets itself to zero.

"No more free parking on time that someone else has paid for," Morelli says.

Which brings us to parking tickets. The first parking ticket was issued to the Rev. C.H. North of Oklahoma City soon after the meters were installed that July day in 1935. The story has a happy ending, though: The ticket was dismissed when North explained that he had gone into a store to get change.


Have you noticed that some traffic lights - particularly red lights - are a lot brighter than they used to be? And would you believe that these superbright traffic lights don't use light bulbs?

It's true. The new stoplights are really groupings of hundreds of LEDs (light-emitting diodes). LEDs are thin, solid-chemical compounds that glow when electricity passes through them.

LED technology is revolutionizing the traffic-light industry: LEDs don't burn out as fast as regular light bulbs. They cost more to begin with but are cheaper in the long run because they use far less electricity. They're safer, too, because people can see them more easily. (You may have also noticed LEDs being used for the third brake light on most cars built after 1993.)

The changeover from bulbs to LEDs started about three years ago. Red, green, and yellow LEDs are available, but most cities have opted to replace only the red lights with LEDs. Red LEDs cost the least.

"Yellow is usually never replaced because these lights are not on long enough to really notice a savings in electricity," says Northe Osbrink, LED specialist for Hewlett-Packard. "Yellow lights are only on 12 percent of the time, while reds are on 66 percent of the time."

As for green, it's the most expensive LED to produce. Most cities are waiting until the price goes down to install them. (Did you know that a non-LED green light isn't really green? It's blue-green. That's for people who have trouble distinguishing between the colors red and green.)

LEDs run on 7 to 18 volts of electricity. The old light bulbs need 70 to 108 volts. LEDs last as long as 15 years, while conventional bulbs must be replaced (so they don't burn out) about twice a year.

LED traffic lights are vastly different from the first illuminated traffic signal. The first traffic light stood atop a 22-foot-high iron pillar at the corner of Bridge Street and New Place Yard off Parliament Square, London, in 1868.

Invented by J.P. Knight, the light was a revolving lantern illuminated by natural gas, with red and green signals. Red meant "stop," but green didn't mean "go." Green signaled "caution."

The light was turned by hand using a lever at the base of the pole. A gas-powered traffic light wasn't the best idea, though, as they found out one day when the light exploded.

In 1914, Cleveland became the first city in the US with an electrically powered traffic signal. It had red and green lights, plus a warning buzzer that sounded just before the light changed.


You're standing at a crosswalk. There's a scrumptious pizza joint across the street. And your stomach is growling like a bear. You must get across.

You push the button that stops traffic and illuminates the "walk" sign. You press it again. Again. Four times. Nothing happens. Is it broken?

"Press the button as many times as you want," Boston's Morelli says. "It doesn't do any good to press a lot of times. It just takes one firm press."

Crosswalk lights run on a cycle. When the button is pressed, it signals the mechanism that pedestrians want to cross. So the next time it reaches the end of the traffic-light cycle (but not before), it will light the "walk" signal.

City transportation departments determine how long pedestrians must wait. At intersections with lots of traffic but few pedestrians, the crosswalk may be programmed to light every two or three cycles. If pedestrian traffic is heavy, the crosswalk may light after each cycle, and stay on longer.

Don't worry if the "don't walk" signal starts to flash after you've started across the street. Traffic planners know how long it will take to cross a particular street. They have programmed the crosswalk timers accordingly. "All the flashing 'don't walk' signal means," Morelli says, "is that if you haven't stepped off the curb, don't cross the street." If you walk at about four feet per second, you'll have plenty of time.

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