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Safety zone exceeds 10 miles from lightning

Question: We've been experiencing a lot of "heat lightning" lately. When it occurs, should we take any precautions?

Answer: Heat lightning is lightning that appears as a glowing flash in the distance, sometimes even near the horizon, without thunder being heard, said Greg Forbes of The Weather Channel. This is usually lightning in the upper portion of a distant thunderstorm whose base actually may be below the horizon.

Thunder usually can't be heard at locations much more than 15 miles away from the lightning strike. For this reason, Forbes said, distant lightning seen without thunder being heard usually isn't a safety threat. About the farthest

that a "renegade" bolt has struck outside the main lightning area of a thunderstorm is 10 miles.

The usual safety rule is to take precautions when the time lapse between lightning and thunder is 30 seconds or less, which amounts to a distance of 6 miles (thunder travels about 1 mile in 5 seconds), Forbes added. On rare occasions, lightning can strike 10 miles away from previous strike positions in the storm, so a more cautious time lapse for taking shelter would be 50 seconds.

Busy highways

Question: An article stated that I-80 may be the nation's busiest highway. Is this true?

Answer: The U.S. Department of Transportation couldn't confirm that I-80 holds that title. One DOT researcher reported that I-95, from Maine to Miami, is the busiest, but provided no statistical information to support it.

The Federal Highway Administration does, however, compile quarterly statistics on "principal arterials" (segments of highways) that carry 200,000 or more vehicles per day.

As of January 2002, the most recent data available, the highest traffic count reported was along a 12-lane segment of I-5 in California's Orange County: 365,852 vehicles a day. A 5.35-mile segment of I-80 between Oakland and San Francisco averaged 269,472 vehicles a day.

On noninterstate segments, the highest count was 320,283 vehicles a day on a 10-lane section of U.S. 101 in Los Angeles County.

Have a question about the news? Colin Bessonette will try to get an answer. Call (404) 222-2002 or write to him at the Atlanta Journal-Constitution, P.O. Box 4689, Atlanta, GA 30302, or e-mail him at q&aajc.com.

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