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Since You Asked

I'm amazed at how easy it is to drive the new south Medford interchange, and am driving it every day. But there's one thing I wonder every time I go over it — why is the contraption with the traffic signals on it so ginormously huge? It's not your usual traffic signal pole, by any stretch of the imagination.

— Ann L., Talent

That's no ordinary interchange, Ann, so it's only fitting that it should have an extraordinary structure for the traffic signals.

We took your question to Gary Leaming, the man with the answers for the Oregon Department of Trans-portation. He talked with highway engineers and got the details.

The signal structure is a steel tube made up of multiple components. It's just a shade more than 168 feet long and weighs 30 tons. It cost about $289,000.

The length of the tubular span dictates the size of the steel tubes, which are about 4 feet in diameter.

Leaming said engineers designed the span, and its large base, to reduce vibration that might occur in windy conditions.

As an added, unexpected benefit, the signals are configured so that drivers shouldn't be blinded when the sun is low on the horizon in the morning and evening.

Leaming said a truss system was considered for the signals, but the open span that was needed for this site made it unsuitable for the ordinary highway design standards, so the engineers went with what you see.

There may be another safety benefit, too. Drivers sometimes find that they "lose" traffic signals in those large truss systems that support signs and signals. That shouldn't happen at the south interchange.

Send questions to "Since You Asked," Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; by fax to 541-776-4376; or by e-mail to youasked@mailtribune.com. We're sorry, but the volume of questions received prevents us from answering all of them.