I'm a native speaker of UK English and this is what is used here - ie the Oxford ring road / London Orbital. Ring Road is more general and is more frequently used around medium sized cities and even smaller towns.

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Note added at 1 day11 hrs (2008-09-01 13:29:56 GMT)
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Indeed - UK as opposed to US :-)

However, I've just had a look for you... I was sure I'd heard colleagues in Indianapolis using "Ring Road", so just googled Indianapolis Ring Road, and found:

Indianapolis International Airport is adjacent to the I-465 ring road and is served by the Indy Go public bus, which drops passengers off directly outside the main entrance. Shared shuttle operations, hotel courtesy vans, taxis and limousines offer convenient alternative means to reach central Indianapolis, Greenwood and Lafatette. A taxi call button is available on the curbside if necessary.

Also, you know that in Lisbon there is a CRIL and a CREL - ie. Circular Regional Interior/Exterior de Lisboa... These are sort of a circular route, but really more of an arch around the city as they don't join to the south of the city. These would still be known as ring roads though.

Hope this helps. Sometimes it's difficult to see the wood for the trees in translation!!