relief road
From Longman Dictionary of Contemporary Englishrelief roadreˈlief road noun [countable] British English a road that vehicles use to avoid heavy traffic, usually built for this purpose an eastern relief road for city trafficExamples from the Corpusrelief road• The proposal for a Rhyl relief road could mean yet another where it crosses the A525.• The eastern district distributor road is part of the relief road system round the city of Leicester.