B31 or B-31 may refer to:
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B-31 (Michigan county highway)
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B31 (New York City bus)
The Metropolitan Transportation Authority (MTA) operates a number of bus routes in Brooklyn, New York, United States; one minor route is privately operated under a city franchise. Many of them are the direct descendants of streetcar lines (see l ...
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Bundesstraße 31
The Bundesstraße 31 (B 31) is a federal highway or ''Bundesstraße'' running from east to west in South Germany. It runs from Breisach on the border with France to the Sigmarszell junction on the Bundesautobahn 96 (A 96) near Lindau. B ...
, a German road
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Douglas XB-31
The Douglas XB-31 (Douglas Model 332) was the design submitted by Douglas after the request by the United States Army Air Forces for a very heavy bomber aircraft, the same request that led to the Boeing B-29 Superfortress, Lockheed XB-30, and Co ...
, an experimental aircraft
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