Ham Barn Roundabout is a roundabout on the A3 in Hampshire. It is named after Ham Barn farm to the north of the roundabout.
It is now the only non-grade separated junction on the A3, outside of London or the Portsmouth urban area. The layout was chosen because the Liphook Bypass, between here and Hindhead, was expected to be built as a single carriageway and design standards recommend that the transition from dual to single carriageway is made via a roundabout. However, late in the day the decision was made to build the new road as a dual carriageway, but the junction layout wasn't changed.
A full upgrade to the junction seems unlikely, but signalisation has been proposed.