The Patiala State Monorail Tramway.
The Ewing System solved the problem by being not quite a monorail- most of the load went on the single ground-level rail, using double-flanged wheels, but some 4 or 5% of the weight was carried on a road wheel that stopped it tipping over. The small amount of load on the road presumably did not detract much from the low rolling resistance of the steel wheel-steel rail interface.
The road wheel would take exactly the same path each time, and on the unsurfaced roads of the day this must have tended to wear a groove; quite possibly the PSTM had a tendency to lean towards its road wheel. At least this would have been in the direction of increased stability. W J Ewing was a British inventor; he seems to have abandoned his attempts to patent the concept.
Left: The preserved Patiala monorail locomotive, in full steaming and working order at the Indian National Railway Museum in Delhi.
Picture by kind permission of Prakash Tendulkar.
More of his pictures of this monorail can be seen at: http://www.trainweb.org/railworld/Trip%202001/PSMT/