Now, with the help of an artist support person, Mr Withnall, who is intellectually disabled, is turning his two loves into works of art.
He has limited motor skills and needs help to use a scroll saw to cut out wooden car shapes, and to paint vehicles designs on to the shapes.
But his support worker, artist Douglas Thomas, says Mr Withnall (26) is quite clear about what he wants to create.
"He comes up with the idea. It is usually a taxi, because he loves taxis. We find one in a magazine and trace it. I help him cut it, he put on the base coat and I guide him as he paints it.
"James has ridden taxis all over the world and they have been many different colours. But he is always happy with yellow and blue".
The pair have been working together for three years, at first making single vehicle shapes and the occasional aeroplane or wheel. Mr Thomas thought of mounting several images on to a board as a collage, an idea he said Mr Withnall welcomed.
"He helps with the gluing and puts the shapes where he wants them."
This year, for the first time, Mr Withnall has a collage entered in the IHC art awards which have been held annually since 2004.
Mr Thomas said he was not sure disabled people who had an artist helper were eligible to enter and was pleased to discover they were.
The work Mr Withnall had entered took about 40 hours to complete and deserved to be exhibited and judged, he said.
He said he had never worked with disabled artists before and was learning to be patient.
"I am working with two people... and they both devote themselves to a subject. It is a long drawn-out process to complete a work, but their enthusiasm for their art speaks volumes."
The art awards, which offer a $5000 first prize, are divided into three regional heats. Dunedin is hosting the South Island heat for the first time. Paintings, drawings, mixed media works and photographs from 110 artists are on display at Art Space, 286 Princes St, until June 27.
The national winners will be announced in August.
