New Yorkers were treated to a free exhibition of four of BMW's most famous Art Cars, which were part of a display in Grand Central Station last week. Over the years, leading artists have been commissioned to paint whatever they wish on a car and many have accepted, from Alexander Calder to David Hockney. There are 16 cars currently in the collection.

It all started when French racing driver and art dealer Herve Poulain induced Calder to paint a car that he was driving at Le Mans. BMW corporate became interested, and new works have been commissioned periodically ever since.

For the Grand Central exhibition, four cars were chosen, each painted by a renowned American artist with a deep connection to New York. Frank Stella, Roy Lichtenstein, Robert Rauschenberg and Andy Warhol have all produced artworks which have sold for millions of dollars each.

In 2007, a single canvas by Warhol called Green Car Crash fetched more than $70 million at auction, despite the fact that he produced several versions of the canvas. What would a unique work such as Warhol's 1979 M1 fetch on the open market? The cars will never be sold, but it's possible that these are the most valuable vehicles on the planet.

The Stella car, a 1976 3.0CSL, is hand-finished like a massive sheet of graph paper. A close examination reveals that the lines of the graph stand up on the surface of the bodywork, which must have been less that optimal when the car competed at Le Mans. However, the finish is simply perfect compared with the Warhol M1, which was painted using a large housepainter's brush, the paint applied thickly to the bodywork, rutted visible brush marks everywhere in the car.

Lichtenstein, one of the fathers of Pop Art, finished his 320i with his trademark dots and flowing stripes, with a perfect, jewel-like finish. Rauschenberg used antique china patterns on his white 635 CSi.

None of the cars is identical on each side, and each richly rewards extended viewing.

The exhibit also included a new work by artist Robin Rhode in which a 2009 Z4 was equipped with paint dispensers behind each wheel and driven around a huge white sheet, creating a vivid vista of abstract tire patterns.