Proposals for "quadraplex" articulated locomotives:
http://www.dself.dsl.pipex.com/MUSEUM/LOCOLOCO/quadruplex/quadrapl.htm
http://www.dself.dsl.pipex.com/MUSEUM/LOCOLOCO/quadruplex/quadrapl.htm
it is not suprising that these designs werent popular. The reality is double heading is much easier, more versatile, and just plain makes more sense.
Kevin
The problem with double heading is that each steam engine required an engine crew to operate it. If the railroads could design a double or triple sized locomotive that could operate with one crew, they could save on labor costs. Labor costs were so low in the 19th and even early in the 20th century that it wasn't an issue, but by the late 1920's & 1930's union contracts were beginning to cause wages to rise. I suspect that the ability to hook diesels into mu consists with one operating crew had as much to do with the end of steam as the lower maintenance costs of diesel.