More lanes or more roads?

[aww999]

Foolowing on from the M25 widening topic, I was wondering. Given that lane disciplin is so poor, and that congestion results when a multilane section goes to a narrower section of motorway;

Would it be a more advantageous use of tarmac area to build more major roads to places using different routes, rather than widening the ones we already have?

ie would two three lane roads carry more traffic than one six lane road?