cheers mat again the basic rules are fairly simple, the hard part was learning about goalU and goalV targets on curves/surfaces and manipulating them so the particles sat in the right positions
The generation of different cars/trucks/bikes etc will be a simple little instancer script or similar. If I can figure it out then there will be controls to add weightings - e.g, have 50% trucks, 40% cars and 10% others etc and move these about to get the desired effects.

thanks arran, glad you both like it
yeah the lane changing will be interesting - I know what it needs to do but getting it to work will be a bit of a challenge!