"Rolling Stock"......... Did I use that one yet?

Well, I've finished modelling the 3 different detail levels for my train.

Low detail (500 poly):

It took me so long to get the model under the poly limit and looking the right shape. I was quite proud of it once it was done.
I think I saved myself some hasle without realising it, as I had designed my vehicle to have many 'faceted' faces, which meant that I didn't need to use any smoothing to get my desired result.

Medium detail (2500 poly):

The mid level poly model I found the easiest of the three to complete. I started from scratch rather than build from the low poly model, as I had simplified a lot of the shapes of the vehicle to fit it under the low poly limit.
This allowd me to more closely match the shape of my design sketches.

High detail (5000 poly):

I struggled again with the high poly model. This time I started with the previous model (mid-poly) and built up the detail in several areas. The first area that got more detail attention was the front wheels of the train, which were supposed to be big tyred wheels like those of a monster truck. then I added a small amount of detail to the tank track wheels. the main improvement to all of the wheels was the upping of their subdivisions from 8 to 16, making them appear much rounder. I failed to improve the detail on the tracks very much as when I tried to extrude the faces out to make them look smoother, I rapidly exceeded the poly limit. So I instead improved teh detail of the two chimneys, the cockpit windows and the railing at the back of the train. I also added a small ladder and door to the rear of the cockpit.