With this amount of detail it was difficult to keep the originality, the details and the shapes consistent. To help, I played with the Deformation modifier in Max, which is a very useful way of creating a new concept. You can use Symmetry, Twist, Bend or all of them together and from a basic mesh you can obtain a new concept with new shapes and details (Fig.04).
The car was made with the theme of Paris in mind too. I went with an old European sedan from the 30s, like a Lancia, Talbot, Delage or Mercedes. I added two big reactors at the front. For the modeling, there was nothing special; it's always a pleasure to make a car as there's something magical in modeling automotive design (Fig.05).

Fig. 05
Organization
This type of the scene can cause problem with the polygon density and the number of objects. At the beginning all the modeling was done independently and with a maximum number of modifiers to permit quick correction. When I finished the modeling I merged all my objects by materials or the same element type to increase the unfolding texturing speed.
For the organization of the layers I used the same as my level of details divided into two parts: meshes and lights, with a more few layers like "train" (Fig.06).

Fig. 06
Texturing and Shaders
After I completed the organization of my scene, I couldn't waste time with unfolding the UVs and the texturing, but I also didn't want to lose the quality.
The V-Ray blender was very useful here; I was able to blend some different shaders for each part of the final material (metal, rust, dirt, water, etc). When all the shaders were ready I just needed to put a tileable noise map as a mask in the blending slot and play with the tiling and offset values (Fig.07). Using this system there are a lot of possibility with a single map; imagine what you could do with five or ten!

Fig. 07