So I've bitten the bullet and built the access road. There were two reasons I wasn't particularly looking forward to this bit. Firstly I wasn't sure what I was going to use as the road surface, but more importantly fitting the road would mean permanently incorporating the road bridge into the layout. In other words, if I messed up I'd have to build the bridge all over again, and as I've mentioned before it isn't the easiest of things to construct.
After my success with building the loading dok top, I decided to make the road surface out of the same air drying clay (it's a commonly available modelling clay called DAS but I can't seem to find a manufacturers website). As you can see it is now in place and painted. I tried to keep the colour from becoming too uniform by again painting with the slate gray pigment and then washing on black. As the surface is smoother though, it seems that the black wash has given a more even colouring, although it still has some variation.
The next job is to to extend the surface around the factory building to form the yard area. Once that is done I should then be able to finish ballasting the siding and fix the point lever in place. After that I think I can make a start on the more natural parts of the landscaping; grass, trees, etc.