[Tamlin]

Well, I had a go. It's straight off the top of my head, so it's not perfect and I'm sure it can be done a lot better with some other technique, but here goes:

1. Create a new file with a white background. I made mine 500x500.

2. Create a new layer, press "D" to select default colours, then select the Rectangle Tool. Make sure Fill Pixels is selected, and it's probably a good idea to turn off Anti-Alias.

3. Draw a black rectangle that almost fills the layer (see attached File1)

4. Make another new layer. Make white the foreground colour, then (still using the Rectangle Tool) draw a narrow rectangle down the middle of the black one (see File2).

5. Next, select the Eraser tool. From the Brush drop-down menu, load Square Brushes and choose one that is slightly wider than your white rectangle.

6. Erase sections from your solid white rectangle to give you a broken white line (see File3).

7. Make sure you still have the white line layer active, then select Layer > Merge Down. You now have the black road and the white line as a single object on their own layer. Now you can use any of the Transform tools to stretch the road object to simulate the effect of perspective. You could even use the Warp tool to put some bends in the road. File4 shows what I did with the Skew and Scale tools.

As it's an object on a separate layer, you can drag it into another image if you want to.

As I said, it's far from perfect, but I hope it gives you some ideas, anyway.