Thanks to all for the comments and examples - way over my skill level at the moment.
So it took me a week or two (well month - blush) to get around to trying out my idea and the first test results are not too bad (and I learnt a lot)
10 sheets of Wilkos
400 grit wet and dry - a bit small (140mm X 230mm) but as my board is only 2x2 I can get two or three 6" or 8" lengths out of one sheet so not too bad for £3.50 - cheaper then eBay or a trip to the market in town.
The scuffing up I did before the varnish hardly shows (even in real life) so I need to add more contrasting light and dark patches.
The lines are nail tape off eBay - I ordered white and yellow from '
electric transport' and they kindly sent a couple extra strips (now heading to my daughter as they clash with my eyes). Turns out they stick fine to nails, themselves, the desk, my mouse (do not ask) and even my chocolate bar but not to wet and dry sandpaper!
I used spots of mod-podge to hold them and then sprayed with cheap matt varnish to hold BUT they reacted with the spray (propellant or contents - unsure at the mo) and stretched in a few places, lifting off in a little (about 1mm high) bumps:

Very odd - I am 100% sure they where flat to the paper when they got sprayed and straight after and was not left in the sun to dry so it must be a reaction to the varnish. The glue was not in the places the bum,bs are so its not that.
I had planned on using the steps down the middle of the road (just to break up the large grey / black strip) but think I may just cut two strips per road section and leave a gap between showing the white plastic card I'll stick these on. The plastic is needed as, even after the varnish, the sheets are bendable and slightly warped.
I may try once more with mod-podge all the way down the strip as I like the yellow / gold tape effect...
Fortunately, the scenarios out of the One Hour Wargames book all have straight roads (oh and a cross road) so I do not have to work out how to cut parallel curves (or stick the tape in a bend) yet!