Laying the foundation
The first thing to decide is what type of road you are having, single or double carriageway, country lanes or narrow streets. All will require different widths and surfaces. Vary your shades to highlight the weathered look of the tarmac.
Making white lines
Decide on the width and length of your lines and lay masking tape down on the surface. Lightly paint the white line over the masking tape making sure to not use too much as the lines are generally worn.
Add a pavement
Particularly key in town settings where pavements are prominent. Slabs can be engraved into DAS clay on top of plywood. In the country, leave a thin flatter strip at the edge of the road indicating walkers have been through.
Model a pedestrian crossing
In town scenes, a pedestrian crossing gives a viable point to explain figures on both sides of the road. Consider dropped kerbs and barriers, as well as stop lines for traffic. Zebra crossings will also require beacons.
Get the Gear
Mark out your road with a flexible curve and white marker pen. Take care to draw all your lines the same length, as without tape as a guide you could end up with uneven lines that will distort the appearance.