There numerous ways how to do this. I'll help you with two types. The first one is the easiest for your type of map.

Preview 1
Road_Preview_1.jpeg
This one is simple. Pick a round brush, pick your color that would fit your map. Then change your brushes SPACING to be much larger. And then you literally just draw the line and the dots would be evenly spaced as long as you draw.

Preview 2
Road_Preview_2.jpeg

This one is a bit more complicated. Pick a cloudy brush, something that doesn't have a hard edge. Pick your color for the road, something that would fit. And then you draw your road. ON ITS OWN LAYER. When you have your road outline, you select the road. And stroke selection with a lower opacity brush that is darker. BECAUSE you have the road selected the shadow would just appear on top of the road, but you are brushing the sides. (Okay, simplistic language, you paint the sides of the road in a darker lower opacity brush to give a shadow effect.)