use the path tool to creat a path. then edit>stroke path. you will get options as to width and style (dashed lines etc.)

to outline the road. select it using the fuzzy select tool. create a new layer. grow selection by one then fill with the desired color. move the layer down and you will have the road outlined with the new color.

the key is to use lots of layers, you can always merge them down when they look right.