Copy and paste/duplicate?
Draw a line in the center of the road.
Apply a thick stroke
Object > Path > Outline stroke
I need two seprate paths, so I can edit the bottom curve and make a curve at the two intersecting roads. Is there a feature in illustrator like DimCurves?
Can you please show a sketch of what this is to look like when finished?
I found out the tool I was looking for it was Object->Path->OffsetPath
Iwas hesitant to recommend offset path, because I wasn't sure you have a closed path there.
You might perhaps want to try out the plugin Toolshed, which can offset open paths: https://rj-graffix.com/downloads/plugins/#toolshed