What we are trying to do is take a "road" made of quads like the following, and widen it to where the green grease marks are:
The problem is that if you simply scale it, you get a mess:
So, there are two ways to fix it.
Script Way(Edit)
One solution is to use the "Inset Outline" script from here: http://panoptic.com/rking/blender/inset_outline.py with a negative value to make it Outset instead of Inset.
Manual Way(Edit)
Another solution involves scaling along some normals, using a temporary Solidify modification and then Alt+s.
1. Duplicate the road (Alt+d)
2. Solidify the shape by extruding it downwards.
3. In Face Select mode (Alt+Tab, F), and Alt+RMB to select the sides:
4. Scale them according to normals with Alt+S:
5. Delete the ring (which should still be selected):
6. Select the extra chain of faces with Alt+RMB, and delete them, too.
7. Make sure both roads have their origins in the middle, by Ctrl+Shift+Alt+C > Origin to Geometry
8. Hit 'n' to bring up the Properties panel, and Copy the Z value from the skinny road (Hover over the value and hit Ctrl+C):
9. Paste it onto the Z value of the fat road:
10. And enjoy!
7.