This hex terrain system is compatible with both 15mm and 20mm miniatures. In 15mm the road width is aprox 24 feet wide, in 20mm it is aprox 18 feet wide, both very acceptable widths for 2 lane roads.
These hex pieces are precision laser cut from 1/8" (3mm) MDF, not the brittle foam material you may be used to seeing from other manufacturers. You can add foam to the top of these hexes to create elevated terrain (hills, etc) and still have a durable MDF base that will stand up to years of continued use.
The hexes with roads on them come with pre-cut sidewalks, all you need to do is glue them on, paint them and add whatever ground covering you like to the other areas. Leaving the sidewalks off allows you to paint them separate from the road area and then glue them on insuring a perfect paint job without any masking or accidentally getting road paint on the sidewalks or vice versa. The hexes have engraved lines to assist you in locating exactly where the sidewalk pieces attach.