the longest road in the world is in Americas. The longest road is a highway called Pan American highway. It spans 30000 Kilometers or 19000 miles. It starts from Prudhoe Bay, Alaska in United states and ends at Puerto Montt or Quellón, Chile Chile or Ushuaia, Argentina Argentina

The pan american highway is registered as longest road in the world in guiness book of world records 

There are also other categories of longest road in the worlds like Asian highway which starts in Kapıkule, Turkey and ends in Tokyo, Japan. Asian highway is longest uninterrupted highway in the world. Length of the asian highway is 20557 Kilometers or 12774 miles

Longest road within the single country is in Australia. The name of the road is Highway 1. This is loop road and legnth of the highway is 14500 Kilometers or 9000 miles