Possibly the longest road on the planet?

Since the Conference of American States in 1923 there have been plans to build a Pan-American Highway - a continuous roadway running the full 25,800km (16,000 mi) from Alaska to the bottom of Chile. Now, all but 88km (54mi) are complete, so aside from a time-consuming detour, it's possible to drive from above the Arctic Circle down to Puerto Montt, nearly 1000km (600mi) south of Santiago, Chile.

Although the Pan-American Highway, or Interamericana (a.k.a Panamericanan & Pan-1), is more of a concept than an actual route, most say that it starts in the tiny Alaskan town of Circle, some 150km (93mi) west of the Canadian border and about 100km (62mi) south of the Arctic Circle (from which the town gets its name). Since 1994, however, the Dalton Highway has allowed drivers the option of starting their trip further north, from the shores of the Beaufort Sea in Deadhorse.

Pan-American Highway crosses the following countries: Canada, USA, Mexico, Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, Panama, Colombia, Ecuador, Peru, Chile and Argentina.

More information :
Definition of Pan-American Highway in online encyclopedia
Pan-American road trip description from Lonely Planet