U.S. Route 6 is also known as the Grand Army of the Republic Highway. It is 5,158 kilometers (3,205 mi.) long, and was constructed in the honor of the American Civil War Veterans Association in the 1920s. The road runs from Bishop, California, going east-northeast to end up at Provincetown, Massachusetts.
Starting at an intersection with U.S. 101 at Newport, Oregon, it runs through nine states, before ending at Boston, Massachusetts. It is the longest road in the United States, and is also a very scenic drive, especially as one passes through Yellowstone National Park.
The longest highway in India, the Golden Quadrilateral connects four most major cities of the nation (Kolkata, Delhi, Mumbai, and Chennai). The highway was constructed on a budget of 600 billion INR, between 2001 and 2012. Spread out across the country, the total length of this highway is 5,846 km (3,633 mi.).
With a length of around 7,821 kilometers (4,860 mi.), the Trans-Canada Highway is 4th longest in the world, and passes through each of the ten provinces of Canada, connecting all the major cities in the country. Construction of the project started in 1950, and ended in 1971, with a cost of approximately USD 1 billion.
The road travels across the coastal area of the Australian mainland, touching all states, save Brisbane and Darwin, and carries over a million travelers each day.
It connects northern Canada to southern Argentina, taking one through a wide variety of climates, topographies, and cultures, making it a really interesting journey, meant only for the most adventurous travelers.
It is expected to be around 20,000 kilometers (12,427 mi.) long, starting from Britain, running all across Russia, and meeting Alaska in the United States at the Bering Strait. If completed, It will be one of the most ambitious projects undertaken in human history.