It is the main route from Helsinki to Northern Finland and a major road link in the country.

The road is 1,295 kilometres (805 mi) long, making it Finland's longest highway.

The route of the road is Helsinki – Lahti – Heinola – Jyväskylä – Äänekoski – Oulu – Kemi – Rovaniemi – Sodankylä – Ivalo – Inari – Utsjoki.

The original highway 4 ran from Helsinki to Petsamo before World War II.

Since the end of the war, the road has been rerouted to Ivalo and Karigasniemi on the Norwegian border.