The Main road 21 is a southâÂÂnorth direction First class main road in the valley of the Zagyva river, that connects the Hungarian M3 motorway's Hatvan junction, facilitating access from the capital city of Hatvan to Salgótarján-Somoskà Âújfalu. The road is 65 km long.
The road, like all other main roads in Hungary, is managed and maintained by the state-owned company Magyar Közút.