D21 road (Croatia)

D21 was an 80.1-kilometre-long (49.8 mi), north–south state road in Istria County, Croatia. A short section of D21 was part of the European route E751. The northern terminus of the route was located at the Croatia–Slovenia border at the Dragonja River. There it connected to Koper, Slovenia, and Trieste, Italy, via the Slovene route G11 further north. The route was generally parallel to A9 motorway, with which it formed several junctions, either directly or via short connectors, at Buje, Bale and Vodnjan – towns served directly by D21. The southern terminus of the route was found in the city of Pula, at the southern tip of the Istrian Peninsula.

The road, as well as all other state roads in Croatia, was managed and maintained by Hrvatske ceste, a state-owned company. The road carried an annual average daily traffic of about 2,000 vehicles, and the traffic volume increased by up to 1,000 vehicles in summer as the road was used by tourists in the region. The southernmost portion of the road was significantly more congested as it carries Pula suburban traffic.

In classical antiquity, the western Istria route was first used by Via Flavia in the classical antiquity, but the roads in the area declined in the Middle Ages and subsequent division of the Istrian Peninsula by the Republic of Venice and the Habsburg Empire was not conductive to development of a road system. In the 19th century, the First French Empire started road construction, including the Trieste–Pula route now largely followed by D21. The route was a part of M2 Adriatic Highway route after the Second World War. It was made a separate state road and assigned the D21 route number in 1997. In 2013, the road was abolished because of the creation of parallel D75 road, located west of the A9 motorway.