The D3 motorway (Czech: Dálnice D3) is a highway in the Czech Republic. Currently only some segments of the route are in operation; when complete, it will run from Prague through Tábor and České Budějovice to the Czech-Austrian border at Dolní Dvořiště. It is part of the European route E55.
The D3 motorway in the South Bohemian Region towards the Austrian border should be completed by 2024. Completion of D3 in the Central Bohemian Region is planned by 2028.
Once completed, the 172-kilometre-long (107 mi) highway will connect the Czech capital Prague with the Austrian Mühlviertler Schnellstraße (S10) highway to Linz. As of December 2019 only 69.6 km (43.2 mi) of the highway are in operation, a section from Mezno to Úsilné, while a further 19.7 km (12.2 mi) from Úsilné to Dolní Třebonín are currently under construction. The most controversial and disputed section is the planned segment in the Central Bohemian Region.
A 24.0-kilometre-long (14.9 mi) section from Dolní Třebonín to the border with Austria on the other side of the future Mühlviertler Schnellstraße (S10) was initially planned to be built as an expressway (Czech: rychlostní silnice), however on 1 January 2016, the category of expressways was abolished, and it is counted as part of the D3 motorway.