Are you allowed to make a U-turn on a roadway with this sign?

In the photo, on the right-hand side there is a round blue sign with a white arrow pointing up - this is sign C-5 "go straight ahead". It orders you to drive only straight on, so it rules out turning and making a U-turn. Since you must not change your direction of travel on this roadway, a U-turn is prohibited.

Mandatory signs C-1 to C-11 require the driver to move in the direction shown by the arrow and apply at the nearest junction or at a place where it is possible to change direction. A U-turn is a change of direction of 180 degrees, which is exactly what sign C-5 prohibits. In addition, the road in the photo runs along an elevated roadway, and making a U-turn on a bridge or flyover (viaduct) is prohibited by a separate rule of the Road Traffic Act.

Legal basis: § 35 para. 1 and 2 of the Regulation on road signs and signals; Art. 22 para. 6 point 1 of the Road Traffic Act (Prawo o ruchu drogowym)