In this situation, are you warned of road narrowing that may impede traffic?

In the video, you are driving on a road through maize fields which, beyond the sign, enters an avenue of trees; on the right there is a yellow triangle A-12a "road narrows - on both sides". You are warned of a narrowing of the roadway which may impede traffic. The answer is: yes.

The Regulation on road signs and signals states that signs A-12a, A-12b and A-12c warn of a narrowing of the roadway on the side shown on the sign, which may impede traffic; A-12a refers to a narrowing on both sides. Whichever side the roadway narrows on, the meaning of the warning is the same: further on there will be less room than you have now, so there may not be enough room to pass an oncoming vehicle or to overtake a cyclist with the required clearance of one metre. The sign does not set right of way - only signs B-31 and D-5 do that at a single-lane narrowing; here both drivers must work it out between themselves, and the Road Traffic Act requires you, when passing an oncoming vehicle, to keep a safe distance and, if necessary, move to the right, reduce speed or stop. Warning signs require you to exercise particular caution - beyond the sign you take your foot off the accelerator, watch for traffic coming from the opposite direction and do not start overtaking.

Legal basis: § 7 para. 3 and § 3 para. 1 of the Regulation on road signs and signals; Art. 23 para. 1 point 1 and Art. 24 para. 2 of the Road Traffic Act (Prawo o ruchu drogowym)