In this situation, are you approaching a crossroad with a side road?

In the video you are driving on a street in a housing estate of blocks of flats in town; on the right there is sign D-1 "priority road" with plate T-6a, on which the thick line turns left and the thin line branches off to the right. You are approaching a junction with a minor road. The answer is: yes.

The Regulation on road signs and signals states that sign D-1 marks the beginning or continuation of a priority road, and plate T-6a shows the actual course of the priority road through the junction: the priority road is marked with a thick line, the minor roads with thin ones. Since there is a thin line on the plate, a minor road joins at the junction; its entry is marked with sign A-7 or B-20, and vehicles coming out of it must give way to you. Sign D-1 alone is enough to know that every road joining yours at the nearest junction is a minor road - the plate only shows which one it is and which way the priority runs. Here the priority road turns left, so if you follow the thick line, you keep right of way over vehicles from the right; if you went straight on or right, you would leave the priority road. You approach the junction with particular caution, watching the entry of the minor road.

Legal basis: § 43 para. 1 and 2 of the Regulation on road signs and signals; Art. 25 para. 1 of the Road Traffic Act (Prawo o ruchu drogowym)