A road marking unit (1) according to the invention comprises a house (10) with a light transmissive window (20). In the house (10) is arranged an electro-optic switch (30). In an activated state of the road marking unit (1) the electro-optic switch (30) achieves that light is reflected from the window (20) back to the window (20). In a de-activated state of the road marking unit (1) the electro-optic switch (30) achieves that light from the window (20) is absorbed. The road marking unit (1) of the invention has the advantage that it can also in bright environmental light be switched between visible and invisible.