Abstract: A cover for a road system device provided with a frame comprises: a blocking member and a base body defining a covering surface for the road system device, extending in a cover plane, and having a housing for receiving the blocking member. The housing and the blocking member are adapted for blocking the cover relative to the frame or to a neighboring cover. The housing is adapted to maintain the blocking member relative to the base body autonomously and to oppose a movement of the blocking member in a direction extending perpendicular to the cover plane and tending to move the blocking member away from the covering surface. The invention is applicable to access manholes for underground installations.