§ 1142. Vehicle entering stop or yield intersection. (a) Except when directed to proceed by a police officer, every driver of a vehicle approaching a stop sign shall stop as required by section eleven hundred seventy-two and after having stopped shall yield the right of way to any vehicle which has entered the intersection from another highway or which is approaching so closely on said highway as to constitute an immediate hazard during the time when such driver is moving across or within the intersection.

(b) The driver of a vehicle approaching a yield sign shall in obedience to such sign slow down to a speed reasonable for existing conditions, or shall stop if necessary as provided in section eleven hundred seventy-two, and shall yield the right of way to any pedestrian legally crossing the roadway on which he is driving, and to any vehicle in the intersection or approaching on another highway so closely as to constitute an immediate hazard during the time such driver is moving across or within the intersection. Provided, however, that if such driver is involved in a collision with a pedestrian in a crosswalk or a vehicle in the intersection after driving past a yield sign without stopping, such collision shall be deemed prima facie evidence of his failure to yield the right of way.