Where preference is given to traffic through any intersection on any roadway and specified entrances to said intersections are designated as yield right-of-way entrances by the erection of yield right-of-way signs or signals in the parking area, the driver of a vehicle in obedience to a yield right-of-way sign or signal shall slow down to a speed reasonable for the existing conditions, or shall stop if necessary, and shall yield the right of way to other vehicles which have entered the intersecting roadway either from the right or left of which are approaching so closely on said intersecting roadway as to constitute an immediate hazard, but said driver having so yielded may proceed at such time as a safe interval occurs.
Appropriate yield signs or signals shall be erected in conformity with the Plan.