(a) The driver of a vehicle shall stop as required by section five, article twelve of this chapter at the entrance to a through highway and shall yield the right-of-way to other vehicles which have entered the intersection from said through highways or which are approaching so closely on said through highway as to constitute an immediate hazard, but said driver having so yielded may proceed.
(b) The driver of a vehicle shall likewise stop in obedience to a stop sign as required herein at an intersection where a stop sign is erected at one or more entrances thereto although not a part of a through highway and shall proceed cautiously, yielding to vehicles not so obliged to stop which are within the intersection or approaching so closely as to constitute an immediate hazard, but may then proceed.