Section 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.