▁not ▁meet ▁current ▁standards , ▁however ▁it ▁would ▁be ▁prohib it ively ▁expensive ▁to ▁immediately ▁re build ▁them ▁all ▁to ▁updated ▁gu idel ines , ▁unless ▁a ▁reconst ruction ▁is ▁war r anted ▁by ▁safety ▁concerns ▁and ▁traffic ▁levels . ▁As ▁a ▁result , ▁sub standard ▁sections ▁of ▁fre ew ays ▁such ▁as ▁low ▁over pass es ▁and ▁short ▁acceleration / de cel er ation ▁lan es ▁are ▁often ▁retro f itted ▁with ▁guard ▁rail , ▁warning ▁sign age , ▁lower ▁speed ▁limits , ▁or ▁light ing . ▁ ▁The ▁United ▁States ▁Federal ▁Communic ations ▁Commission ▁has ▁required ▁all ▁radio ▁stations ▁lic ensed ▁in ▁the ▁United ▁States ▁since ▁the ▁ 1 9 3 0 s ▁to ▁have ▁four - letter ▁call ▁signs ▁starting ▁with ▁a ▁W ▁( for ▁stations ▁east ▁of ▁the ▁Mississippi ▁River ) ▁or ▁a ▁K ▁( for ▁stations ▁west ▁of ▁the ▁Mississippi ▁River ). ▁But ▁stations ▁with ▁three - letter ▁call ▁signs ▁and ▁stations ▁west ▁of ▁the ▁Mississippi ▁River ▁starting ▁with ▁a ▁W ▁and ▁east ▁of ▁the ▁Mississippi ▁River ▁starting ▁with ▁a ▁K — such ▁as ▁W R R ▁in ▁Dallas ▁and ▁WH B ▁in ▁Kansas ▁City , ▁plus ▁K Q V ▁and ▁K Y W ▁in ▁Pennsylvania , ▁all ▁lic ensed ▁before ▁the ▁ 1 9 3 0 s — have ▁been ▁permitted ▁to ▁keep ▁their ▁call ▁signs . ▁In ▁the ▁western ▁United ▁States , ▁K O A ▁in ▁Den ver , ▁K GA ▁in ▁Sp ok ane , ▁K EX ▁in ▁Port land , ▁and ▁K H J