▁a ▁measure ▁of ▁traffic ▁volume ▁for ▁any ▁average ▁day ▁of ▁the ▁year . ▁In ▁ 2 0 1 1 , ▁W SD OT ▁calculated ▁that ▁the ▁bus iest ▁section ▁of ▁the ▁highway ▁was ▁between ▁SR   3 ▁and ▁Liber ty ▁Bay , ▁serving ▁ 1 1 , 0 0 0 ▁vehicles , ▁while ▁the ▁least ▁busy ▁section ▁was ▁the ▁bridge ▁over ▁Liber ty ▁Bay , ▁serving ▁ 6 , 3 0 0 ▁vehicles . ▁ ▁History ▁ ▁The ▁current ▁route ▁of ▁SR   3 0 8 ▁was ▁first ▁added ▁to ▁the ▁state ▁highway ▁system ▁in ▁ 1 9 2 9 ▁as ▁the ▁Key port ▁branch ▁of ▁State ▁Road   2 1 ▁and ▁was ▁carried ▁over ▁to ▁the ▁primary ▁and ▁secondary ▁state ▁highway ▁system ▁in ▁ 1 9 3 7 ▁as ▁a ▁branch ▁of ▁P SH   2 1 . ▁The ▁branch ▁tra ve led ▁ ▁east ▁from ▁P SH   2 1 ▁near ▁Naval ▁Sub marine ▁Base ▁Bang or ▁to ▁the ▁Naval ▁Under se a ▁War fare ▁Center ▁in ▁Key port , ▁intersect ing ▁Second ary ▁State ▁Highway   2 1 B ▁( SS H   2 1 B ) ▁before ▁crossing ▁Liber ty ▁Bay . ▁The ▁Key port ▁branch ▁was ▁incorpor ated ▁into ▁SR   3 0 3 , ▁which ▁replaced ▁SSH   2 1 B , ▁with ▁a ▁short ▁sp ur ▁route ▁serving ▁Key port . ▁SR   3 0 8 ▁was ▁established ▁in ▁ 1 9 7 1 ▁to ▁replace ▁the ▁Key port ▁sp ur ▁of ▁SR   3 0