▁ 1 9 2 6 , ▁with ▁full ▁ad option ▁made ▁in ▁ 1 9 3 0 . ▁Col our ▁light ▁signals ▁first ▁appeared ▁in ▁ 1 9 1 8 , ▁and ▁by ▁ 1 9 2 4 ▁they ▁were ▁the ▁standard ▁for ▁new ▁install ations . ▁ ▁The ▁saf ew ork ing ▁of ▁trains ▁between ▁stations ▁on ▁the ▁early ▁lines ▁was ▁time ▁interval ▁working , ▁where ▁a ▁train ▁would ▁be ▁allowed ▁to ▁leave ▁a ▁given ▁time ▁after ▁the ▁train ▁before ▁it . ▁With ▁heav ier ▁traffic ▁this ▁method ▁became ▁unsafe , ▁with ▁Staff ▁and ▁T icket ▁working ▁on ▁single ▁lines ▁adopted ▁from ▁ 1 8 7 3 , ▁and ▁te legraph ▁block ▁working ▁from ▁ 1 8 7 8 ▁on ▁double ▁lines . ▁Both ▁of ▁these ▁systems ▁ens ured ▁that ▁only ▁one ▁train ▁would ▁be ▁in ▁a ▁section ▁of ▁track ▁at ▁one ▁time . ▁Te legraph ic ▁block ▁working ▁was ▁then ▁replaced ▁with ▁Winter s ▁Block ▁working ▁between ▁ 1 8 8 3 ▁and ▁ 1 8 8 8 , ▁a ▁system ▁that ▁is ▁a ▁prede cess or ▁of ▁the ▁Double ▁line ▁Block ▁system ▁which ▁is ▁still ▁used ▁today . ▁Later ▁years ▁saw ▁variations ▁made ▁to ▁the ▁Staff ▁and ▁T icket ▁system , ▁with ▁bus ier ▁lines ▁provided ▁with ▁Electric ▁Staff ▁working ▁which ▁provided ▁greater ▁safely ▁when ▁more ▁trains ▁ran . ▁ ▁He avier ▁sub urban ▁traffic ▁on ▁the ▁Melbourne ▁network ▁saw ▁a ▁greater ▁stra in ▁on ▁the ▁block ▁working ▁then ▁used , ▁which ▁required ▁a ▁large ▁number ▁of ▁man ned ▁signal