ruction ▁and ▁do ▁not ▁exceed ▁the ▁speed ▁limit ▁for ▁any ▁segment ▁of ▁track . ▁The ▁system ▁stops ▁trains ▁in ▁advance ▁of ▁any ▁other ▁train ▁traffic , ▁and ▁before ▁stop ▁signals ▁at ▁inter lock ings . ▁The ▁cab ▁sign alling ▁system ▁re lies ▁on ▁track ▁circ uits ▁to ▁detect ▁track ▁occup ancy , ▁and ▁thus ▁send ▁the ▁appropriate ▁speed ▁code . ▁Although ▁the ▁ATP ▁system ▁was ▁designed ▁to ▁be ▁fail - safe , ▁the ▁track ▁circuit ▁control ▁equipment ▁on ▁which ▁it ▁re lies ▁has ▁been ▁pr one ▁to ▁par as it ic ▁oscill ations ▁which ▁can ▁cause ▁the ▁system ▁inter mitt ently ▁to ▁fail ▁to ▁detect ▁the ▁presence ▁of ▁a ▁train . ▁This ▁resulted ▁in ▁the ▁ 2 0 0 9 ▁collision , ▁after ▁which ▁Metro ▁began ▁to ▁operate ▁all ▁trains ▁manually . ▁In ▁September ▁ 2 0 1 4 , ▁Metro ▁began ▁re int rodu cing ▁its ▁computer ized ▁control ▁system ▁after ▁taking ▁a ▁number ▁of ▁measures ▁to ▁avoid ▁acc idents ▁similar ▁to ▁the ▁ 2 0 0 9 ▁accident . ▁ ▁The ▁Autom atic ▁Train ▁Super vision ▁sub - system ▁provides ▁for ▁head way ▁management ▁and ▁proper ▁inter le aving ▁of ▁trains ▁at ▁j unction s ▁by ▁speed ing ▁up ▁or ▁slow ing ▁down ▁trains . ▁The ▁system ▁works ▁via ▁a ▁series ▁of ▁track ▁mounted ▁bal ises , ▁which ▁function ▁as ▁information ▁be a cons ▁transm itting ▁a ▁speed ▁code ▁to ▁the ▁train ▁as ▁it ▁passes ▁overhead . ▁Its ▁design ers ▁intended ▁its ▁function ▁to ▁be ▁non - v ital , ▁and