The D.C. Metro system was planed in the &#x27;60 and constructed in the &#x27;70s, with the first operations starting in 1976.  It too is based on electro-mechanical relays, although it&#x27;s more ambitious, after the operator closes the doors and sees all is fine, he hits a &quot;go&quot; button and the system automatically takes the train to the next station, avoiding collisions as long as the &quot;is there a train in the next segment&quot; sensor system is working.