London and Budapest had subways before Boston did. So did some other cities depending on which list you look at. So what made Boston’s later entry the first “

London and Budapest had subways before Boston did. So did some other cities depending on which list you look at. So what made Boston’s later entry the first “practical” one? [Edit] Or do you mean self-driving subways? Does Boston have one already? A quick Googling suggests the opposite: https://whdh.com/news/mbta-officials-considering-self-driving-subway-cars/ https://whdh.com/news/mbta-officials-considering-self-drivin...