If we're going to need these trains in a "decade or two" we need to start building now.  Short sightedness has left us with a real mess already.  And self-driving cars are the current day dream - they will never be realistic as long as they mix with human driven cars - humans can't be counted on to always react as expected.  That doesn't mean the humans are wrong - and accidents happen because of many factors - human actions both cause and prevent accidents.  We are not ready with an AI that can anticipate human reactions well enough to allow it to control a weapon on our streets (which cars most definitely are).