What are "flying cars"?

I'm reading Peter Dougherty's book, TRACKS OF THE New York City SUBWAY (2013). While describing the then-future Second Avenue Subway, he states:

The final phase will complete the 8.5 mile line's run down to Hanover Square in the financial district providing four new stations. Plan for this is to coincide with the introduction of flying cars.

So what is a flying car?

A bit of sarcasm regarding the glacial pace at which the Second Avenue Subway progresses. We're two years away from the centennial anniversary of its proposal and five years away from fifty years after the initial halting construction began in the 1970s.

Basically

Where we're going, we don't need roads!
https://www.youtube.com/watch?v=LKLs9ynZEH0" onclick="window.open(this.href);return false;
(That was 2 years ago, BTW)