roving herds of dangerous cars

Modern society is infested with dangerous parasites called cars. Cities, places designed to be the home of thousands or millions of people, have been slowly reshaped to make life easier not for their inhabitants but for cars.
Streets, which used to connect places, are now moats filled with fast moving metal beasts which threaten to kill innocent pedestrians and cyclists.

This is also a theme that turns up on occasion in science fiction. From Keith Laumer's Bolo series about intelligent tanks to Roger Zelazny's classic short stories "Devil Car" and the sequel "The Last of the Wild Ones," these stories typify the theme that your high school english teacher probably referred to pretentiously as man vs. machine.

In Zelazny's stories, computerized cars of the near future become infected with a radio-communicable virus that turns them "wild." Such cars "mono" their owners and strike off for the wild country. They eventually form "car herds" where the big cars fight for mastery and a harem of sports cars.

Noder Zerotime reports: Robert Rankin also steals Zelazny's idea for a scene near the end of The Most Amazing Man Who Ever Lived, and Ouroboros suggests that Stephen King's Maximum Overdrive is another candidate.