In 2011 the Ford motor company was interviewed for this Gartner group analysis:

In a survey to be published later this year, Gartner found that 46 percent of people 18 to 24 would choose access to the Internet over access to their own car. Only 15 percent of the baby boom generation would say that, the survey found. “The iPhone is the Ford Mustang of today,”

I dug up this article since I was reading online a more recent article in the “TheWorldPost”.  They, mention the economy, college and lack of marriage for some of the decline but most of it is as follows:

“The larger declines experienced by younger age groups reflect patterns specific to Millennials and younger members of Gen X and could be caused by changing attitudes toward mobility among younger Americans as well as differential substitution of online for physical interaction among digital natives,” she writes.

Basically: the smartphone is the new car.

With the google car running around these days who knows what transportation will look like in the next five years.