Last week, I wrote about why Millennials might shun the cars that their parents loved and relied on. They simply have more alternatives, from bikeshare systems to better public transit to Uber and Lyft. They have less money to spend on car payments, thanks to rising students loans and the big-city cost of housing. And they're simply less interested in ownership of all kinds of things.

But Tuesday, at The Washington Post's America Answers conference on transportation, former transportation secretary Andrew Card, who was President George W. Bush's chief of staff, suggested another fascinating cultural explanation for the Millennial shift on automobiles that I hadn't considered:

"My generation loved the muscle cars growing up, and that was because of cheap gas and the excitement," Card says. "But the automobile is also a refuge, it’s a place where you can be alone and vent, where you can have conversations that you wouldn’t have in public. And it’s a freedom machine. You can drive where you want to, when you want to, say the things you want to without accountability. It’s a safe place to be.

"We could have a private relationship with ourselves in the car," he added.

In the era of oversharing, digital everything, constant connection, smart phones, Twitter and FourSquare, it's quite possible that Millennials are simply less interested in that refuge — the quiet, the solitude, the detachment — offered by privately owned vehicles. I suspect that this is true in a practical sense: You can't scroll through your smart phone from behind the wheel of a car. To drive is to literally be detached from devices. Driving is the one activity that can't — or shouldn't — easily be multitasked.

Card, though, is also talking about a broader cultural shift here.

"There is a difference today in the definition of privacy that is not what it used to be," he says. "I think people today have an intimate relationship that is digital with almost everyone."

Perhaps young people less concerned with private time in their own private spaces simply don't value one of the qualities that made cars alluring to their parents.