Fewer young drivers are getting a whiff of that new-car smell.

The share of new cars bought by 18-34 year olds dropped 30 percent throughout the last five years, according to

But the reason for the big decline is up for debate.

Some point a finger at the economy.

Young adults face high levels of unemployment -- with many giving up the job search altogether. So, young drivers may opt for a used car, or borrow mom and dad's keys, until the job market comes back to life.

But others say the drop may show a shift in priorities.

As urban populations swell, young adults may be swapping their wheels for a bus ticket or a subway pass. Companies like Zipcar provide rental cars in a pinch.

Social media also has a role to play.

Cars used to mean freedom for young drivers, but with the rise of cell phones and the internet, young adults interact without ever leaving the house. So, getting behind the wheel is less important.

Meanwhile, car companies hold out hope that as these drivers get older, new cars will become a must-buy.