Planning to drive for the holidays or a winter vacation? A new transportation study by the Union of Concerned Scientists contains a wealth of data about the greenest ways to go. Not surprisingly, a bus is often the winner. But in some cases -- such as when a person is driving a long distance solo -- flying is actually better.

One interesting element: A family of four choosing a Chevrolet Suburban, which the UCS says is one of the most inefficient SUVs on the road, over a Toyota Prius will more than triple their carbon pollution for the same trip. The report, titled "Getting There Greener," has lots of other data about travel on planes, trains and buses. See it here:

But what if the SUV is the only car you own? The UCS analyzed the data, and found that factoring in the cost of gas and other expenses, it's actually cheaper to rent a hybrid car. (Although they only define the rental rates as "competitive," and they factor in gas at $3.50 a gallon.) The emissions for a 500-mile vacation drop from 1,061 pounds of carbon to 281.

Meanwhile, Enterprise Rent-A-Car has announced it is designating five Philadelphia area rental locations – including Philadelphia International Airport – as "hybrid branches."  The other four locations are:

36 S. 19th Street in Philadelphia
123 S. 12th Street in Philadelphia
725 E. Market Street in West Chester
3201 U.S. RT 1-Brunswick Park in Lawrenceville, NJ

Nationwide, Enterprise is designating 80 branches and and adding nearly 5,000 hybrids to their fleets. They include the Prius, Nissan Altima, Toyota Camry and Ford Escape. Local rental rates start at $59.99 per day but will vary according to market conditions, according to a company statement.

"Customers who want an environmentally friendly or fuel-efficient vehicle often ask about hybrids," said Bobby Keyes, vice president and general manager for Enterprise Rent-A-Car in Philadelphia. "More than doubling the number of hybrids in our fleet means they have more choices than ever."

Customers can reserve a hybrid at any of the five designated Philadelphia "hybrid branch" rental locations online at www.enterprise.com or by calling 1-800-RENT-A-CAR.