“If you are driving on average in America this summer, you’ll save — according to Department of Energy figures — about $70.”

Sen. Hillary Clinton has urged a three-month gas tax holiday as a way of lightening the load on drivers this summer. The gas tax is 18.4 cents a gallon for gasoline — and even higher at 24.4 cents for diesel — so a cut could help consumers.

Clinton has said consumers will save $70 from the holiday. Sen. Barack Obama, who opposes the holiday as a political gimmick, says it will only save $28. Who’s right?

The Clinton campaign referred us to Energy Department numbers that show a family of four with two cars uses 1,519 gallons of gas a year. (The exact average is 2.3 vehicles per family.) Take a quarter of the 1,519 gallons to represent the three months of summer, and you would see a savings of $69.87 on gas taxes.

The number and the math are correct, and since driving tends to increase in the summer, it may be a little low.

Barack Obama, on the other hand, arrived at $28 by calculating per-vehicle savings.

We examined his statement in depth and rated it Mostly True.

We’ll note here that many economists think it will be even less than that because the entire tax cut won’t be reflected in the price at the pump. Certainly, oil companies and retailers could decide to keep part of the money for themselves. But a cut in prices will also stimulate demand by making people more willing to use their vehicles. Increased demand is likely to send prices up, eating away at the 18.4 cents a gallon.

The problem we have with Clinton’s number is that she left out the reference to a family of four when she talked about it on

This Week with George Stephanopoulos

on May 4, 2008.

“But if you are driving on average in America this summer, you’ll save — according to Department of Energy figures — about $70,” she said.

And it wasn’t the only time she left out the family-of-four qualifier. We found Clinton made the following statements the day after the appearance on

This Week.

“By our numbers, the Department of Energy suggests that it would save consumers on average $70,” she said on Fox News’

Fox & Friends.

To Katie Couric, on the

CBS Evening News

, Clinton said she is “trying to give folks, on average it would be $70. For a lot of people it would be a lot more.”

“So here’s what I believe, is let’s give you a break this summer. For the average person it would be about $70,” she said at a campaign event in Greenville, N.C.

We’ll say it again: You only get to $70 by calculating the savings for a family of four, which has two vehicles. Leaving out that qualifier makes a big difference. In fact, if $70 is the savings for a family of four with at least two vehicles, it seems likely that the average savings for an individual would be closer to half of $70 than the $70 Clinton claims. We rate her statement False.