NEW YORK (CNNMoney.com) -- Soaring gas prices are causing many Americans to change their summer travel plans, according to a study released Tuesday.

One-third of American families say they've scaled back their summer plans, according to a July survey of 5,000 U.S. households by the Conference Board.

The survey was conducted before the news of the alleged terrorist plot in London.

Of those changing plans, 63 percent said they'd stay closer to home, while 26 percent said they've postponed or shortened their vacations this year because of gas prices.

"These survey results show that while most Americans haven't changed their vacation plans because of rising gas prices, a substantial proportion - one in three - have been compelled to alter vacation activities," said the Conference Board in a press release.

"Looking ahead, the combination of high gas prices and possible fallout from the recent terrorist threat could further change Americans' travel plans."

Only one-fifth of respondents said gas prices had affected their commute to work. Of those, 20 percent said they've increased work from home, 16 percent said they are car-pooling, and 10 percent are now using public transportation.

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