It's now become a familiar theme: The ad economy overall is suffering but out-of-home advertising and internet spending are sailing through this ad downturn largely unscathed.

The latest support for this scenario comes from ZenithOptimedia Worldwide, whose most recent forecast for U.S. spending has out-of-home spending growing by 11.2 percent this year, to $7.83 billion.

Next year it expects it to grow at a similar pace, 11.3 percent, to $8.71 billion, and in 2010 it will grow another 11.5 percent, to $9.72 billion.

That's against 3.7 percent growth this year for the entire U.S. ad economy, which is down from the 4.1 percent growth ZenithOptimedia forecast back in December. It's forecasting even slower growth in 2009 and 2010, by 2.1 percent and 2.2 percent.

ZenithOptimedia is forecasting that worldwide out-of-home spending will grow 9.4 percent this year, 8.0 percent in 2009, and 8.3 percent in 2010.

ZenithOptimedia senior publications executive Anne Austin defines out-of-home as including all outdoor advertising, from billboards to bus shelters and other forms of alternative media.

Just last month, the Outdoor Advertising Association of America reported that 2007 OOH spending had risen 7 percent over 2006, to $7.28 billion.