http://www.radioworld.com/pages/s.0121/t.14665.html

"At 10% IBOC transmission power, most stations would gain covered
population, approximately equaling analog indoor and portable and
exceeding auto. However, they’d pay the price from digital interference
to their analog signals. At this power level, stations would lose an
average of 26% of their FM auto population coverage because of IBOC
interference, the lab concludes. “Interference would affect some
stations severely,” 41% could lose a third or more of their covered
population and 18% would lose more than half of their population."