O’Hare Airport lost passenger traffic last year at a faster rate than any other major airport in the world. That’s according to a new report from an industry trade group.

Preliminary numbers from Airports Council International show O’Hare passenger traffic dropped 8.8 percent in 2009.

The Geneva, Switzerland-based group reports that O’Hare tumbled two spots, to No. 4, among the world’s busiest airports, trailing Atlanta, London and Beijing.

Joe Schweiterman is a transportation expert with the Chaddick Institute for Metropolitan Development at DePaul University.

SCHWEITERMAN: You know, it was a perfect storm for Chicago. We have the weak U.S. Aviation market, and the fact that we’re a two-hub operation at O’Hare … And that led to a drop that’s quite alarming.

He says Chicago’s Midway Airport is also sapping traffic from O’Hare, and that small regional carriers have begun flying direct to mid-sized cities, instead of transfering through big airports.

Schweiterman says the report also casts some doubt on the necessity of Chicago’s multi-billion dollar plan to expand the O’Hare.

A representative for the Chicago Department of Aviation, which oversees both O’Hare and Midway airports, says passenger traffic is cyclical, and expansion will move forward as planned.