Federal jet traffic forecasts used to justify an $8.7 billion O'Hare International Airport expansion, which sent noise complaints soaring, have fallen so short of projections that O'Hare won't need more runways until at least 2034, experts hired by the Suburban O'Hare Commission contended Wednesday. Rather than adding and expanding even more runways, as planned, O'Hare should add 15 to 20 more gates to reduce congestion on the ground, experts said in one of a series of reports released to suburban mayors.