Demolition of the old Carquinez Bridge will cost more than three times as much as the state estimated, the latest example of a huge Caltrans cost overrun on a Bay Area bridge project. A committee of the Bay Area Toll Authority reluctantly agreed Wednesday to allot $49.7 million for the demolition and removal of the original span of the bridge, a job that state engineers had said would cost $16 million. The 1927-vintage span, considered too fragile for seismic strengthening, was replaced in November 2003 by the Al Zampa Bridge.