The Casco Bay Bridge will open more frequently over the next several weeks, halting traffic for as along as seven minutes each time. The purpose of the openings is for testing the bridge and training the staff of the new private bridge operator. The training period will begin Thursday and last through March 5, according to the city of Portland. The bridge connecting Portland and South Portland carries around 32,000 vehicles a day. During the training period, the bridge will not be opened during its busiest traffic times — from 7 to 9 a.m.