which as part of the retrofit program, was nearly completely replaced. Because of the active use of the bridge, Caltrans designed the project to allow the bridge to remain open to traffic. For economy, schedule efficiency and traffic impact mitigation, much of the repair work was fabricated off site and shipped to the bridge by barge. To reduce impacts to traffic the major work was performed at night. Caltrans kept two lanes of traffic moving in each direction during daylight hours, then reduced that flow to a single lane in each direction at night. Thus, one trestle was completely closed, and the other trestle had two-way traffic. The concrete segments of the trestle were precast in Petaluma and barged to the site. At monthly intervals, tugs positioned barges with one or two , 500-ton pre-cast concrete roadway segments, which a 900-ton barge-mounted crane lifted into place. Earlier, either two or four of the corroded, concrete segments of the old roadway were removed by crane. Then, a pile driver moved into position and drove new piles. After the new concrete road segment was in place, steel plates were used to temporarily fill the gaps, and the roadway was ready for morning traffic. At times, construction backed up traffic to Highway 101 into central San Rafael. The completion of this retrofit, on September 22, 2005 was celebrated as a success despite the many challenges, including the deaths of two workers. The retrofit was originally estimated by Caltrans engineers at , but Caltrans adjusted the estimate to in 2000 during the bidding process. While most of the resulting bids were close to , the low bid came in at from the Tutor-Saliba/Koch/Tidewater Joint Venture. Caltrans revised their estimate to in May 2001 when more funds were appropriated for California's Toll Bridge Seismic Retrofit Program in Assembly Bill 1171. The cost was again adjusted during an August 2004 review by Caltrans, this time to . The final cost of the retrofit, however, was $778 million, or $136 million below this August 2004 estimate. Third lanes In both directions, the bridge is wide enough to accommodate three lanes of traffic. Currently the third lane on the lower deck is used as a right-hand shoulder or a "breakdown lane" and is marked along the bridge with the signs "Emergency Parking Only". The third lane on the upper deck is a separated bicycle and pedestrian path. In