Nowhere is the adage "Time is money!" more prophetic than on the new Bay Bridge.

Engineers' cost estimates to replace the seismically shaky eastern half of the Bay Bridge have risen dramatically since February 1997, when then-Gov. Pete Wilson ordered it replaced rather than retrofitted.

In part, the projections grew because the bridge evolved from a no-frills crossing based on minimal design details, to a fully designed, single-tower self-anchored bridge with shoulders, lighting, architectural features, and a bicycle and pedestrian path.

Here's the evolution of changes that affected the project's total costs:

August 1997: Standard concrete viaduct with a cable-type suspension span but no bike lane or shoulders. (Cost $1.3 billion)

June 1998: Concrete skyway and single-tower self-anchored suspension span with shoulders, lighting, architectural features, and bicycle and pedestrian path, based on 30 percent design documents. (Cost $1.4 billion)

April 2001: Skyway fully designed and the plans for the suspension span at 65 percent. (Cost $2.6 billion)

August 2004: 100 percent designed and skyway under construction, but global steel prices skyrocket and post-911 climate drive up contractors' costs for bonding. Caltrans admits earlier budget lacked sufficient contingency. (Cost $5.1 billion)

July 2005: Legislature shifts bridge construction management to new three-member oversight panel consisting of the executive directors of the Metropolitan Transportation Commission, California Transportation Commission and Caltrans. (Cost $5.4 billion)

December 2007: Under new management and after the contract for the most expensive piece of the bridge (the self-anchored suspension segment) was awarded, the rate of escalation slows. (Cost $5.6 billion)

May 2013: Inflation and delays associated with the complexity of fabricating and installing the massive steel decks, coupled with broken steel anchor rods in seismic stabilizers, continue to push the cost projections up, although not at the earlier rate. (Cost $6.4 billion)

Source: Caltrans, Bay Area Toll Authority