While replacing the Alaskan Way Viaduct will be a major project, it is important to note that Boston’s Central Artery/Tunnel Project (a.k.a. the "Big Dig") was substantially larger and more complex. Boston’s project was eight miles long with multiple tunnels and bridges, including a signature cable-stayed bridge over the Charles River. The Big Dig also included a disruptive cut-and-cover tunnel through downtown and two sets of immersed tubes under the Boston Harbor to the airport. The project was built while traffic was maintained through the construction zone and businesses stayed open with heavy equipment operating outside their doorsteps. This approach required extensive traffic management and mitigation.
For the viaduct's central waterfront section, there is an ongoing environmental process that is reviewing three alternatives - a bored tunnel, cut-and-cover tunnel and an elevated structure. If the bored tunnel alternative moves forward, the proposed SR 99 bored tunnel would be less than half the length of what was constructed in Boston. By boring under First Avenue, which is the proposed route, we would also minimize traffic disruptions and impacts to the waterfront and downtown.
| |
South end viaduct replacement and bored tunnel alternative |
Boston's "Big Dig" Project |
| Length of tunnels* |
2 miles |
5 miles |
| Tunnel lane miles |
8 miles |
80 miles |
| Total project length |
3 miles |
8 miles |
| Total lane miles |
14 miles |
More than
160 miles |
* Big Dig tunnels included cut-and-cover, immersed tubes, jacked tunnel and other special tunneling methods.
Why did the Big Dig have cost and schedule overruns?
The major reasons for cost overruns on the Big Dig were inflation, schedule delays and added scope. The original cost estimate for the Big Dig was in current year dollars and did not account for project changes, mitigation, environmental requirements, inflation, and appropriate allowances for risk and escalation.
The Big Dig also experienced management changes throughout the life of the project; this led to a lack of consistent leadership. As a result, the project was delivered over budget and years behind schedule.
How will lessons from the Big Dig be addressed in Seattle?
WSDOT uses the rigorous CEVP® process for all state projects exceeding $100 million to ensure costs are complete, reasonable, defendable and appropriately represent risk and uncertainties. Since adopting the CEVP process, WSDOT has had an excellent record of delivering projects on time and at or below budget, and the process is being adopted as a standard by other state and federal agencies. For instance, of the 185 Nickel and Transportation Partnership projects completed to date, WSDOT completed 90 percent early or on-time and 88 percent under or on-budget.
Additionally, to implement the bored tunnel recommendation, the governor, county executive and mayor signed a letter of agreement (pdf 459 kb) that assigns projects to each jurisdiction. Each jurisdiction has a specific leadership role and will be responsible for their own projects’ management, environmental work, design and construction.
Governor Gregoire is the project authority, and WSDOT is a strong owner with proven management and technical ability. WSDOT will remain a strong owner during the life of the project, assisted by eminent private-sector engineers and contractors, accountable to the public, governor and legislature.
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