While the total cost of the viaduct replacement program is estimated at $4.2 billion, we estimate the proposed SR 99 bored tunnel itself, including vent buildings and north and south portals, would cost $1.96 billion.
| Proposed SR 99 bored tunnel |
2010 Cost Estimate
(millions)* |
| Construction (including construction management) |
$1,224 |
| Right of way |
$152 |
| Preliminary and final design |
$169 |
| Risk and inflation |
$415 |
| Total |
$1,960 |
| * Estimates reflect year of expenditure dollars. |
|
The new estimate is based on an extensive cost and risk assessment to identify the tunnel’s probable cost and schedule. Since our original January 2009 estimate, the program team has developed more advanced engineering plans for the tunnel, and crews conducted more than 70 geotechnical borings for soil samples and approximately 300 surveys of buildings and other structures along the tunnel route. We also benefitted from the involvement of a number of highly-qualified independent subject-matter experts and cost estimators experienced in tunnels, underground construction and megaproject delivery.
The higher level of engineering detail and independent reviews helped our design teams and project management identify key cost and risk drivers – such as right of way needs, potential ground settlement and construction sequencing issues – which could lead to cost increases. Once we better understood the risks, we took steps to manage or reduce them through value engineering and design changes.
This method of cost estimating is consistent with WSDOT’s Cost Estimate Validation Process (CEVP®). A key difference between conventional estimating and CEVP® is the combination of a base cost (if all goes as planned) plus a risk cost (if risk events occur) and opportunity costs (if events go better than anticipated). This shows the effect of risks, if they occur, and helps us develop risk management plans to better control costs.
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