WSDOT has released an updated cost estimate and tolling study for the Alaskan Way Viaduct replacement. This report, requested by the Legislature, shows that the cost estimate to replace the viaduct remains within its $3.1 billion budget, and that it is feasible to generate $400 million in toll funding for the replacement.

Updated cost estimate shows viaduct replacement remains within budget
Last year, when the legislature endorsed a bored tunnel as its preferred option for replacing the Alaskan Way Viaduct, they directed WSDOT to provide updated cost estimates for the viaduct replacement, including the proposed bored tunnel. After extensive cost and risk workshops, value engineering and design changes, we released the updated estimate this week.

WSDOT determined that the cost estimate to replace the viaduct remains within the $3.1 billion replacement budget, which includes $2.4 billion raised from existing state and federal sources and no more than $400 million raised from tolling the proposed bored tunnel. An additional $300 million is committed from the Port of Seattle.

The estimated cost for the bored tunnel increased by $60 million, to $1.96 billion; this increase, however, was offset by savings elsewhere, including design improvements for the south end viaduct replacement. Changes made to the proposed tunnel’s design in December, which included new north and south portal locations; resulting in a lengthening of the tunnel, with an overall increase of 640 feet.

These changes also addressed significant risks identified during our estimating process. For example, we moved the south end of the tunnel away from Pioneer Square to reduce the impact to this historic neighborhood and also reduce the potential need to reinforce older structures during construction. A better understanding of these risks gives us opportunities early in the project to manage or reduce them, and thus keep a tight rein on costs.

New study shows tolls could help fund proposed bored tunnel
As WSDOT updated the viaduct replacement’s cost estimate, the legislature also asked them to determine the potential for tolls to contribute to construction funding. They examined five toll scenarios, with low, medium and high toll rates, that would toll the proposed bored tunnel and, potentially, the north and south SR 99 segments that would lead to it. Their study showed that it is feasible to toll only the tunnel at a medium toll rate and generate $400 million to fill the gap in funding for the viaduct replacement.

If a toll is charged to use the tunnel, traffic model analysis shows that some traffic would divert to local streets and I-5, mostly during the midday, evening and weekend times when these routes are able to absorb additional trips. Because there is capacity during those off-peak times, travel times would stay the same or increase by two to four minutes. Tolling the proposed bored tunnel would encourage longer through trips and discourage shorter, more localized trips on SR 99.

This fall WSDOT will release a second Supplemental Draft Environmental Impact Statement for the viaduct replacement. The document will focus on the bored tunnel alternative and will look at how the transportation system functions, including the potential effects of tolling.