Washingston State Department of Transportation has released the revised cost estimates for its project to improve SR 520 highway corridor. Costs range between $4.562 billion and $6.672 billion, depending on which design option is chosen for the western side of the scheme. Estimates in September 2006 had been in the range of US$2.79 to US$4.38 billion.
It cites five key factors that have increased the costs:
- increases in construction material costs;
- updated geotechnical information resulting in a complex design for the pontoon construction site.
- increases in quantities of materials as a result of additional design information;
- new regulations affecting wetland mitigation and stormwater treatment;
- provision for future high capacity transit. Revised costs have also been released for a range of surface, elevated and below ground options for the Seattle's Alaskan Way Viaduct project, putting the cost at between US$800 million and US$3.5 billion.
