The 520 bridge, also called the Evergreen Point Floating Bridge, runs East from Seattle to Medina across Lake Washington.
Design of the bridge[]
The bridge is a floating or pontoon bridge, supported by floating barges. It is the longest floating bridge in existence.
Dangerous flaws[]
The bridge was poorly designed, with hollow, multi-section towers, which are prone to collapse during an earthquake. Solid, single section towers are much stronger but are more expensive to build.
At its ends, the bridge is tethered by cables; if one of these cables snaps, such as during a windstorm, the bridge could float away from the shore and sink.
Since its initial construction, the state has compounded the design flaws, adding additional "features" to the bridge which make it heavier, placing greater load on its deck and support cables.
Replacement plans[]
Due to design flaws, state wants to replace the 520 bridge. Plans are controversial because they call for several reasons.
General Tolling[]
Part of the replacement plan is variable rate toll, which ranges between $1.80 and $3.50 during peak congestion. Between midnight and 5am, the bridge will be free.
Expansion of tolls to I-90[]
With a toll on 520, some drivers will divert to I-90 to cross Lake Washington. If this level is high enough, congestion on I-90 will increase. Current estimates are that the average speed on 520 will increase by 20 miles per hour while, while average speeds on I-90 will fall between 5-10 miles per hour. If congestion becomes too severe, tolling on I-90 is likely. There are no plans by WSDOT currently for tolling of general purpose lanes on other highways in the region.
Undercapacity[]
Critics argue that the new bridge will not add any general use lanes and that bhe current bridge is often congested due to minor breakdowns. The new design will, however, include shoulders in both directions and add HOV lanes for buses and carpoolers.
Slow timeline[]
Tolling will begin on December 29th, 2011, but the new bridge is not scheduled for completion until 2018. Some percieve this being unjust.