Diagrams used by the Washington State Department of Transportation seeking bids to rebuild the 520 bridge show a span far wider than represented in documents released publicly for an impact study. Previous plans for replacing the aging four-lane bridge, released in a January environmental impacts study (.pdf), have shown a bridge with six lanes—with four used for mixed automobile traffic and two lanes reserved for carpools (or HOV lanes). It would be 115 feet wide.
In a document released last month, the state's transportation department writes (.pdf): "Within these limits, SR 520 would be six lanes." This reflects the state laws authorizing the bridge: "The state route number 520 bridge replacement and HOV project shall be designed to provide six total lanes, with two lanes that are for transit and high-occupancy vehicle travel, and four general purpose lanes," the RCW states.
Here is a cross section of that design:

But documents (.pdf) released by WSDOT to gather construction bids in September show that the bridge would be designed to expand to a much larger bridge. In that case, light rail would be added to the six vehicles lanes by widening the bridge (click image to enlarge).
Here is a cross section of the bridge depicted in bidding documents:
"We have not found what is depicted here anywhere, and it is in direct conflict with the depictions you do see publicly," says Fran Conley, head of the Coalition for a Sustainable 520, which advocates that the two new lanes for the bridge be outfitted with light-rail tracks from the outset.
The diagram shows the bridge, as submitted to potential contractors, could be built out to hold at least six lanes for cars, two lanes for light rail, and possible two more lanes, Conley says. "The very broad shoulders mean that they could just be re-striped to allow additional lanes, so we could be looking at ten lanes," she says. "That is completely contrary to many verbal agreements with the citizens and mediation and other state sponsored forums."

Another law says that the state must, "minimize the total footprint and width of the bridge." This widened design depicts a bridge that is 140 feet wide, the equivalent of a 14-story building on its side (and 25 feet wider than shown previously), which is nearly 2.5 times wider than the 60-foot-wide existing bridge.
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