My wife is currently on contract to Microsoft, and works in a building right on NE 40th at the overpass, so I see that mess a lot. The Seattle Times had a map showing the proposed overpass. It connects a road inside of Microsoft Campus on one side of the highway to a road inside campus on the other side by making an angled crossing of Highway 520. According to the story, the road on the overpass will be two lanes, and the overpass will also have foot and bicycle lanes, as well as trees. Knowing Microsoft, the edges will probably be grassed between the trees, so it seem like you never leave their wooded maze of parking lots and connecting streets.
If the road was being built to take traffic from Redmond in general, it would probably be designed without the foliage and have only a sidewalk, like NE 40th. People don't drive through Microsoft as a shortcut, because it's not designed for that sort of traffic, so the only users of the new overpass will be people going between buildings within Microsoft. There are a lot of people working there, so being able to do this without exiting onto normal Redmond roads and crossing at NE 40th will reduce a lot of congestion on that road. The benefits touted for Redmond are a side-effect, and presented as they are for PR reasons. The design of the overpass is to look like it is a part of their campus. The direct benefits will be to Microsoft. I therefore agree that Microsoft should foot the entire bill.
Please note that this project is being brought to light fast on the heels of the 10% pay cuts that were forced on the a- contract employees, so seeing how much money Microsoft will be paying for this fancy overpass, while cutting the wages of people who make their products possible, is especially galling. (The contractors affected by this have started discussing strategy at a website created by one of them, http://www.msratecuts.org/.)
Also, the a- folks who are being moved into at least one of the new buildings this week are going to be working in an even smaller space that they were in. Each contractor gets a 4-foot table and a single shelf. Some of these people have been working with multiple PCs and multiple monitors in order to do their jobs. The new space has been dubbed a slum by some of those who have already seen it.
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Read about how a fictional job action might go down at http://klurgsheld.wordpress.com/2009/03/12/short-story-contractor-uprising/.