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Wednesday, November 2, 2016

DDI: Diverging Diamond Interchange


Diverging Diamond Interchange comes to Washington State

Sometimes it seems like highway designers are running wild. The roadways may not be any wider, but the space surrounding them is growing. What used to take a couple of acres now takes 10 or 20 or 30. Problem is that the highway departments are charged with making roads safer, but we are still operating our motor vehicles with version 1.0 humans, so designers are responding with larger run-out areas. Being as medical care for even minor injuries can run into tens of thousands of dollars, it makes a certain amount of sense to set aside these wide open areas around these intersections. Sliding through the grass off the side of the road may scuff the paint on your car, but you are unlikely to be injured.
     I see one problem with this DDI design and that is that you can only have traffic flowing on the overpass in one direction at a time. This would only be a problem if most of your traffic was simply crossing the Interstate. If most of it is either getting on or off the Interstate, then it might work okay, though I suspect traffic light wait times are going to be longer. I guess we just have to have faith that the traffic engineers know what they are doing.

Jackson School Road Roundabout Plan
Meanwhile, back at the ranch, Washington County has started construction on a roundabout to deal with, you guessed it, increased traffic coming from NW Scotch Church Road. Seems all the jobs are in Portland, but nobody wants to pay Portland rents, so they live out in the boonies and commute. Going this way is about 3/4 of a mile shorter than taking Glencoe Road north to North Plains. A simpler solution would have been to just close Scotch Church Road, but that would be moving backwards I suppose, and we can't be having that.

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