The I-5 and Marvin Road overpass, due for a makeover, in Lacey will be the state of Washington’s first “Diverging Diamond Interchange.”
Here's how it works:
The overpass will be expanded to six lanes, three each direction to handle the flow.
Then when construction is finished, traffic will swap sides just before entering the overpass. In other words, cars will be traveling down the left lanes - like in England.
That allows drivers to enter the I-5 onramp without stopping, no left-turn light needed.
Drivers going straight across the overpass will then swap back over to the right lanes.
“It’s a proven and innovative way to effectively move traffic and people through an interchange,” said Washington Department of Transportation Project Engineer Kim Mueller.
Mueller said the system should reduce gridlock and improve safety on the overpass.
Started in Missouri in 2009, Mueller said most states have implemented the diamond systems.
Work is scheduled to start in late summer of 2018. Completion is expected in 2020. The project is budgeted to cost $72 million.
The diamond system is the leading proposal for a future interchange upgrade at I-90 and Highway 18.
