As with all traffic mitigations, the flyover is a stopgap measure to temporarily reduce current inconveniences. This case is more useless than most because it will just move the current bottleneck literally down the road. And it will probably be completed after Napa Pipe adds a thousand housing units, 200,000sf of industrial/retail space, a hotel and nursing home and, oh yes, a Costco. And after 500 housing units at Tulocay Village, the county jail, and 1250 units and a town center at Watson Ranch. All are a short drive from the flyover. And of course it will have to handle the hundreds of thousands of tourists that all of the as-yet-unbuilt vanity event centers are expecting to enable their unprofitable wineries to survive.
And of course if by some magic traffic mitigations worked to relieve congestion, that just greases the skids for more development.
The problem that the county should be considering is how to reduce traffic, not how to make a bad thing more bearable thus encouraging more bad things. Traffic congestion is a consequence of urban development, and the best way, really the only way, to ease traffic congestion is to stop urbanizing. As long as urbanization continues the traffic mitigations will never catch up to the impacts and everything will be as congested as before. The real best way to reduce traffic congestion not just to stop urbanizing but is to reverse urbanization - to begin engaging in ruralization.
Is it possible to ruralize in this place at this time? Well Napa has one of the most expensive legal crops in the world. As Andy Beckstoffer said in a recent article: "Never in the history of mankind has agriculture withstood urban growth long-term, but here we have the best chance."
All the politicians say they want to preserve the agriculture that is the golden goose of the Napa Valley. In the meantime the vineyards are being filled up with building projects. It is time for our politicians to jettison the idea of smart growth (which more recently they've actually replaced with dumb growth) and instead begin looking at ideas that might reverse growth. Maybe then we wouldn't be so anxious to get out of town.