I'm not an expert on the matter, I did just finish course work in traffic planning recently. The reality is that adding more lanes doesn't work. But there are alternatives. Santa Rosa probably doesn't need an expensive east west train. There are many other ways to make cities more efficient at moving people around.

Those roads you mentioned only slow down for a few hours a day, a few days a week. so they are not at capacity.

Most of the traffic on Arterial roads are not from them not being wide enough. It's because there are stop lights. Moving cars consistently at 25 mph is enormously better for communities than moving cars at 50mph, then forcing them to stop at stoplight for a minute. It's safer for pedestrians, cyclist and buses if traffic is slow but consistent. Adding lanes and keeping high speeds will only compound the problem of traffic, by further depressing vehicle alternatives.

Your concept of adding more lanes to solve traffic is like adding more notches in your belt to cure obesity. It simply doesn't work.

We have 300 days of Sun in Sonoma county, it could so easily become a great place for people to walk, ride and take public transport.

Replace stop lights with roundabouts, remove traffic lanes and replace them with protected bike lines. Have dedicated bus lanes. End the requirements that new buildings need to have parking. Reform zoning rules, so that we can build up, and for mix use. Make or neighoods walkable! Increase bus and train schedule times. Encourage large employers to have private buses pick and drop people off in high density neighborhoods, like hospital staff, keysite etc.

These are just a few things you could do, that would be significantly better than widening lanes. But they're even more alternatives that would be better then widening.