I am also in Central California zone 9. Around here many people plant Oleander Sister Agnes. I don't especially like Oleander but I have to admit it is perfectly used as a screen. It also is a shrub that looks better from a distance. How close is the road to your house?
I know you want a tree but these will fill in until your tree is large enough to fill out.

For trees, the Valley Oak. It is their native home.

If you really want to do it right, for a sound barrier what you really need is a soil berm with a hedges of shrubs planted on the top of it. A soil berm is the most effective way of absorbing traffic noise and could add long-term value to your property.

If you would like to provide shelter for birds (which will then keep your property mostly free of insect pests) consider a screen of native shrubs.

Here is a link that might be useful: Valley Oak

The oleander would provide a visual screen but do nothing to stop the traffic noise. We had a similar noise/ visual problem here with the road winding around us. The folks planted 150 oleanders along the road which stopped us from seeing the traffic but we could hear and smell it. Our garden always smelled of diesel exhaust. After 50 years the county moved the road to get rid of the sharp turns and many deaths from accidents. The house was built of concrete and double pane windows did a good job of blocking the noise inside, as long as you could keep the windows closed. Al