Do you have a list of fast-growing trees that block traffic sounds?
You will most likely be looking for a conifer (evergreen) species to create a screen. Leland Cypress, Incense-cedar, or Arborvitae are some of the most common ones people use. There are some native conifers in your area, such as Shore pine, Western hemlock, Sitka spruce, or Western red-cedar that you could us, but they don't usually work as well for a 'hedge' type form.
Visit http://oregonstate.edu/dept/ldplants/ to find out more about these species.