What type of trees grow well in your area ? I would start with that list. If the county agent is no help call a couple nurseries and ask them that. Fast growth to shield the highway further limits the choices. How tall will the trees need to be to do that? If 20 feet will work you could also consider hedges. Another would be a series of trellises with vines like honeysuckle , jasmine or other vines provided they will grow well.