Call your local governing body. Ask about the code requirements for backyard fencing for your address. Unless you live in a rural area, your municipality likely has a height limit for fences and yard walls.
Add a wall of masonry or a solid fence to your backyard. Make it as tall as your zoning laws will allow, and do not include decorative gaps in the structure or along the bottom. You might consider a two-paneled fence with a noise-absorbing material in the middle.
Do some planting around your fence or wall. Evergreen and deciduous trees enhance the noise-reducing capacity of the structure and can make it look more attractive. For additional noise reduction, plant vines for a thick textured covering on your fence or wall.
Plant evergreens instead of installing a fence or wall. This is less effective, but will decrease some road noise if you do not choose to have a structure built in your yard. Plant at least two rows of tall evergreen trees close to the road, along with a row of evergreen shrubs, as recommended by FunctionalGardens.com. Add smaller evergreen shrubs and other plantings underneath.
Buy a water fountain or create a small waterfall area in your yard to act as white noise and mask the sounds of traffic. Place this feature close to an area where you prefer to socialize, or where you'd like a sense of peace and quiet. You might need more than one water feature to effectively decrease road noise.