The vast majority of road noise (bad/loud exhaust not withstanding) comes from the tire noise. As a result, low growing dense bush/shrub is the most efficient method of reducing road noise. Trees are not the best.

Arborvitae, Thuja occidentalis, is the Standard Poodle of American trees. Most dog folks know that Standard Poodles were once, and can be, excellent hunting dogs, but people bred them and clipped them to look stupid. Arborvitae likewise: useful but made to look stupid. Also called Northern White-Cedar, their uses include canoe-making, fences, shingles, a high Vitamin C tea, and medicine.

In the wild they have a fuller profile than the hedge trees that you see pictures of. If you can keep the deer from stripping them (they are deer candy; try Jack’s method) they could be a terrific contributor to a mixed conifer and shrub planting, staggered like Jack describes. For anyone who lives in the right environment where they can thrive, they make a great homesteader’s tree, with the privacy function a secondary benefit.

On cardboard, grocery stores recycle cardboard. They have big balers they use and make about $300+ per bale. If you talk to a manager at the store, they will probably be more than happy to allow you to take that in for you.

Arborvitae are the gold standard for sound barriers. I think Jack is underestimating their density. It’s like a christmas tree that’s been sun through a tree bailer. If properly pruned, you can’t stick your arm through it to reach the trunk that’s just 12″ deep in the tree. The insulative properties make it ideal winter bird habitat as well. But it’s extremely good at cutting noise and wind (and creating a barrier for road trash).

The Arbor Day foundation has them for under $4. They should be spaced at 20″, so 60 trees per 100′, should run you about $200.

If you want to double their effectiveness, head to the car auctions and find yourself an old white or black Ford Crown Victoria or an Interceptor, and park it so just the headlights are sticking out from the bushes facing the road. Watch all the idiots slow down as they are conditioned to believe it’s a speed trap. It’s like a scarecrow for bad drivers. According to studies, at highway speeds, a 5 mile an hour reduction on a busy road can cut noise by as much as 4dB.

You might even go as far as to “report” a speed trap or camera 1000′ before and after your property on Waze (the most commonly used navigation app by commercial drivers). It warns them well in advance to slow down, and when the big trucks slow down, everyone does by necessity.

I’m going to disagree with the forest advice for noise control. If done too densely, the canopy will eventually fill in and shade the ground, leaving lots of air space between the canopy and the ground, stifling shrubs. If you’ve ever walked through a forest, you know the echo of a deer stepping on a twig that can be heard clearly and loudly from 100 yards away. Forests are echo chambers.

I think Jack is more recommending a Savannah style planting with layered shrubs and trees of different heights, spaced out such that light can hit everything. That’s ideal, but the term “forest” was used, and that may conjure the wrong image and lead to tree-dominated plan which will work in the short term, but 15-20 years from now could make things worse.

Also, avoid fruiting trees in this case. You’re on a highway, non sense in baiting deer near a busy road. Best case scenario, you’ll have to remove a few rotting carcasses each year. Worst case, it may cause an accident on the road and hurt someone. Keep any fruiting trees well away from the road (200′ at least). Maybe even cut a path laid with clover and bordered by persimmon for deer that get into the property to follow safely away from the road, letting out on the opposite side of the property.