That dead tree looks like Cedrus atlantica. To replant the same species is like getting more goats after the cougars have already found a source of their fav diet...goat meat.
I will suggest one of my favorite plants; Salix purpurea 'nana'. This shrub has mass fine branches with mass fine, 1" by 1/4" blue green leaves. The branches are flexible and they are a copper bronze color. This deciduous shrub is amazing all year round for a screen and sound barrier. Easy to prune in fact I had hedges of this plant that I transplanted 3 or 4 times and kept them at 3' high. They are wanting to be 30' high and 30' wide. Far more foliage and branching to absorb sound. FAST growth! Lightly heading will cause a denser plant. This shrub is one of the hardiest you can find. Gorgeous new growth, light green, and then the leaves get this blue green to die for. Super duper 'skeleton plant' for a landscape. Another quality is movement in the wind, similar to grasses.
I'd get another offset hedge going of this Blue Arctic Willow. Not just a straight line but two lines where plants are in equilateral triangles. If one dies it won't be noticed. Planted 3' apart. Will also stop dust.
This shrub is disease/insect problem free and so very adaptable to environmental conditions. Your healthy conifers will only add to your barrier. This will 'fill' in and when mature can replace any of your conifers that die. This shrub will also not be subject to whatever disease that might be compromising your conifers. Remember these shrubs grow to 30'by30'. Best if you head them while young to make more branching, to be thicker. Make room for them with a plant bed at least 15' wide and at least 10 feet from your conifers! In a few years you will never be able to see much less hear the traffic on that road.
Add a balanced fertilizer to the plant beds you make out of that lawn. I'd rent a sod cutter to make those beds as well as clean up the edges of your entire lawn. Use that sod turned upside down to beef up a plant bed adding at least 2 or 4" topsoil.
That grey is Senecio greyii in the foreground. Behind this wonderful shrub that well, isn't that professional but I love it and it is healthy is the blue arctic willow soft hedge. See how it is not in a straight line? I'll try to find pictures that show a hedge planted offset. This hedge is bluer later in the year. As you can see the hosta are just coming up because this is early spring in zone 5. Salix purpurea is good down to 1B! So much fun to hedge! Like cutting hair, take a big wad up and chop off. Well, not exactly that coarse but the fine branches are so easy to prune, and did I say they moved in the wind? Another dimension most don't think about.
If you look at your picture, a 5' shrub will completely block that view. This will do that for you both summer and winter and not be subject to whatever disease is going on for your conifers. Well, it is high resistance to the diseases you might have. We'll discuss that later. Need you to do some detective work with a scalpel