In other words are the spread of branches on either side of the tree the same. IMHO they are not. The branches into the road are making a conscious effort to reach and touch the branches of the tree on the other side of the road. This is the impression i get while driving down a tree lined road. Especially in England where the roads are narrow enough for the effort by the tree to be worthwhile.
Trees will grow in the direction of available sunlight. Any clearing in an otherwise forested area will have the trees around the edges adding growth in the direction of the clearing. There is no consciousness involved, it’s purely hard-wired programming.
Leaving aside any consideration of consciousness or intent, the question is probably more accurately “Does the growth pattern of trees have a bias to grow more strongly over the roadway than in the other directions?” Which implies an environment-focused question: “Are there environmental factors that cause trees to grow asymmetrically in proximity to a roadway?”
My no-evidence guess is “no”. Maybe someone knowledgeable in the field (hah) may have a more definitive answer.
Try driving on the other side of the trees, 50 feet off of the road; take a look up and see what those branches look like. In fact, you should take a picture from that location and compare it to 1/2 of a picture you take when looking up from the centerline of the road; my guess is they’ll look the same.
It’s pretty clear that plants grow “toward” sunlight when possible. As Stana Claus said, they will add growth in whatever direction there is clear access to more light. I used to grow herbs and peppers and things in an herb window in my house: I had to frequently rotate the plants to keep them from getting lopsided and falling over (they would add more growth and lean “out” toward the window).
So if you go through a stand of trees and cut a road through it, the remaining trees will add growth in the newly clear area above the road. If there’s less light on the other side of the tree, due to buildings, or other trees, yes, I would say the growth might be “biased” in the direction of “over the roadway.”
That said, they’re probably still pretty symmetrical, trees mostly always spread toward the top, so of course the spread will reach across anything under them (the road).
Sadly, the growth is normally nowhere near symmetrical. There is no (or limited) value to the tree to spend the energy on growth that doesn’t receive sufficient sunlight. So the shaded side grows sparsely, while the side over the road or other clearing adds as much growth as it can. This is why you end up with trees toppling over into the roadways after heavy snows and/or ice storms.
Sure it’s not how the trees were trimmed by the municipalities? Often down tree lined roads they will trim trees up to a certain height so tall trucks can pass through unobstructed. The tallest branches are left alone to overhang the street. Over time the street will have a tunnel like affect.
Certainly in an urban, or possibly even suburban, area where the trees aren’t surrounded by other trees except for where the road is, the situation is changed substantially. I’m talking about highways or roads that are cut through forested areas and create an opening for the trees along the edges to grow into. Those trees will become quite lopsided over time.
I live in a mobile home park that was placed in an old growth black walnut grove and all the trees on both sides of the road have a very distinct curviture out over the road and all the trees away from the road grow straight up. The road was carved through here in the mid 1960s. I leave it to others to draw any conclusions, this is just what I see daily outside my door.
You really have a few things going on at the same time. Apical dominance is basically how much control the main stem of the tree has over the branches. Conifers have strong apical dominance and will generally grow symmetrically given roughly equal shade conditions. Deciduous tree generally have less apical dominance and have less control over their branches. If one branch is getting more sunlight it will turn up and become the new main bole of the tree.
The second issue is self-pruning, conifer branches tend to persist longer then deciduous branches in limited light conditions and shade tolerant conifers can have branches that persist along time.
If you cut a road through a forest you are exposing one half of the tree to more sunlight while the other side is still shaded. With a conifer this might not make much of a difference for many years but it will eventually be lopsided. With a deciduous tree with weak apical dominance and a low shade tolerance the results may be evident within a few years.
It depends a lot on whether it is a single line of trees along the roadside (like an avenue), in which case I would expect them to be more or less symmetrical, or a road cut through a densely wooded area, in which case I would expect the trees to preferentially grow into the clearing above the road.
I actually have a whole clump of conscious, reasoning, mobile trees. It keeps the local crime rate right down, because all the miscreants know that if they give me any trouble, all I have to do is call the copse.