What causes the side of my tree facing the road is brown and dying?

Sodium chloride applied to roads, driveways, and sidewalks through central Indiana winters, delivered two ways: thrown as aerosol by traffic and plows well beyond the pavement edge — farther along high-speed roads — and carried in meltwater into the root zone, concentrated wherever runoff collects or plowed snow is piled. Homeowner salt on driveways and walks, and plow piles dumped into a planting bed, are as common a source as the highway. Clay soils hold sodium tightly and release it slowly, so central Indiana soils accumulate across winters instead of flushing after one. Species choice decides how much shows: sugar maple, white pine, hemlock, littleleaf linden, and red maple are sensitive; honeylocust, hackberry, Kentucky coffeetree, white oak, juniper, and Austrian pine are more tolerant.