What also this salting do to the plant along roadsides why

Solution:

The foliage on roadside vegetation is damaged when salted water sprays up from the pavement by passing vehicles. Salt-laden water can also percolate down through the soil profile, coming into contact with soil particles, soil microbes, and plant roots.

One way that salt can harm soil is that excess salt in the soil can kill off plants and thus cause soil erosion. Excess concentrations of salts dissolved in soil water are harmful to the plant in two ways. One way is by osmotic influences and the other by specific ion toxicities.