plant trees and flowering bushes
Peepul and neem trees are very suitable for roadside plantation. Peepul is a big spreading tree with many leaves. It is a good producer of oxygen and thus an air purifier.
But you should also consider flowering trees which produce beautiful flowers and thus add beauty to the landscape. Some good flowering trees are: gulmohar, spathodea,amaltas, jacaranda, cassia,silk cotton tree,erythrina,bauhinia (kachnar),champa (michelia champaca),frangipani(plumeria alba). There are also many flowering bushes which you can plant for beautiful flowers like oleander and krishnachura etc.
Contact the forest nurseries in your area. Most of them produce tree saplings in bulk on demand from customers. These saplings are sold at govt. subsidized rates. For a better response, meet the Conservator in your area first and he /she will them direct you to the nearest forest nursery where you can place your order. You will have to find out the rates of various trees from the forest nursery staff as they vary from place to place and from nursery to nursery. Good luck and happy planting!
