Opportunities

OPPORTUNITIES

The scope for roadside planting is enormous. Roadside vegetation has multiple benefits (see box 12.1), including creating barriers against road dust. Trees and shrubs especially can trap the dust with their leaves, minimizing the amount of dust reaching farms and houses. There is little research on how effectively roadside tree lines intercept dust; however, Maher et al. (2013) indicate that roadside tree planting can reduce particulate matter by more than 50 percent, and even more if the leaves are hairy. Moreover, trees provide shade and contribute to beautification. Beautification is a significant service because large numbers of people walk along the roadside in many countries.

Roadside vegetation can also protect the road. Grasses in particular can help reduce runoff velocity and trap sediments, thus reducing roadside erosion. In some waterlogged areas, trees that consume large quantities of water (such as eucalyptus) can be used to dry the road subgrade and help protect the road. furthermore, roadside plantings will not only check deterioration of roads and the environment but will also create productive assets for local communities. Productive benefits can be derived from the direct benefits of trees—such as timber and fruit harvesting—and by their acting as windbreaks that reduce desiccation and wind erosion. as noted earlier in these guidelines, any tree planting where trunks will achieve a diameter greater than 75 millimeters in due course should be located a substantial distance from the edge of the road (probably a minimum of more than 20 meters from the carriageway, and farther where travel speeds are greater than 50 kilometers an hour). Provided that safe sightlines are maintained, shrubs with full-grown diameters of less than 75 millimeters can be used nearer to roads because they pose much less risk to the health of vehicle occupants. Where planting already exists or planting closer to the carriageway is considered necessary, appropriate safety barriers are required to protect vehicle occupants from crashes into tree trunks.

BOX 12.1

Advantages of roadside vegetation

Roadside vegetation offers a number of positive attributes.

• Removes dust and other pollutants from the air, protecting crops, roadside communities, and livestock • Reduces soil erosion; holds soils in place • Creates wind breaks to reduce desiccation and wind erosion • enhances flood control by slowing and absorbing road runoff • Provides carbon dioxide sequestration • Produces direct benefits, such as timber, fodder, fuelwood, fruits, pollinator habitat • Provides shade and keeps the road cool for road users • Beautifies roadsides • Improves visibility • Can be used to guide road speed