Pollutants produced by highway traffic cause significant environmental damage, both in terms of air quality and on use of rural land through which highways run. Dust from highway traffic causes contamination of agricultural produce, and the construction of roads also contribute to territorial fragmentation, with consequent loss of continuity within ecosystems.
The SHIDRA project aimed to mitigate the environmental impact (in terms of air quality and on agricultural soil quality) of the construction of new roads, especially motorways, which cut through rural areas. Located in the Po Valley in Lombardy, the project aimed to create plant corridors along the roadside to act as barriers to ‘trap’ the particulate matter emitted by road traffic pollutants and prevent its diffusion into the wider rural area. The overall objective was to develop specially-designed (based on their geometric shape and mix of vegetation species) dust-trapping barriers along an 8 km stretch of motorway between Val Trompia (in the province of Brescia) and Fascia dei Fontanili in Cremona province. The roof-shaped barriers, built 15-20 metre in depth, would operate both as habitat hedges for wildlife and as an ecological corridor. Results would be monitored and the degree of reduction of pollutants assessed. Best use of financial resources normally paid to farmers in compensation for damages caused by new roads would also be examined. Finally, an experimental field would be established where different kind of vegetation structures (barriers) can be monitored using conventional automatic sampling devices and biological monitoring techniques.
Due to a number of delays, the project was unable to successfully meet its main objective (i.e. the construction of roof-shaped plant barrier along 8 km of highway). Only 200 metres was completed. However, the following secondary objectives were reached: The analysis of the plant barrier efficiency was undertaken through the examination of the different pollutants induced by road traffic: dust (PM 10 and PM 2.5), pollutant gases (CO, NOx, benzene), and heavy metals (Cd, Cr, Cu, Ni, Zn, Pb). The ‘filtering’ effect was also confirmed. Monitoring of this activity was only performed along an existing plant barrier near Persico in the province of Cremona, and has shown a decreasing of PM-10 pollutant dispersion from the highway to the country by 9% to 28% (depending on seasonal changes).
The plant barriers constructed in Persico and Lograto (Brescia) – consisting exclusively of ‘autochthonous’ species (i.e. descended from the original flora, fauna, or inhabitants of the region in which it is found) with a lot of shrubs – have provided an important wildlife corridor connecting the Val Trompia region to the plain and wet areas around the Mella River, near Brescia. Evidence of this was provided by a fauna monitoring campaign carried out at Persico Dosimo – where the roof-shaped barrier is already five years old.
The results indicate that species such as the common sparrow (Passer domesticus) and blackbird (Turdus merula) arrived first and have been followed year on year by other species including the European brown hare (Lepus europaeus), hedgehogs, moles, mice and the less common, hazel dormouse (Muscardinus avellanarius).
Finally, a study of the feasibility of wood production along autoroutes has been carried out and followed up by a first example of short rotation forestry (3.5 ha) implemented near the Mella River, within the project area.