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The road in the project is a dual carriageway, with two lanes per direction. The stretch covered by the project is approx. 32 km long, and is located partly near the current area of the Via Cassia and partly in less anthropized areas; it will comprise 14 viaducts and 5 tunnels. A speed of 130 km/h has been considered on the carriageways in the project, and 50 km/h on the slip roads. Noise reduction asphalt is used.
Acoustic study. The aim of this study is to specify the location, type and method for the construction of noise mitigation works for the project for the completion of the work to make the SR no. 2 Via Cassia a four-lane road.
The noise level estimate was conducted using the SoundPlan model (version 7.4). SoundPlan is an elaborate noise simulation model, based on the Ray Tracing technique, which can be used to simulate the propagation of noise in complex source and orography situations. The calculation model for the road axis is the French method NMPB Routes 96, with a number of rays equal to 100 and a number of reflections equal to 5. The propagation distance has been considered up to 1000 metres. The noise level estimate takes account of traffic composition, number and speed of vehicles, the type of asphalt and the slope of the road. The high quantity of initial information, together with the level of precision set at the data processing stage, yields results that are very accurate, although onerous in terms of calculation resources. The calculation model for the road axis is the French method NMPB Routes 96, with a number of rays equal to 100 and a number of reflections equal to 5.
Extrapolated from the calculation model were the horizontal maps at an altitude of 2 metres (in accordance with the characteristic reception altitude of the area) and the vertical sections with standard-type conditions at the propagation line (sigma=600).
Noise barriers were designed for the points at which noise levels exceed the permitted threshold. The barriers were constructed taking account of the surrounding environment, with a preference for natural, breathable materials (barriers of a mixed type, in wood/PMMA) and shielding elements integrated into the natural environment (noise reduction walls). The solid panels were used only for technical reasons regarding the positioning on the stretches on the viaduct (integrated metal barriers), or the need to obtain superior acoustic performance (wooden barriers). The RAL colours of the metal barriers were in any case chosen to blend as smoothly as possible with the surrounding landscape, matching the colour of the wooden barriers.
Air study. The estimate of air pollution dispersion caused by vehicular traffic with the road in operation was conducted by simulation using the CALINE4 air dispersion model (implemented into the MMSCaline software). CALINE belongs to the category of Gaussian models, and specifically takes account of the linear form of the source and the turbulence induced by the movement of the motor vehicles. NOx, CO and PM10 emissions were evaluated.
