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This study regarded the activities of the Italian Railway Network (RFI) connected with the Acoustic Remediation Plan (P.R.A.) for the buildings located near the Castiglioncello-Rosignano stretch of the Pisa-Roma rail line, and in particular in the municipality of Rosignano Marittimo (Livorno).
The work is part of a more general plan of noise reduction and abatement drafted by RFI pursuant to the decree of the Ministry of the Environment of 29/11/2000 (“Criteria for the preparation on the part of companies and entities managing public transport services or the pertinent infrastructures of noise reduction and abatement plans”). The work envisaged for the first 4 years of this plan, to be implemented over a period totalling 15 years, has been approved by the Joint Conference of the State and the Regions.
Specifically the project for the municipality of Rosignano regards a stretch identified with the following work codes: C.I. 049017056 and C.I. 049017031, shown in red in the orthophoto below.
The study was carried out in accordance with the indications provided in the regulations governing the sector, and specifically:
In compliance with the regulations governing this phase, the study was carried out on receptors located in land area “A” of the railway, i.e. the area comprised within 0 and 100 metres from the centre line of the external track of the rail line. Where sensitive receptors were present, the study was extended to 250 metres. Shown below is the area covered by the survey on an orthophoto.
So the initial input for the project was the Acoustic Remediation Plan drafted by RFI, compared to which the noise mitigation works in height and extension were redesigned.
Based on the noise level studies relating to the convoys travelling on the line, acoustic characterisation of the various types of trains present was carried out.
The same measurements were then used to calibrate the simulation model, and scenarios were verified relating to the two situations:
The impact produced by the railway infrastructures can be evaluated using dedicated mathematical simulation models. The acoustic impact of the line analysed was predicted and the noise abatement work dimensioned using the SoundPLAN simulation model (version 8.2).
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 standard used was the Deutsche Bundesbahn standard developed in accordance with Shall 03, while air absorption was evaluated in accordance with ISO 9613.
The input used for emission by the model was the LEQ at the reference distance of 25 m. This level can be calculated according to the Shall 03 standard, or, as in this case, it can be derived from data monitored or set by the user. The software calculates the propagation of noise in the area from the reference distance.
The application of the simulation model required the insertion of data regarding the following aspects:
The simulation of the existing situation was therefore set by taking account of the actual morphological characteristics of the site. The traffic used in the acoustic simulations is the traffic relating to the operations model for the rail line that runs through the municipality of Rosignano, i.e. the Pisa-Rome line. The analysis was carried out by calculating the traffic considering the category of the trains, the direction they are travelling in and the time bracket (day and night). The analysis considered the 30 days with the heaviest traffic in the last year of reference, based on which the project traffic was calculated, indicating the average number of trains that travelled on the line. As regards speed, the analysis adopted the speeds detected during the measuring campaign for the acoustic characterisation of the source.
In this project, the sound emission of the railway line entered into the simulation model was derived from a dedicated noise level study campaign, which divided the line into stretches with similar characteristics (how straight the line is, type of train, type and condition of the track, etc.) and similar traffic (travel speed, etc.)
These studies allowed us to obtain the value of the sound level to be assigned to the distance of 25 m used by the model as emission input for the standard used. We then verified the correct behaviour of the model by evaluating the differences between the values measured at the PS and PR positions and the values in the simulation. The acoustic analyses on the simulations performed with the aid of the model are considered reliable if the model has been calibrated with the effective emission and propagation conditions present at the site studied. In this case, the model showed small positive or negative differences compared to the values measured. Nonetheless, the differences encountered were within the range of precision required [±3 dB(A)].
Horizontal maps at a height of 4 metres were extrapolated from the calculation model for the diurnal and night reference periods (respectively, 6.00 a.m. to 10.00 p.m. and 10.00 p.m. to 6.00 a.m.), as were the acoustic impact values in front of the receptor.
Following the situation that emerged from the analysis of the existing acoustic climate, the noise mitigation work for the receptors affected by the noise were designed. Following the implementation of the indirect noise mitigation measures (noise barriers), almost all the receptors achieved noise levels below the regulatory limits during both reference periods (diurnal and night).
