Division: Impact noise (crossings, switches and junctions) - Commission Directive (EU) 2015/996 of 19 May 2015 establishing common noise assessment methods according to Directive 2002/49/EC of the European Parliament and of the Council (Text with EEA relevance)

Impact noise can be caused by crossings, switches and rail joints or points. It can vary in magnitude and can dominate rolling noise. Impact noise shall be considered for jointed tracks. For impact noise due to switches, crossings and joints in track sections with a speed of less than 50 km/h (30 km/h only for trams and light metro), since the minimum speed of 50 km/h (30 km/h only for trams and light metro) is used to include more effects according to the description of the rolling noise chapter, modelling shall be avoided. Impact noise modelling shall also be avoided under running condition c = 2 (idling).

Impact noise is included in the rolling noise term by (energy) adding a supplementary fictitious impact roughness level to the total effective roughness level on each specific j-th track section where it is present. In this case a new L_{R,TOT + IMPACT,i} shall be used in place of L_R,TOT,i and it will then become:

L_{R,TOT + IMPACT,i} = 10 \times \lg (10^{L_{R,TOT,i} ∕ 10} + 10^{L_{R,IMPACT,i} ∕ 10})

dB

(2.3.11)

L_R,IMPACT,i is a 1/3 octave band spectrum (as a function of frequency). To obtain this frequency spectrum, a spectrum is given as a function of wavelength λ and shall be converted to the required spectrum as a function of frequency using the relation λ = v/f, where f is the 1/3 octave band centre frequency in Hz and v is the s-th vehicle speed of the t-th vehicle type in km/h.

Impact noise will depend on the severity and number of impacts per unit length or joint density, so in the case where multiple impacts are given, the impact roughness level to be used in the equation above shall be calculated as follows:

L_{R,IMPACT,i} = L_{R, IMPACT - SINGLE,i} + 10 \times \lg (\frac{n_{l}}{0,01})

dB

(2.3.12)

where L_{R,IMPACT–SINGLE,i} is the impact roughness level as given for a single impact and n_l is the joint density.

The default impact roughness level is given for a joint density n_l = 0,01 m^–1, which is one joint per each 100 m of track. Situations with different numbers of joints shall be approximated by adjusting the joint density n_l . It should be noted that when modelling the track layout and segmentation, the rail joint density shall be taken into account, i.e. it may be necessary to take a separate source segment for a stretch of track with more joints. The L_W,0 of track, wheel/bogie and superstructure contribution are incremented by means of the L_R,IMPACT,i for +/– 50 m before and after the rail joint. In the case of a series of joints, the increase is extended to between – 50 m before the first joint and + 50 m after the last joint.

The applicability of these sound power spectra shall normally be verified on-site.

For jointed tracks, a default n_l of 0,01 shall be used.

Division Impact noise (crossings, switches and junctions)