Noise from Road and Railway Tunnels

Noise from the Tunnel Mouth New Object type tunnel opening available from SoundPLAN 7 Object is digitized using two points Propagation of the noise always 90° left of the data entry direction

Important details of the tunnel object Shape of the tunnel mouth can be selected to be either a rectangle or a half circle Width, height and length of the tunnel can be defined The tunnel can be split into 2 sections of different absorption of the tunnel walls. Selection of the absorption spectrum for each tunnel section out of four pre-defined spectra. Noise from the Tunnel Mouth

Positioning the tunnel mouth on the road/rail segment Width Base height change Distance to the road/rail alignment Reverse the direction the noise from the tunnel is transmitted distance width axis distance < 0 distance = 0distance > 0 Noise from the Tunnel Mouth

Sound propagation from tunnels All roads/railway lines intersected by the tunnel object contribute to the emission. The emission noise level in the tunnel mouth is used for the noise inside the tunnel. Road and rail segments inside the tunnel for the „normal“ calculation have their emissions set to 0.0 dB. The tunnel mouth is simulated by 4 point sources. The noise propagation is calculated in accordance to the ISO , regardless of the standard used for the calcultion of the road/rail. Noise from the Tunnel Mouth

Sound propagation from tunnels For roads the directivity correction dL(Φ) is used. For the reference case with smooth concrete surfaces the directivity is represented by the diagram below: The directivity on top of the tunnel is set to the value found for 90° in the diagram. For the calculation of the screening by the tunnel mouth extra geometry must simulate the landscape on top of the tunnel (use elevation lines, noise barriers etc). Noise from the Tunnel Mouth

Theory: Theory: Noise propagation from tunnels The propagation loss (as a factor, not in dB) from a stationary point source in the distance x to the tunnel opening is set to [1]: (For a tunnel with a semi circle cross-section): (For a tunnel with a rectangular cross-setion:) With: r: tunnel radius [m] w: half the width of the tunnel mouth [m] h: height of the tunnel [m] a: parameter for the sound absorption of the tunnel (0 =1) a needs to be: with α being the absorption coefficient of teh tunnel walls Noise from the Tunnel Mouth

If the line source inside the tunnel has a sound power per meter L’w, the power transiting teh tunnel mouth amounts to: With L: tunnel length [m] If the L’w is constant within the tunnel: When the tunnel portal is clad with absorbent material, use the equation [2]: With a1: absorption coefficient in the area 1 (0..x1) a2: absorption coefficient in the area 1 (x1..L) x1: distance from the tunnel mouth to where a different material with different absorption coefficient was used (x1) Noise from the Tunnel Mouth

If the L’w within the tunnel is constant: Directivity: For roads the directivity correction dL (Φ) applies. The values for the reference case (smooth concrete surface) is set to: angle Φ [deg]frequency range [Hz] < > > See diagram Noise from the Tunnel Mouth

For the non-standard case the difference level between the sound power at the tunnel mouth for the reference case and the non-reference case is calculated an the directivity is adjusted in accordance to the table below. Intermediate angles are derived by linear interpolation. The directivity already contains screening effects. These screening effects are calculated explicitly, therefore the program sets the directivity dL( °) = dL(90°). Noise from the Tunnel Mouth

Literaure: [1] K. Takagi et.al., Prediction of Road Traffic Noise around Tunnel Mouth Proc. Internoise 2000, pp [2] Jonasson, Storeheier, Nord New Nordic Prediction Method for Road Traffic Noise, Version 1.0, [3] Jonasson, Storeheier, Nord New Nordic Prediction Method for Rail Traffic Noise, Version 1.0, Noise from the Tunnel Mouth