Sound from a motorway, a railway and an aircraft approach spreads over a district of 89 buildings. Barriers and buildings diffract it; the map and the readouts update live.
Open-field transect, receiver 4 m high. White: current barrier setting. Grey: no barrier. Dashed: free-field line-source law (-3 dB per doubling).
Sweeps wall height from 0 to 8 m at the probe, motorway only, with the buildings in place.
The science
Decibels. L = 10 log10(I / I0), I0 = 1 pW/m2. Levels from independent sources add as energies: 60 + 60 = 63 dB, not 120. A-weighting A(f) (IEC 61672) discounts low frequencies the ear hears poorly.
Sources. Road: per-vehicle sound power Lw = 100 dB (cars) / 110 dB (heavy) at 70 km/h, +30 log10(v/70) (tyre and engine noise grow roughly with v3), spread over the road as W' = (Q / 1000v) 10Lw/10 W per metre for Q vehicles per hour. Rail: 96 dB per metre of train at 100 km/h, scaled by the fraction of time a trains occupies the track. Aircraft: 140 dB(A) per approach, spread along the path by flights per hour. These are typical orders of magnitude, not measurements of a real road: spot-check them before using any number for planning.
Propagation. Each source line is cut into point sources every 25-40 m. Geometric spreading 1/(2 pi r2) for ground-level sources (half space) and 1/(4 pi r2) for the aircraft; a line of such points gives Lp = Lw' - 3 - 10 log10 r (-3 dB per doubling) while one point gives -6 dB. Air absorption alpha = 0.4 / 1.9 / 9.7 dB per km at 125 / 500 / 2000 Hz (ISO 9613-1, 20 C, 70 % RH). Ground effect uses the ISO 9613-2 alternative Agr = 4.8 - (2 hm / d)(17 + 300 / d).
Barriers and buildings. For every source-receiver pair the plan view is tested for a wall in the way; if the top breaks the line of sight the path difference is delta = a + b - c and the screening is Dz = 10 log10(3 + 20 N), N = 2 delta / lambda (Maekawa, as in ISO 9613-2), limited to 20 dB for walls and 10 dB for building roofs (their side paths are not modelled). Because lambda is shorter at 2 kHz than at 125 Hz, barriers cut high frequencies more: the solver runs three octave bands (125 / 500 / 2000 Hz) and adds them as energy. An ideal half-plane (Kirchhoff, Fresnel integrals) gives 10 log10(2) = 3 dB more loss than Maekawa; the page checks that gap.
Lden. Lden = 10 log10[(12 * 10Ld/10 + 4 * 10(Le+5)/10 + 8 * 10(Ln+10)/10) / 24], day 07-19, evening 19-23, night 23-07 (EU Directive 2002/49/EC). A constant 60 dB gives 66.4 dB. Hourly traffic factors are illustrative profiles. WHO 2018 guideline values quoted are road 53, rail 54, aircraft 45 dB Lden (typical values, check the WHO document). Annoyance uses the road-traffic fit %HA = 78.927 - 3.1162 L + 0.0342 L2 (Guski et al. 2017).
Simplifications. Single diffraction only, no diffraction round building corners or double barriers, no reflections or scattering from facades, no wind/temperature gradients, no vegetation, three bands instead of full spectra, constant speeds, no tonal/impulsive penalties, vehicles rendered as one line source in the road centre, the district layout is invented. Educational model, not for planning or legal noise assessments.
Made with Blender-baked textures and models, Three.js and WebGL.