Day 11 Senses: Sound — The sound of the road outside the hospital
A transparent road-noise model for Dhaka and Chattogram, tested against the WHO 53 dB guideline, with sliders so you can change every assumption — and a button to hear it. Dhaka: 17.7% of 10.3 million people live where modelled road noise is at or above the WHO 53 dB guideline. Chattogram: 21.5% of 3.3 million people live where modelled road noise is at or above the WHO 53 dB guideline.
Write-up
The question
How loud is the road outside the hospital? Where do people and health facilities in Dhaka and Chattogram sit above the WHO 53 dB road-noise guideline?
Data
BD Hospital Dataset (hospitals, clinics, pharmacies), fire stations, garment factories, economic zones and major roads from the GIS Data folder; BBS Population and Housing Census 2022 thana populations; city-corporation boundaries. The registry is incomplete and urban-biased; population per 250 m cell is a dasymetric model; distances are straight lines in UTM 46N.
Methods
- Study areas: the two Dhaka city corporations (DNCC + DSCC, 53 thana polygons, 10,250,630 people) and Chattogram City Corporation (15 thanas, 3,273,329 people), BBS Population and Housing Census 2022. White gaps on the maps are outside the corporations (cantonment, airport, water).
- Health facilities: the BD Hospital Dataset in the GIS Data folder, split into hospitals, clinics and pharmacies from the type and name keywords; pharmacies within 25 m of each other merged; an ‘emergency / 24 h’ flag from the name and type. Dhaka: 475 hospitals, 507 clinics, 2,049 pharmacies, 44 fire stations. Chattogram: 160, 51, 405 and 24.
- Where people live: the census gives thana totals only, so each thana total is spread over a 250 m grid in proportion to a Gaussian kernel (σ = 400 m) of settlement proxies — mobile-phone towers, mosques, schools, health points, pharmacies, hospitals — plus a small floor. Cell sums equal the census total exactly (checked).
- Road layer: country-major.geojson (national, regional, zila and upazila roads) clipped to each city; each road is cut into 20 m elements.
- Source level at 10 m by class (assumed LAeq, dB): NH 78, RH 75, ZR 71, UZR 66. Sound energy reaching a 250 m cell centre = sum over elements of 10^(L/10) · (10·s/π) / r² · 10^(−α·r/10), r ≥ 8 m, α = 0.012 dB/m, radius 900 m (line source with spherical spreading and air absorption).
- Total level = 10·log10(road energy + back-street floor energy), floor 45 dB; bands at 50, 53 (WHO Lden guideline for road traffic), 55, 60, 65 and 70 dB; means are energy means, never averages of dB.
- Web sandbox: the model is linear in energy, so the page stores the unit energy of each road class for every cell and recomputes all 4,563 cells and 982 health points in the browser when you move a slider.
Findings
Dhaka — With round-number source levels (national highway 78 dB, regional 75, zila 71, upazila 66 at 10 m) and a 45 dB back-street floor, 17.7% of Dhaka people are at or above 53 dB, 8.4% at or above 60 dB and 1.7% at or above 70 dB.
Dhaka — 188 of 475 hospitals (40%) sit at or above the WHO guideline, 71 at or above 65 dB — the road outside, not the ward inside.
Dhaka — Loudest thanas (energy-average, people weighted): Shere Bangla Nagar (DSCC) 71.8 dB, Uttara Purba 69.3 dB, Tejgaon Shilpa Elaka 68.0 dB.
Dhaka — Noisiest hospital sites in the model: BSMMU Outdoor 1 (Medicine) (79.8 dB), Al Ihsan Hospital (79.7 dB), Tairunnessa Memorial Medical College And (79.5 dB).
Chattogram — With round-number source levels (national highway 78 dB, regional 75, zila 71, upazila 66 at 10 m) and a 45 dB back-street floor, 21.5% of Chattogram people are at or above 53 dB, 9.3% at or above 60 dB and 1.9% at or above 70 dB.
Chattogram — 56 of 160 hospitals (35%) sit at or above the WHO guideline, 11 at or above 65 dB — the road outside, not the ward inside.
Chattogram — Loudest thanas (energy-average, people weighted): Chalk Bazar 66.0 dB, Pahartali 62.7 dB, Halishahar 62.2 dB.
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