Sources & methods

Roads and traffic

Caltrans State Highway Network (SHN) Lines (route geometry with postmile/odometer)

California Department of Transportation (Caltrans). Published by Caltrans without a dataset-specific licence. Credit: California Department of Transportation (Caltrans) Route geometry used to match counts to roads.

Caltrans Traffic Volumes AADT (State Highway System count points, LA County)

California Department of Transportation (Caltrans), Traffic Census Program. Published by Caltrans without a dataset-specific licence (state copyright notice, public agency data). Credit: California Department of Transportation (Caltrans) Annual average daily traffic on state highways.

Caltrans Truck Volumes AADT (truck census, LA County)

California Department of Transportation (Caltrans). Published by Caltrans without a dataset-specific licence. Credit: California Department of Transportation (Caltrans) Truck share on state routes.

FHWA Highway Performance Monitoring System (HPMS) 2024 Spatial All Sections, Los Angeles County rows

U.S. Department of Transportation, Federal Highway Administration (FHWA), Office of Highway Policy Information (via data.transportation.gov dataset 42um-tgh5). U.S. Government public domain. Credit: Federal Highway Administration, HPMS 2024 Traffic counts on federal-aid roads.

LA County Public Works Traffic Count table (MapServer layer 59)

County of Los Angeles, Department of Public Works (DPW). LA County eGIS terms of use (open use, as is). Credit: County of Los Angeles Public Works

LADOT Traffic Counts Summary (Socrata 94wu-3ps3) and located-on-TIGER derivative

City of Los Angeles, Department of Transportation (LADOT) via data.lacity.org. CC0 1.0 (public domain dedication). Credit: City of Los Angeles, LADOT traffic counts Used for city street counts.

OpenStreetMap SoCal extract (Geofabrik socal-261003.osm.pbf) and derived LA County highway/bridge/barrier files

OpenStreetMap contributors; extract processed by Geofabrik GmbH. Open Database Licence (ODbL) 1.0. Street types, bridges, barriers; extract by Geofabrik.

U.S. Census Bureau TIGER/Line 2025 Edges, Feature Names and All Roads, Los Angeles County (06037), plus current county boundary

U.S. Census Bureau, Geography Division. U.S. Census Bureau public data. Credit: U.S. Census Bureau, TIGER/Line 2025 Road network.

Buildings, terrain and ground

County 10 m terrain cache from USGS 3DEP 1 m DEM overviews (2023 lidar preferred), 129 tiles

U.S. Geological Survey (derived by Quiet LA with fetch_lidar_dem10.py). U.S. Government public domain. Credit: Courtesy of the U.S. Geological Survey, 3D Elevation Program 2023 lidar terrain at 10 m.

LA County Building Footprints (DPW MapServer layer 0, CODE='Building'; LARIAC-derived outlines with heights)

County of Los Angeles Department of Public Works (data originates from LA Region Imagery Acquisition Consortium, LARIAC). LA County eGIS terms of use. Credit: County of Los Angeles building footprints (LARIAC) Building footprints and heights.

LA County LARIAC Building Outlines (height-bearing; permitting.gis.lacounty.gov CSS_Viewable layer 3 and earlier pilot pulls)

County of Los Angeles / LARIAC. LA County eGIS terms of use. Credit: LARIAC, County of Los Angeles Building outlines with heights.

USGS 3DEP 1 m DEM, project CA_LosAngeles_B23 (4 pilot tiles) plus 1 m tile index for county

U.S. Geological Survey, 3D Elevation Program. U.S. Government public domain. Credit: Courtesy of the U.S. Geological Survey, 3D Elevation Program

USGS 3DEP 1/3 arc-second DEM tiles (n34w118, n34w119, n35w118, n35w119, n35w120)

U.S. Geological Survey, 3D Elevation Program. U.S. Government public domain. Credit: Courtesy of the U.S. Geological Survey, 3D Elevation Program Terrain fill where lidar is missing.

USGS 3DEP lidar point clouds (EPT) CA_LosAngeles_1_B23 via AWS usgs-lidar-public; corridor products (sound walls, bridge decks) and caches

U.S. Geological Survey 3DEP; hosted in AWS Open Data. U.S. Government public domain. Credit: USGS 3DEP LiDAR Point Clouds (registry.opendata.aws/usgs-lidar) Sound walls and bridge decks detected in the lidar.

Aircraft and airports

Contour source document for Brackett Field: Brackett Field Land Use Compatibility Plan (2015), received 2015-12-15

LA County ALUC / Brackett Field operator. Public agency reports. Source of official CNEL lines. (Brackett Field Land Use Compatibility Plan (2015), received 2015-12-15)

Contour source document for Burbank: Quarterly Noise Monitoring at Bob Hope Airport - 4th Quarter 2024, received 2025-02-04

Hollywood Burbank Airport / Burbank-Glendale-Pasadena Airport Authority. Public agency reports. Source of official CNEL lines. (Quarterly Noise Monitoring at Bob Hope Airport - 4th Quarter 2024, received 2025-02-04)

Contour source document for Fox Airfield: General William J. Fox Airfield Land Use Compatibility Plan - 12/1/04

LA County ALUC / Fox Airfield operator. Public agency reports. Source of official CNEL lines. (General William J. Fox Airfield Land Use Compatibility Plan - 12/1/04)

Contour source document for Hawthorne: Hawthorne Municipal Airport (2020), received 2022-09-06

City of Hawthorne / Hawthorne Municipal Airport (Jack Northrop Field). Public agency reports. Source of official CNEL lines. (Hawthorne Municipal Airport (2020), received 2022-09-06)

Contour source document for Long Beach: Long Beach Airport Noise Report - 4th Quarter 2024, received 2025-02-03

City of Long Beach (Airport). Public agency reports. Source of official CNEL lines. (Long Beach Airport Noise Report - 4th Quarter 2024, received 2025-02-03)

Contour source document for Los Angeles International: CA Airport Noise Standards Quarterly Report - 4th Quarter - LAX (2025), received 2026-03-26

Los Angeles World Airports (LAWA). Public agency reports. Source of official CNEL lines. (CA Airport Noise Standards Quarterly Report - 4th Quarter - LAX (2025), received 2026-03-26)

Contour source document for Santa Monica: Santa Monica Airport (2019) noise contours, received 2020-06-04

City of Santa Monica. Public agency reports. Source of official CNEL lines. (Santa Monica Airport (2019) noise contours, received 2020-06-04)

Contour source document for Van Nuys: CA Airport Noise Standards Quarterly Report - 1st Quarter 2026 - Van Nuys, received 2026-06-03

Los Angeles World Airports (LAWA). Public agency reports. Source of official CNEL lines. (CA Airport Noise Standards Quarterly Report - 1st Quarter 2026 - Van Nuys, received 2026-06-03)

Contour source document for Whiteman: Whiteman Airport Master Plan Update (2011), received 2021-06-15

County of Los Angeles Public Works (Aviation). Public agency reports. Source of official CNEL lines. (Whiteman Airport Master Plan Update (2011), received 2021-06-15)

Hollywood Burbank Airport quarterly noise monitoring reports 2014-2026

Hollywood Burbank Airport (Burbank-Glendale-Pasadena Airport Authority). Public agency reports. Credit: Hollywood Burbank Airport quarterly noise reports Used to check the aircraft estimate.

LA County airport noise contour polygons (35 features, CLASS 55-85 CNEL, 15 airports) - ALUC / Airport Land Use Plan layer

County of Los Angeles (Regional Planning, acting as Airport Land Use Commission); contour inputs from airport operators. LA County eGIS terms of use. Credit: County of Los Angeles Airport Land Use Plan noise contours Official CNEL contours.

LA County heliports/helipads (199 points, "HSIP Freedom Airports_Heliports")

Compiled by USGS & LA County (HSIP Freedom data; source-update epoch 2020-07-14), published on LA County eGIS. LA County eGIS terms of use. Credit: County of Los Angeles heliport locations Drawn as map context.

LAWA quarterly noise reports and maps for LAX and Van Nuys (monitor CNEL, contour maps)

Los Angeles World Airports. Public agency reports. Credit: Los Angeles World Airports noise reports Used to check the aircraft estimate.

Long Beach monthly noise reports and Santa Monica 2025 CNEL contours report; LAX/LGB/SMO monitor tables and position derivations

City of Long Beach; City of Santa Monica (HMMH report). Public agency reports. Credit: Long Beach Airport and Santa Monica Airport noise reports Used to check the aircraft estimate.

Rail

Amtrak GTFS static feed (partial tables: routes, trips, calendar, stops, stop_times)

National Railroad Passenger Corporation (Amtrak). Published schedule data; no licence text found. Credit: Amtrak published schedules Passenger train counts.

FRA Highway-Rail Grade Crossing Inventory (Form 71), LA County, Ventura/Valley subdivisions

US Federal Railroad Administration via data.transportation.gov (Socrata m2f8-22s6). U.S. Government public data. Credit: Federal Railroad Administration Freight train counts at crossings.

FTA Transit Noise and Vibration Impact Assessment Manual (Report 0123, 2018): reference SEL values (locomotive 92, rail car 82, horn 110 dBA at 50 ft, yard 118 SEL)

US Federal Transit Administration. U.S. Government public data. Credit: Federal Transit Administration, Transit Noise and Vibration Impact Assessment Manual Reference train levels.

Metrolink GTFS static feed

Southern California Regional Rail Authority (Metrolink). Published schedule data; no licence text found. Credit: Metrolink published schedules Passenger train counts.

OpenStreetMap railway ways, San Fernando Valley main lines + Van Nuys pilot box (Overpass extract)

OpenStreetMap contributors via Overpass API. Open Database Licence (ODbL) 1.0. Rail line geometry.

Weather and background sound

ASOS/METAR hourly weather observations (BUR, VNY, LAX, SMO, CQT 2021-2024; BUR, LAX, LGB, PMD 2020-2024) via Iowa Environmental Mesonet; NOAA/NCEI ISD pilot pulls

Iowa Environmental Mesonet (Iowa State University) redistributing NWS/FAA ASOS data; NOAA NCEI for ISD global-hourly. NOAA/NWS observations (public domain). Credit: NOAA National Weather Service ASOS via the Iowa Environmental Mesonet Typical-weather assumptions.

Hourly/5-min ASOS wind (direction, speed) for KLAX, KBUR, KLGB, KPMD 2020-2024 and derived wind climatology JSONs

NOAA/NCEI ASOS METAR (FAA/NWS stations); format matches Iowa State Univ. Iowa Environmental Mesonet (IEM) download. NOAA/NWS observations (public domain). Credit: NOAA National Weather Service ASOS via the Iowa Environmental Mesonet

ISO 9613-2 Annex A.2 housing-attenuation term (equation) and CNOSSOS-EU method references

International Organization for Standardization. Published standard (equation used; text not redistributed). Credit: ISO 9613-2, Annex A Housing screening term.

Sea mask from OSM natural=coastline (hum_v1/coast, sea.wkb)

OpenStreetMap contributors. Open Database Licence (ODbL) 1.0. Coastline for the distant-traffic layer.

Base map and addresses

"Photo" basemap: USGS National Map USGSImageryOnly raster tiles (hot-linked)

US Geological Survey, The National Map. U.S. Government public domain. Credit: Imagery: USGS Photo base map.

LA County Assessor parcel layer (LACounty_Parcel) and CAMS locator, used live for address lookup

County of Los Angeles (Assessor / Internal Services Dept eGIS). LA County eGIS terms of use. Credit: County of Los Angeles parcels and address data Address lookup in your browser; we do not receive the address.

NAIP 2022 0.6 m quarter-quads m_3411853_se_11_060_20220511.tif and m_3411854_sw_11_060_20220511.tif (Photo 3D colours)

USDA Farm Service Agency NAIP, via Microsoft Planetary Computer (anonymous SAS token). U.S. Government public domain. Credit: USDA National Agriculture Imagery Program, 2022 Photo 3D showcase.

Protomaps basemap fonts (glyph PBFs) and sprites, hot-linked from protomaps.github.io

Protomaps (github.com/protomaps/basemaps-assets). SIL Open Font Licence; MIT. Credit: Protomaps basemap fonts and icons

Protomaps basemap vector tiles, LA County extract la_county_20261004.pmtiles (234,993,401 bytes)

Protomaps (build of 2026-10-04; planetiler 0.10.2, basemap schema 4.15.2) from OpenStreetMap and Natural Earth. Open Database Licence (ODbL) 1.0. Base map vector tiles.

Terrarium elevation tiles for 3D terrain and hillshade (hot-linked)

Mapzen / Tilezen Joerd on AWS Open Data (elevation-tiles-prod). Free use under AWS Open Data terms. Credit: Terrain: Mapzen / AWS Open Data (terrain tiles built from USGS and other public elevation data) 3D terrain and hillshade.

USGS 3DEP lidar CA_LosAngeles_1_B23 (2023) EPT, extracted points for the showcase

US Geological Survey 3DEP (AWS usgs-lidar-public). U.S. Government public domain. Credit: Lidar: USGS 3DEP Photo 3D showcase.

Other context

City of Los Angeles Fire Stations (106 points)

City of Los Angeles Open Data (data.lacity.org rnb4-daiw), LAFD. CC0 1.0. Credit: City of Los Angeles Fire Department station locations Drawn as map context.

CNOSSOS-EU common noise assessment methods (Commission Directive (EU) 2015/996) and 2020 road coefficient amendment

European Commission / EU (JRC technical report EUR 25379 EN). EU legislation (Directive (EU) 2015/996). Credit: CNOSSOS-EU, European Commission The calculation method.

Front-end libraries shipped in the site bundle: maplibre-gl 6.9.0 (BSD-3), pmtiles 4.5.0 (BSD-3), @protomaps/basemaps 5.7.2 (BSD-3), three 0.186.1 (MIT), @sparkjsdev/spark 2.3.1 (MIT), next 15.5.24, react 18.3.1

respective authors (MapLibre contributors, Protomaps, three.js authors, World Labs/Spark). BSD-3-Clause and MIT open-source licences. Credit: Map software: MapLibre GL, PMTiles, three.js, Spark Open-source libraries.

LA County boundary (DPW countyboundary MapServer/0, OBJECTID 974, 88 land components)

County of Los Angeles Department of Public Works. LA County eGIS terms of use. Credit: County of Los Angeles boundary Defines the land area.

LA County Fire Department station locations (185 points)

County of Los Angeles Department of Regional Planning (DRP ESGV Safety Element MapServer layer 3). LA County eGIS terms of use. Credit: Los Angeles County Fire Department station locations Drawn as map context.

Measured road-noise set 2 (524 site rows, 171 with CNEL/Ldn) compiled from public environmental/planning documents, 2026-10-13

Compiled by Quiet LA from documents of LA Metro, Caltrans, City of Pasadena, City of LA Planning, LAWA, City of Long Beach, CEQAnet (State Clearinghouse), Port of LA, Cities of Carson/Irwindale/Santa Clarita/Malibu/Pico Rivera, County Planning and others. Public agency and environmental-review documents. Measurements used to check the model.

Measured-noise documents and extracted tables for validation set 1 (Caltrans/Metro/City EIR noise studies: SR-710 North, I-710 Corridor, I-105 ExpressLanes, I-405 Sepulveda Pass, I-210 La Crescenta, STCP, Wilmington/I-405, etc.) and airport monitor reports

LA Metro, Caltrans, City of LA, LAWA, Hollywood Burbank Airport, Long Beach Airport, Santa Monica Airport, CHSRA, others (some copies hosted by crescentavalleyweekly.com and sepulvedabasinwildlife.org). Public environmental-review documents. Measurements used to check the model.

noise_monitors.json: airport permanent-monitor CNEL and Metro Sepulveda Transit Corridor road 24-hour measurements (validation set 1) with source URLs

Compiled by Quiet LA from LAWA (LAX, Van Nuys), Hollywood Burbank Airport, City of Long Beach, City of Santa Monica quarterly noise reports and LA Metro Sepulveda Transit Corridor Project DEIR Appendix O. Public agency reports. Measurements used to check the model, not to tune it.

NoiseModelling 6.0.0 (noise engine; PathFinder patched copy; Quietla groovy scripts)

Universite Gustave Eiffel / CNRS (Noise-Planet, UMRAE). GNU GPL v3 (software). Credit: NoiseModelling, Université Gustave Eiffel / CNRS (Noise-Planet) Open-source noise engine implementing CNOSSOS-EU.

USDOT/BTS National Transportation Noise Map (2020 road, rail, aviation) via Esri Living Atlas tiled image service, LA County rasters

U.S. DOT Bureau of Transportation Statistics (BTS); hosted copy on Esri ArcGIS Online (Living Atlas). Federal public data. Credit: U.S. DOT Bureau of Transportation Statistics, National Transportation Noise Map Used only as a cross-check of freeway levels.

Road noise (the main layer)

A computer model, not a set of microphones. Quiet LA uses NoiseModelling 6, open-source software that implements CNOSSOS-EU, the European Union's common method for road, rail and aircraft noise. Every road in the mapped area is a sound source whose strength comes from how many vehicles use it, how fast they go and how many are trucks, for the day (7 am to 7 pm), evening (7 to 10 pm) and night (10 pm to 7 am). Traffic counts come from Caltrans, the Federal Highway Administration (HPMS) and the City of Los Angeles; where no count exists we use typical values for that kind of road, and those streets are estimates only. The model then works out how the sound spreads, how the ground absorbs it and how it bends over roofs, hills and freeway sound walls. Terrain is the 2023 USGS lidar scan at 10 m; sound walls found in the lidar and roads on bridges at deck height are included; buildings come from LA County footprints and heights. Reflections between buildings are not included. The weather assumed is typical for Los Angeles, with sound carrying farther in the evening and at night than in the day.

Day, evening, night and the 24-hour value

Day, evening and night values are average sound levels (LAeq) for each period at a point 4 m up and 2 m out from a building wall, or 1.5 m above open ground. The 24-hour value is CNEL (Community Noise Equivalent Level), the number most noise guidance uses: evening counts 5 dB more and night 10 dB more than the day to reflect sensitivity to noise at those hours. For buildings the map shows the loudest wall, and the panel also shows the least exposed wall.

Trains

On the Ventura and Valley main lines, sound from Metrolink, Amtrak and Union Pacific freight trains is calculated with the CNOSSOS-EU railway method, using published schedules, federal crossing counts and train types matched to US reference levels. Horn blasts before public grade crossings are included (a generic locomotive horn). Light rail and other lines are not included yet. Rail is added to road levels where it is modeled.

Aircraft

In the 24-hour view, aircraft noise is estimated from the official airport noise contours published in county land-use plans and quarterly airport noise reports. Official maps usually stop at 65 CNEL, so we extend each airport's contours down to 55 CNEL using the ratio between its two outermost official lines (dashed on the map). Contours older than the year 2000 are drawn for information but not counted. Compared with 57 permanent airport noise monitors the estimate is within about 3 dB on average, and it can read low far out along some approach paths. Helicopters and individual overflights are not modeled yet.

Open land (coarse estimate)

Parks, mountains and desert where the detailed model has no buildings are filled with a coarse estimate computed from freeways, ramps and major roads only, on a 100 m grid with no buildings and no local streets. Where the detailed model has a value, it always wins. Values here are rougher than in town.

Distant traffic hum

The detailed model looks 1.5 km out from each road. Traffic farther away still adds a low background hum, so a second, coarser calculation of freeways and major roads reaches 8 km on a 200 m grid, and the part beyond 1.5 km is energy-added to the map. Because that calculation has no buildings, a screening reduction based on how many buildings lie around each point (following the housing term of ISO 9613-2) is applied; its one scale factor was fitted so that basin residential areas read about 38 dB at night, in line with published residual-sound measurements. This layer is the least certain of the map.

Land far from major roads

Land with no freeway, ramp or major road within 3 km has no modeled value. It is shown with one low level (25 dB) and the label "Quiet: no freeway or major road within 3 km". That level is an assumption, not a computed or measured value; wildlife, wind, aircraft, local roads, construction and people can make such places louder.

How well it matches measurements

We compared the model with 564 public measurements around the county; about 160 had a 24-hour value and a usable map position. On average the model is within about 0.5 dB of them for the 24-hour level, and a typical single site is off by about 6 dB, higher or lower (part of that is not knowing exactly where each microphone stood). Near freeways the model runs about 4 dB loud on average with a wide spread, and for major streets the pattern differs by measurement year. We have not tuned the model to correct this, because the evidence does not yet support one simple correction.

What is not modeled

Construction, events, nightlife, neighbors, most helicopters, sirens, car horns, wildlife and the sound inside buildings. Blank areas are not modeled yet; blank never means quiet. Results use typical weather and traffic, not the conditions on any particular day.