This map shows modeled outdoor noise across Millbrae at 100-meter resolution, combining road, aviation, and rail sources. Green areas measure below 45 dBA. Orange and red exceed the EPA's 55 dBA outdoor threshold linked to long-term health effects. Use the layer toggles to view each source on its own or all together.
What the numbers sound like
- 30 dBAWhisper
- 40 dBASoft rainfall
- 45 dBAQuiet suburban street at night
- 50 dBAQuiet office
- 55 dBAEPA outdoor threshold: light traffic 100 ft away
- 60 dBANormal conversation an arm's length away
- 65 dBABusy restaurant
- 70 dBAHighway traffic 50 ft away
- 80 dBACity bus interior
Population Above the EPA Outdoor Threshold
The EPA's 55 dBA outdoor reference level is a common benchmark for residential noise exposure, especially for activity interference, annoyance, and long-term community noise concerns. About 10,465 Millbrae residents, or 48.9%, live above that level. By land area, 55.0% of Millbrae is above 55 dBA.
See how noise in Millbrae compares to similar-sized cities.
Noise by Part of Millbrae
Average noise levels for Millbrae residents, grouped by direction from the center of Millbrae. Northern Millbrae carries the highest population-weighted average; Central Millbrae carries the lowest. Just 37% of residents in Central Millbrae live in blocks above the EPA's 55 dBA threshold, about two-thirds of the share in Northern Millbrae.
Central Millbrae
37% of people above 55 dBA
Eastern Millbrae
65% of people above 55 dBA
Northern Millbrae
61% of people above 55 dBA
Southern Millbrae
42% of people above 55 dBA
Western Millbrae
35% of people above 55 dBA
Northern Millbrae sounds about 24% louder than Central Millbrae to the human ear, a 3.1 dBA gap. Every 10 dBA roughly doubles perceived loudness. Within any of these directions, two homes a quarter mile apart can still differ by 10 or more dBA depending on how close they sit to a major highway.
Loudest Road Corridors
The model evaluates every road in Millbrae using federal traffic counts, posted speeds, heavy-truck ratios, and pavement type. The source level shown is the modeled noise at the road centerline, where it is loudest. Noise drops with distance, faster in vegetated areas and slower over open pavement.
How far back from US Hwy 101 do you need to be?
US Hwy 101 produces an estimated 79 dBA at its loudest centerline points. Noise drops logarithmically with distance, with the exact rate depending on what's between you and the road. Tree cover, walls, terrain, and pavement type all matter. At roughly a quarter mile back, traffic fades into the noise level of a soft rainfall.
Calculated from the model's calibrated attenuation formula. About 9% of Millbrae sits under tree canopy (lighter than most cities) and roughly 51% is impervious surface like pavement and rooftops. Both are folded into the per-place decay rate above. Heavier canopy pulls noise down faster with distance; impervious surfaces slow the drop.
Rail Noise
Active freight rail runs through parts of Millbrae. For most blocks the rail-only contribution is small. Combined road-plus-rail noise rarely exceeds road noise on its own. The exceptions are the handful of blocks within roughly a quarter mile of the right-of-way during pass-through hours.
Use the Rail toggle on the map above to isolate rail's contribution from road and aviation.
Airport Noise
San Francisco International (SFO) sits northeast of Millbrae. The U.S. Department of Transportation measures aviation noise around this airport directly, and the model uses those federal measurements rather than synthetic predictions.
Blocks under the approach and departure paths carry combined road-plus-aviation noise, with some exceeding 95 dBA on the map's Overall layer. Blocks on the opposite side of Millbrae, particularly to the southwest, show no measurable aviation contribution. Use the Aviation toggle on the map above to isolate the airport's footprint.
How Noise Is Distributed Across Millbrae
The bar chart below shows the share of Millbrae residents in each noise band. About 49% of residents live below the EPA's 55 dBA threshold, and roughly 22% live in blocks above 60 dBA. Long-term exposure in that range is linked to elevated stress hormones and cardiovascular risk.
How Millbrae Compares
Millbrae sits at the louder end of the spectrum. Below: how Millbrae's average outdoor noise and share of residents above the EPA threshold compare with Burlingame, Belmont, San Lorenzo, and Pacifica.
Average noise level (dBA)
Millbrae's 56.2 dBA pop-weighted average is at the louder end of the spectrum. California as a whole averages 54.0 dBA and the U.S. averages 52.0 dBA. Both are lower than Millbrae because most of either area is rural land away from major roads.
Share of residents above 55 dBA
About 48.9% of Millbrae residents live in blocks where outdoor levels exceed the EPA's 55 dBA threshold. That's in the middle of its peer group. Measured by land area instead, 55.0% of Millbrae's footprint sits above 55 dBA, against a California average of 36.0% and a national average of 28.1%.
What This Means if You're Moving to Millbrae
- Distance from highways matters more than the neighborhood name. Two homes in the same zip code can differ by 20 dBA if one sits 100 meters from US Hwy 101 and the other 500 meters away. The model captures this at 100-meter resolution, so noise exposure changes block by block.
- Tree canopy can help reduce modeled noise exposure. Roughly 9% of Millbrae is under tree cover (lighter than most cities), and the dominant land cover is medium-intensity developed land. Both are measured from federal USDA Forest Service and USGS satellite imagery at 30-meter resolution. Streets with 60% or higher canopy show 3 to 5 dBA lower noise than comparable streets with bare ground or pavement, which is why the per-place decay rate above already accounts for it.
- Airport noise is directional. San Francisco International's approach paths concentrate aviation noise to the northeast. Neighborhoods to the southwest of downtown show no measurable contribution from the airport.
Sources & Methodology
The BestNeighborhood noise model is calibrated against nearly one million federal ground-truth measurements across four states. Road noise is computed from segment-level federal traffic data and propagated outward using physics-based acoustic decay, with attenuation rates that depend on the surrounding land cover.
Federal datasets used:
FHWA Highway Performance Monitoring System: road geometry, traffic counts, lane configuration
U.S. DoT Bureau of Transportation Statistics National Transportation Noise Map: aviation and rail noise, road calibration ground truth
USGS / MRLC National Land Cover Database: land cover and impervious surface coverage
USDA Forest Service Tree Canopy Cover: vegetation density for sound propagation
U.S. Census Bureau TIGER/Line: block-level geography and population
U.S. EPA Levels Document: 55 dBA outdoor reference level
All inputs are published federal datasets. Block-level noise is computed by combining road, rail, and aviation sound sources in the energy domain, the same physics used in professional environmental noise assessments. Read the full methodology.