Alpine Meadow Noise Monitor — Completed Study

Location 2 · Study 3 · Continuous highway noise monitoring near I-75

Monitoring period: Jul 6 – Aug 6, 2026

Duration: 31 days

Valid hours analyzed: 744

Instrument: PCB Artists I2C SLM (IEC 61672 Class 2)

Hours Monitored

744hrs

Continuous measurement over 31 days — all 30 complete days exceeded the HUD 75 dBA L_dn “Unacceptable” threshold (76.8–79.9)

Daytime Exceedance

100%

of 465 daytime hours exceeded FHWA 67 dBA residential threshold

Nighttime Exceedance

100%

of 279 nighttime hours exceeded EPA 55 dBA threshold

Peak Sound Level

106dBA

Jul 17, 3:05 PM · Overall L_Aeq 75.0 dBA

What the thresholds mean

Federal standards referenced in this study

67 dBA daytime

FHWA Noise Abatement Criteria

23 CFR 772, Activity Category B

The Federal Highway Administration's threshold for residential land uses (homes, schools, places of worship). Exceedance triggers consideration of noise abatement measures in federally-funded highway projects.

55 dBA nighttime (10 PM – 7 AM)

EPA Outdoor Residential Level

EPA 550/9-74-004

The EPA's identified sound level below which no adverse effects on public health or welfare occur in residential areas. Applied here conservatively as an hourly threshold during nighttime sleep hours.

The full record

Hourly L_Aeq across the monitoring period · each point is one hour, separated by time of day, with the loudest sample per hour shown above

Loading hourly time series…

Daytime L_Aeq (7 AM – 10 PM)

Nighttime L_Aeq (10 PM – 7 AM)

Hourly peak (max instantaneous sample)

FHWA 67 dBA daytime threshold

EPA 55 dBA nighttime threshold

Day vs. night

Every hour of the study — day and night — exceeded its applicable federal threshold

Daytime (7 AM – 10 PM)

100%

of 465 daytime hours exceeded 67 dBA

Every single daytime hour of the 31-day study exceeded the FHWA residential noise threshold. Daytime L_Aeq across the study was 76.3 dBA.

Nighttime (10 PM – 7 AM)

100%

of 279 nighttime hours exceeded 55 dBA

The quietest hour of the entire study — Sunday, July 26 at 3:00 AM — measured 66.1 dBA, still 11 dB above the EPA nighttime threshold. All ten of the study's quietest hours occurred between 1 AM and 4 AM. Nighttime L_Aeq across the study was 71.1 dBA.

A notable event

July 17, 2026 · 3:05:57 PM

106 dBA

Peak instantaneous reading

At 3:05 PM on July 17, the monitor captured a 106 dBA peak — a level consistent with a heavy commercial vehicle passing at close range on the interstate.

The sample trace shows a characteristic pass-by signature: a 76 dBA baseline, a rapid spike to 106 dBA, and a gradual ~8-second decay consistent with an approaching and departing source on a fixed path. Weather-flagged samples for the containing hour were zero of 3,459 — no precipitation, no high wind. This was a clean acoustic event, not instrumentation artifact.

The study's top peak events measured 106, 103, 101, and 99 dBA, distributed across the monitoring window. For context, sustained exposure above 85 dBA is considered potentially harmful to hearing by OSHA.

One location, two studies

Study 2 vs. Study 3 — the same monitoring point at Location 2, two monitoring periods

Study 2 · Location 2, ~185 ft from I-75

74.8 dBA

Overall study L_Aeq

1,518 valid hours, Apr 29 – Jul 2, 2026. 100% of daytime hours exceeded the FHWA 67 dBA threshold; 100% of nighttime hours exceeded the EPA 55 dBA threshold.

Study 3 · Location 2, ~185 ft from I-75

75.0 dBA

Overall study L_Aeq

744 valid hours, Jul 6 – Aug 6, 2026. 100% of daytime hours exceeded the FHWA 67 dBA threshold; 100% of nighttime hours exceeded the EPA 55 dBA threshold.

Two monitoring periods at the same point measured 74.8 and 75.0 dBA overall, and every applicable federal threshold was exceeded in 100% of qualified hours in both studies.

Methodology & data integrity

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Instrument: PCB Artists I2C Decibel Sound Level Meter with ARM Cortex M4, pre-calibrated dB SPL output. Designed according to IEC 61672 Class 2 guidelines. A-weighted, FAST time-weighting (125 ms).
Calibration: A field comparison was conducted between the PCB Artists I2C Decibel sensor and a Lutron SL-4030 IEC 61672 Class 2 sound level meter (factory calibration certificate). Two test signals were used: a 1 kHz reference tone (60–87 dBA) and broadband pink noise (~85 dBA). On the 1 kHz tone, the PCB Artists read 1–2 dBA below the Lutron with consistent offset across the tested range. On broadband pink noise, the PCB Artists read approximately 2 dBA above the Lutron — a frequency-dependent reversal consistent with the wider Class 2 tolerances at low frequencies. For broadband traffic noise, which spans both regimes, the net offset between the two instruments falls within the combined ±2–3 dB Class 2 tolerance envelope and no single-value correction is defensible. Reported values in this study are uncorrected PCB Artists sensor readings.
Sampling: One reading per second, continuously. Hourly statistics computed only for hours with ≥ 2,700 samples (75% coverage) to exclude partial hours. Of 744 hour-slots in the window, all 744 met the coverage threshold and are used for the statistics above.
Hourly averaging: L_Aeq,1h using energy averaging (logarithmic mean per IEC 61672). This correctly weights loud transient events rather than underweighting them as an arithmetic mean would. Overall study L_Aeq of 75.0 dBA is energy-averaged across all 744 valid hours.
Percentiles: L₁₀ and L₉₀ computed using the nearest-rank percentile method on the full set of samples in each hour.
Peak detection: L_Amax FAST peak detection on the instantaneous sample stream, preserving sub-second events. The 106 dBA peak on July 17 was the highest; the top events measured 106, 103, 101, and 99 dBA. (Two recorded peaks of 102 and 103 dBA two seconds apart were the same pass-by event and are counted once.)
Weather flagging: Samples taken during precipitation or sustained wind ≥ 15 mph are flagged from NOAA KTYS (McGhee Tyson Airport) observations. Sensitivity check: 6.28% of the study's 2,573,745 samples were flagged, and excluding all of them shifts the study L_Aeq by only 0.03 dB (75.00 → 75.03) — headline findings are robust to weather contamination.
Data capture: Primary logging to local SQLite on the Pi (data integrity). Parallel MQTT publish to cloud for dashboard. Offline periods are caught up automatically when connectivity returns — no data is lost to network outages.
Known gaps: None. All 744 hour-slots in the window were recorded and met the 75% coverage threshold. One hour (Jul 6, 8:00 PM ET) is computed from 3,033 of its 3,447 recorded samples after a software restart part-way through the hour; recomputing it from all samples changes that hour by 0.14 dB and no figure on this page. No sensor malfunction occurred during the study.