Alpine Meadow Noise Monitor — Completed Study

Location 2 · Continuous highway noise monitoring near I-75

Monitoring period: Apr 29 – Jul 2, 2026

Duration: 64 days

Valid hours analyzed: 1,518

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

Hours Monitored

1,518hrs

Continuous measurement over 64 days — all 61 complete days exceeded the HUD 75 dBA L_dn “Unacceptable” threshold (75.8–79.9)

Daytime Exceedance

100%

of 949 daytime hours exceeded FHWA 67 dBA residential threshold

Nighttime Exceedance

100%

of 569 nighttime hours exceeded EPA 55 dBA threshold

Peak Sound Level

104dBA

May 14, 12:26 PM · Overall L_Aeq 74.8 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 949 daytime hours exceeded 67 dBA

Every single daytime hour of the 64-day study exceeded the FHWA residential noise threshold. The daytime L_Aeq of 76.1 dBA equals Location 1’s overall study average.

Nighttime (10 PM – 7 AM)

100%

of 569 nighttime hours exceeded 55 dBA

The quietest hour of the entire study — Sunday, May 3 at 3:00 AM — measured 64.7 dBA, still nearly 10 dB above the EPA nighttime threshold. All ten of the study's quietest hours occurred between 2 AM and 4 AM. Nighttime L_Aeq across the study was 70.6 dBA.

A notable event

May 14, 2026 · 12:26:01 PM

104 dBA

Peak instantaneous reading

At 12:26 PM on May 14, the monitor captured a 104 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: an 81 dBA baseline, a rapid spike to 104 dBA, and a gradual ~15-second decay consistent with an approaching and departing source on a fixed path. Weather-flagged samples for the containing hour were zero of 3,448 — no precipitation, no high wind. This was a clean acoustic event, not instrumentation artifact.

The study's top peak events measured 104, 101, 100, and 99 dBA, distributed across the monitoring window. For context, sustained exposure above 85 dBA is considered potentially harmful to hearing by OSHA.

Two locations, one conclusion

Study 1 (Location 1) vs. Study 2 (Location 2) — independent monitoring points along the same corridor

Location 1 · ~165 ft from I-75

76.1 dBA

Overall study L_Aeq

1,480 valid hours, Feb 14 – Apr 17, 2026. 100% of daytime hours exceeded the FHWA 67 dBA threshold; 100% of nighttime hours exceeded the EPA 55 dBA threshold.

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.

A second monitoring point ~20 ft farther from the interstate measured 1.3 dB lower overall — consistent with distance attenuation — yet every applicable federal threshold was still exceeded in 100% of qualified hours at both locations, across two seasons and two independent host properties. Location 2’s daytime L_Aeq (76.1 dBA) equals Location 1’s overall average.

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 1,537 hour-slots in the window, 1,518 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 74.8 dBA is energy-averaged across all 1,518 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 104 dBA peak on May 14 was the highest; the top events measured 104, 101, 100, and 99 dBA. (Two recorded peaks of 99 and 97 dBA one second 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: 7.28% of the study's 5,254,352 samples were flagged, and excluding all of them shifts the study L_Aeq by only 0.04 dB (74.75 → 74.79) — 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: Eighteen hour-slots in the window have no recording: a single 17-hour interruption on Apr 30 (approx. 1:00 – 17:00 ET) during deployment week, plus one isolated single-hour gap on May 15 (1:00 AM ET). One additional hour recorded but fell below the 75% coverage threshold: the recovery hour immediately following the Apr 30 interruption (Apr 30, 6:00 PM ET, 2,512 samples). No sensor malfunction occurred during the study. These gaps do not affect the percentage-of-hours statistics above, which are computed against the 1,518 valid hours that met the coverage threshold.