Alpine Meadow Noise Monitor — Completed Study

Location 1 · Continuous highway noise monitoring near I-75

Monitoring period: Feb 14 – Apr 17, 2026

Duration: 62 days

Valid hours analyzed: 1,480

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

Hours Monitored

1,480hrs

Continuous measurement over 62 days

Daytime Exceedance

100%

of 924 daytime hours exceeded FHWA 67 dBA residential threshold

Nighttime Exceedance

100%

of 556 nighttime hours exceeded EPA 55 dBA threshold

Peak Sound Level

112dBA

Apr 17, 11:13 AM · Overall L_Aeq 76.1 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 924 daytime hours exceeded 67 dBA

Every single daytime hour of the 62-day study exceeded the FHWA residential noise threshold.

Nighttime (10 PM – 7 AM)

100%

of 556 nighttime hours exceeded 55 dBA

The quietest hour of the entire study — Sunday, Feb 22 at 4:00 AM — measured 65.4 dBA, still more than 10 dB above the EPA nighttime threshold. All ten of the study's quietest hours occurred between midnight and 5 AM.

A notable event

April 17, 2026 · 11:13:28 AM

112 dBA

Peak instantaneous reading

At 11:13 AM on April 17, the monitor captured a 112 dBA peak — a level consistent with a heavy commercial vehicle passing at close range on the interstate.

The event showed a characteristic 13-second Doppler-asymmetric pass-by signature: rapid rise, peak, and gradual decay consistent with an approaching and departing source on a fixed path. Weather-flagged samples for the containing hour were zero — no precipitation, no high wind. This was a clean acoustic event, not instrumentation artifact.

For context, sustained exposure above 85 dBA is considered potentially harmful to hearing by OSHA. Brief peaks at 112 dBA are comparable to power tools operated at close range.

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).
Sampling: One reading per second, continuously. Hourly statistics computed only for hours with ≥ 2,700 samples (75% coverage) to exclude partial hours. Of 1,491 hour-slots in the window, 1,480 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 76.1 dBA is energy-averaged across all 1,480 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 112 dBA peak on Apr 17 was the highest; the top five peaks were all ≥ 105 dBA, distributed across the monitoring window.
Weather flagging: Samples taken during precipitation or sustained wind ≥ 15 mph are flagged from NOAA KTYS (McGhee Tyson Airport) observations. Sensitivity check: the 30-day aggregate L_Aeq shifts by only ~0.57 dB when all flagged readings are excluded — 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: Nine hour-slots in the window have no recording: a single 6-hour interruption on Feb 20 (12:00 – 17:00 ET), plus three isolated single-hour gaps on Feb 22, Feb 26, and Mar 8 (the last of which corresponds to the “spring forward” DST transition, so represents no actual elapsed time). Two additional hours recorded but fell below the 75% coverage threshold: the deployment startup hour (Feb 14 13:00) and the recovery hour immediately following the Feb 20 interruption (Feb 20 18:00). Likely cause of the Feb 20 interruption was a hung reboot; no sensor malfunction occurred during the study. These gaps do not affect the percentage-of-hours statistics above, which are computed against the 1,480 valid hours that met the coverage threshold.