Chapter 1 - Caltrans - State of California

Chapter 3 Comments and Coordination
ranged from 50.0 to 51.0 dBA-.Leq(h). The noise measurement and analyses locations
are shown on the aerial photographs in Appendix F for both viable BUILD alternatives.
The traffic noise analysis indicates that the residential areas in Mussel Shoals, La
Conchita, and City of Carpinteria within the project area will be impacted after project
completion under all alternatives [i.e. the noise level will approach or exceed FHWA
Noise Abatement Criteria (NAC)]. Since traffic noise impacts have been identified, noise
abatement has been considered for the impacted receivers. As stated in 23 CFR 772 and
in the Department’s Protocol, noise abatement has only been considered where noise
impacts are predicted and where frequent human use occurs and where a lowered noise
level would be of benefit. For all impacted receptors, noise abatement has been evaluated
for preliminary acoustical feasibility (noise reduction of 5 dBA or more) and
reasonableness (cost effective).
Environmental Consequences
NO BUILD Alternative
Under the NO BUILD Alternative, existing conditions would remain and no impacts to
noise or vibration due to construction would occur.
BUILD Alternatives
Existing noise levels were recorded at 24 locations and modeled at 4 locations that
represented the noise sensitive areas along U.S. 101 in Ventura and Santa Barbara
Counties within the project limits. The existing noise levels recorded at various
residences/park ranged between 48 and 68 dBA-Leq(h). Soundwalls have been
recommended along the northbound and southbound sides of the U.S. 101 freeway. It
must be noted that the proposed location, length, noise reduction, and number of
benefited residences of each soundwall are the same for both BUILD alternatives.
Calculations based on preliminary design data indicate that the recommended barriers
would reduce future noise levels from 5 to 9 decibels (dBA) for approximately 136
residences under BUILD alternatives. The total reasonable cost allowance for the
recommended soundwalls is $7,048,000 for both BUILD alternatives. The total length of
the recommended barriers for both BUILD alternatives is 7,514 feet and minimum
heights would be 10 or 12 feet depending on location. If, during the final design,
conditions have changed substantially, then the recommended noise abatement measures
in this report may also change. The final decision for noise barrier construction will be
made upon completion of the project design and the public involvement process.
The locations where predicted traffic noise levels approach/exceed the Noise Abatement
Criteria of 67 dBA-Leq(h) were recorded for Activity Category B. The Activity Category
170 IS/EA VEN-SB US101 HOV Project