Office of Industrial Hygiene

Requirements for Determining and Mitigating
Traffic Noise Impacts to Residential Structures

Roadway Classification: All roadways must be classified into one of the following categories as defined in the County's General Plan: "Secondary", "Major", "Arterial", "Urban Arterial", "Expressway", "Freeway", and "Specific Plan Road". For future reference the Riverside County Integrated Project (RCIP)/ General Plan can be accessed using http://www.rcip.org/general_plan_toc.html. The areas will be listed under AREA PLANS VOLUME 1 or 2. Click on area to be looked at. Under the section title “List of Figures” found near the bottom of the page, click on "Circulation" for the most current roadway classifications.
Roadway Traffic Volume: All roadways must be modeled using Average Daily Trip (ADT) level "C" design capacities (also known as future build-out daily traffic volumes) as quoted County of Riverside General Plan, Chapter 4, Page C-11 "Link Volume Capacities/ Level of Service for Riverside County Roadways" revised March 2001. Or the page can be found on the Internet at http://www.rcip.org/Documents/general_plan/gen_plan/fig_04_02.pdf, or in the case of freeways, contact CALTRANS for future ADT.

Required vehicle mix (MANDATORY)
i) Freeways: Vehicle mix information must be obtained from CALTRANS.
ii) Roadways designated as "major", "arterial" highways or "expressways":

VEHICLE	OVERALL %	DAY % (7AM-7PM)	EVENING % (7PM-10PM)	NIGHT % (10PM-7AM)
Auto	92	69.5	12.9	9.6
Medium Truck	3	1.44	0.06	1.5
Heavy Truck	5	2.4	0.1	2.5

iii) Roadways designated as "secondary", "collectors" or smaller.

VEHICLE	OVERALL %	DAY % (7AM-7PM)	EVENING % (7PM-10PM)	NIGHT % (10PM-7AM)
Auto	97.4	73.6	13.6	10.22
Medium Truck	1.84	0.9	0.04	0.9
Heavy Truck	0.74	0.35	0.04	0.35

Traffic Speed: For County roads assume an average traffic speed of 40 MPH. For freeways, contact CALTRANS and use what speed they recommend.
Terrain conditions for modeling noise propagation: Assume "hard site" conditions in determining noise propagation (no more than 3 dB of attenuation per doubling of distance between source and receiver).
Noise attenuation attributed to standard residential architecture: It is assumed that standard residential design (with windows closed) will provide no more than 20 dB (A) of attenuation. Additional mitigation must be demonstrated via modeling.
Receiver placement for modeling exterior noise levels (unmitigated): Noise levels must be estimated at the exterior face of the nearest residence at an elevation of five feet above the finished pad.
Receiver placement for noise barrier design:
i) Set back: Barrier calculations shall be based on a hypothetical outdoor receiver located ten (10) feet behind the intervening noise barrier.
ii) Receiver height: Initial calculations shall be based on a receiver height of five (5) feet above the ground. If these calculations result in a barrier less than or equal to six (6) feet in height, no further barrier calculations are necessary and this shall be selected as the required wall height. However, if the resulting barrier height is calculated to be greater than six feet, it shall be re-calculated using a receiver height of three (3) feet. The resulting re-calculated wall height shall be then selected as the required wall height.
Receiver placement for architectural-based (indoor) noise mitigation - first floor: First floor interior noise level predictions are to be calculated assuming a hypothetical receiver is located in the center of the room nearest the noise source and elevated 5 feet above the pad (finished floor).
Receiver placement for architectural-based noise mitigation-second floor: Second floor interior noise level predictions are to be calculated assuming a hypothetical receiver is located in the center of the room nearest the noise source and elevated 14 feet above the pad (or 5 feet above the second story finished floor).

NOISE REPORT FORMAT AND REQUIRED SUBMITTALS: The noise Consultants findings and recommendations must be submitted for review, and receive approval from, the Office of Industrial Hygiene. The resulting report must incorporate the requirements above and, at a minimum, contain the following information: a) a clear description of the proposed project; b) the identity and characterization of all acoustically significant roadways; c) a discussion of analytical methodology and parameters used for noise modeling; d) information obtained from applying requirements 6-10 (above); e) a discussion of mitigation (if necessary) including a clear diagram illustrating noise barrier placement; f) a printed copy of computer input/output (if available).

In addition to the report, Industrial Hygiene must be provided with the following depending on the design stage of the project. The first item that must be provided is a scaled map (blue-line) of the project. This map must clearly illustrate lot boundaries and the relative location of all acoustically significant roadways. Topographical elevations for lots and roadway centerlines must be included. Second, if architectural-based mitigation is necessary, and if the project has progressed to the point where plans for the homes have been drawn, copies must be provided (floor plans and exterior elevation drawings). Additionally, an updated blue-line showing exact pad location and finished floor elevation must be included.