Researched by Allan Bowditch, President, Engage Estero.

Introduction

Florida’s Department of Transportation (FDOT) has decided to expand I-75 from 6 lanes to 10 between Corkscrew Road to Immokalee Road. This expansion is likely to result in increased traffic noise. The FDOT will examine the potential impact of this expansion on adjacent communities. The option most likely to be chosen is that of barrier walls. The question is which type and product will be selected? Engage Estero considered it essential to explore the options.

This article aims to review the investigative research conducted by the Federal Highway Administration to evaluate the various products developed by companies to decrease the impact of traffic noise on major highways.

The way Sound Barrier Walls are Assessed

There are two key measures used when assessing the effect of sound barrier walls used along highways.

 

1. STC (Sound Transmission Class)

What it measures:

STC is a numerical rating of how well a material or barrier blocks airborne sound—especially speech and general traffic noise—through the barrier.

In noise barrier walls: The higher STC = better at stopping sound from passing through the wall. It measures transmission loss (sound energy that doesn’t pass through).

Example scale:

STC 25: Can hear normal speech through it.

STC 35–40: Loud speech is faint.

STC 45–55+: Ideal for highway sound barriers; truck and traffic noise are greatly reduced.

The typical range for highway noise walls that should be used is STC 30 to 45+, depending on material and thickness.

 

1. NRC (Noise Reduction Coefficient)

What it measures:

NRC is a number between 0 and 1 that represents how much sound is absorbed (not reflected) by a surface.

NRC 0.00 = Reflects all sound (like concrete).

NRC 1.00 = Absorbs all sound (like thick acoustic foam).

In noise barriers:

A higher NRC means less echo and reverberation. In urban or enclosed areas, or near residential zones, it is imperative to reduce reflected noise that is directed back toward homes.

Typical NRC values for noise walls:
Reflective barriers: NRC 0.05–0.15

Absorptive barriers: NRC 0.70 to 0.95+

 

Combined Use in Sound Walls

 

Wall Type	STC (Blocking) NRC (Absorbing)	Best Use Case
Concrete Panel	High (~35–40) Low (~0.10)	Great at blocking; reflects sound back
Absorptive Wall	High (~35–40) High (~0.85)	Blocks & absorbs—ideal for urban/high-density
Transparent Wall (e.g., acrylic)	Medium (~25–30)            Very Low	Maintains view/light; modest sound control

 

• In Summary:

STC = Blocks sound from passing through.

NRC = Absorbs sound to prevent echo/reflection.

For highway noise, the best barriers combine a high STC (≥35) and high NRC (≥0.80)—this blocks the sound from passing through and also prevents it from bouncing back into nearby areas.

Leading Companies & Brands for Highway Noise Barriers

1. Valmont SoundWall™ (North America)

Offers lightweight fiberglass‑composite reflective and absorptive panels designed for highway use.

STC Ratings: Reflective 28–35; Absorptive up to 37, with NRC ~0.95.

Offers Easy and fast installation with lightweight equipment, a 50-year lifespan, minimal maintenance, and UV/fire/corrosion resistance.

The Product is a recognized winner of the Federal Highway Administration (FHWA) Environmental Award for innovation.

1. Durisol Precast Noise Barriers (North America, including Canada)

Made from a lightweight cementitious composite with softwood shavings, high absorption (NRC 0.70–0.90), and STC ~38.

Panel heights of up to 43 ft and custom architectural finishes are available; the panels have a lifespan of over 40 years. Manufactured in Canada & U.S.; NPCA‑certified plants.

 

1. AIL Sound Walls (Canada / U.S.)

PVC-based noise walls (Tuf‑Barrier reflective and Silent Protector absorptive) filled with mineral wool.

1. Lightweight, weather‑proof, impervious to rot or rust; meets ASTM F3459‑21; STC ≈
2. Offers transparent acrylic options, aesthetic textures, and graffiti resistance.

 

In Summary

It is crucial to select absorptive barriers (e.g., Valmont absorptive, Durisol precast, AIL Silent Protector) to minimize echoes and sound reflection in nearby areas. These also help prevent the tunnel effect caused by reflective walls.

It is also essential to account for reflective walls in spaces with limited dimensions—some Valmont or AIL configurations require lower heights and a smaller footprint. For projects focused on sustainability or aesthetics, Durisol and AIL provide customization options with various textures, colors, transparent panels, and even green wall integration.

The best product overall is considered to be:

Valmont SoundWall™—durable, high acoustic performance, user-friendly install.

The best absorptive option is considered to be:

Durisol Precast Noise Barrier—excellent NRC, Canadian/U.S. made, visually flexible.

If you plan to attend the upcoming FDOT meeting, consider asking which product will be chosen and why based on the research conducted by the Federal Highway Administration.