Acoustic targets, panel types, structural loads and standards — a specification method for procurement teams and EPC contractors, aligned with JT/T 646-2025, GB/T 51335-2018 and HJ/T 90-2004.
Start from the project's required insertion loss (dB) at the receiver — not from a panel catalogue. Convert that target into the STC / Rw the panel must deliver, add an NRC ≥ 0.60 absorptive face where reflection matters, and size height and post spacing from the acoustic model and design wind load. Panels meeting Rw ≥ 26 dB (non-transparent) per JT/T 646-2025 satisfy the mainstream Chinese highway procurement baseline.
Every barrier specification starts upstream of the panel itself.
A noise barrier is bought to solve a measured problem: predicted traffic noise at a defined receiver exceeds the environmental limit. The difference between predicted level and the limit is the insertion loss the barrier must achieve at that receiver — commonly 5–15 dB for highway projects.
Insertion loss is not a panel property. It is the combined result of panel sound insulation, barrier height and length, the source–receiver geometry, and ground reflection. A panel with excellent STC can still deliver poor insertion loss if the barrier is too short or ends before the receiver.
Practical method: commission (or request) an acoustic report following HJ/T 90-2004 — Acoustic Design and Measurement Specification for Noise Barriers. The report should state the design insert-loss target and the required panel STC. Everything else in the specification flows from these two numbers.
The most consequential single decision — and the most often defaulted.
| Criterion | Absorptive (perforated + infill) | Reflective (solid metal) |
|---|---|---|
| Acoustic function | Absorbs incident sound; NRC typically 0.80–0.95 | Blocks and reflects sound back toward the source side |
| Best for | Urban corridors, dual receiver sides, opposite facades, noise-sensitive zones | Open terrain, single receiver side, lower-budget sections |
| Cost | Higher (perforation + rock-wool/glass-wool infill) | Lower |
| Maintenance | Drainage and infill protection must be detailed | Minimal — washdown surface |
| Standard benchmark | NRC ≥ 0.60 (JT/T 646-2025 for absorptive panels) | Rw ≥ 26 dB (JT/T 646-2025 for non-transparent panels) |
Rule of thumb: if a reflective barrier would bounce noise toward occupied buildings on the other side of the road, specify absorptive. Zhaobang standard panels reach NRC 0.80–0.95 and STC 25–35 dB depending on configuration.
Geometry does more for insertion loss than panel grade.
Height. The barrier must break the line of sight between source and receiver. Truck exhaust stacks sit roughly 2.5–3.5 m above the road, so panels 2.0–4.0 m high cover most highway cases; 5.0–6.0 m applies to elevated sections or highly sensitive receivers. Beyond full line-of-sight blockage, each extra metre of height buys progressively less dB.
Length. End-diffraction erodes performance near barrier ends. As a working rule, extend the barrier well past the first and last protected receiver — commonly 30–50 m beyond, or until the acoustic model confirms the target.
Post spacing. Standard modular panels suit 2.0–2.5 m post spacing; wider spacing raises panel wind load and deflection, narrower spacing raises steel quantity. Spacing is finalized together with the post section and foundation depth under the design wind load for the site.
Barriers fail structurally long before they fail acoustically.
The post–foundation system carries the full wind load on the panel area. Design it to GB/T 51335-2018 (Technical Standard for Noise Barrier Structures) using the site's return-period design wind speed, checking post bending, anchor bolts and foundation overturning.
Durability. Hot-dip galvanized steel posts and frames with powder-coated or PVDF aluminium panels cover most climates; coastal and de-icing-salt environments justify C5-class coating systems and 304/316 fasteners. Specify drainage details for absorptive panels so infill stays dry — waterlogged infill loses absorption and adds dead load.
For the full panel construction breakdown — infill materials, perforation patterns, fixing systems and finishes — see the noise barrier specifications reference page.
JT/T 646 (Highway Noise Barriers), issued by the Ministry of Transport of China and updated in 2025 across parts 646.1, 646.2 and 646.4, specifies a weighted sound reduction index Rw ≥ 26 dB for non-transparent panels and a noise reduction coefficient NRC ≥ 0.60 for absorptive panels, together with structural, safety and durability requirements. Zhaobang panels are specified to meet or exceed these thresholds.
Absorptive panels (perforated face over rock-wool or glass-wool infill) are recommended where the barrier faces another reflective surface, where buildings line both sides of the road, or where reflected noise would degrade conditions on the opposite side. Reflective panels are adequate for open terrain with a single receiver side and offer lower cost and simpler maintenance. A good traffic barrier combines a high-NRC absorptive face with enough mass to deliver a useful STC.
Barrier height is set by the acoustic model: the panel must break the line of sight between the source (truck exhaust stacks at roughly 2.5–3.5 m) and the receiver. Typical highway installations use 2.0–4.0 m above the road surface, extending to 6.0 m for sensitive receivers or elevated road sections. Increasing height improves insertion loss with diminishing returns once direct sound is fully diffracted around the top edge.
The post-foundation system must resist the design wind pressure for the site's return-period wind speed, applied to the full panel area including a shape/drag coefficient, plus check overturning and foundation bearing under that load. Structural design should follow GB/T 51335-2018 (Technical Standard for Noise Barrier Structures) and the local highway design wind code. Post spacing, panel thickness and foundation depth are all sized from this load case.