Rubberized open-graded asphalt on Phoenix freeways cut tyre-pavement noise at the source by an average of 8.7 dBA when new, then gave back about 0.5 dB every year after (ADOT and FHWA, Arizona Quiet Pavement Pilot Program Comprehensive Report 2018). That shape, a large opening gain followed by steady decay, runs through almost every dataset in this roundup. On the Paris ring road, a thin porous layer cut source noise by about 7.5 dB(A) three months after paving (Bruitparif 2018), while road traffic still exposes 92 million Europeans to more than 55 dB Lden, a weighted day-evening-night average (EEA, Environmental noise in Europe 2025). We aggregated data from the US Federal Highway Administration, the European Environment Agency, Rijkswaterstaat, Bruitparif, the Danish Road Directorate and Danish EPA, the Bavarian Environment Agency, NZ Transport Agency and recent acoustics conference papers. Barriers block sound on its way to the listener (see our outdoor noise barrier statistics); this roundup measures the other strategy, cutting the noise where the tyre meets the road.
TL;DR
- Phoenix rubberized asphalt: 8.7 dBA lower tyre-pavement noise when new, then about +0.5 dB per year (ADOT and FHWA Comprehensive Report 2018).
- 92 million people in Europe are exposed to road traffic noise above 55 dB Lden (EEA, Environmental noise in Europe 2025).
- For cars, rolling noise exceeds engine noise from about 30 to 40 km/h (Bavarian Environment Agency, LfU).
- Dutch single-layer porous asphalt (ZOAB) is about 3 dB quieter than dense asphalt, and durable ZOAB lasts 11 years on the truck-heavy right lane versus 17 years on the left lane (Rijkswaterstaat).
- A Danish thin SMA 6 XLN surface measured about 4.7 dB quieter at 50 km/h (Danish EPA, XLN-asfalt report 2024).
- Paris ring road: about 7.5 dB(A) source reduction three months after paving, but only 2.2 to 4.3 dB(A) at building facades (Bruitparif 2018).
- 51% of measures in urban noise action plans act at the source (ETC/ATNI Report 8/2019).
- US federal rules (23 CFR 772) do not allow pavement as a noise abatement measure (FHWA memo HEP-16-015).
- A6 motorway near Paris: EUR 3.5 million invested, EUR 61 million in avoided social costs, a benefit-cost ratio of 17 (Bruitparif 2023).
- Long-term monitoring studies of porous asphalt report decay of 0.5 to 1.3 dB(A) per year (Ramos et al., EAA Forum Acusticum 2026).
1. Why the Tyre-Road Contact Is the Target
The case for quiet pavement starts with physics, not policy. For cars, rolling noise from the tyre-road contact already exceeds engine noise from about 30 to 40 km/h (Bavarian Environment Agency, LfU). That means a quieter engine fixes very little on a ring road or motorway: above city-street speeds, the surface and the tyre set the noise level. Trucks are different, with tyre-road noise dominating only above about 60 km/h (Danish EPA, XLN-asfalt report 2024), so in slow urban traffic their engines still matter.
The exposure numbers explain why European cities keep reaching for the asphalt first. Road traffic exposes far more people than rail, and it dwarfs the 2.6 million people exposed to aircraft noise above the same threshold (EEA 2025; for the airport side see our aircraft noise exposure statistics). In the EEA indicator on noise exposure, night-time road noise alone reaches tens of millions of people.
| Metric | Value | Source |
|---|---|---|
| People in Europe exposed to road traffic noise above 55 dB Lden (day-evening-night average) | 92 million | EEA, Environmental noise in Europe 2025 |
| People in Europe exposed to rail noise above 55 dB Lden, for comparison with road | 18 million | EEA, Environmental noise in Europe 2025 |
| People affected by night-time road noise in Europe | around 57 million | EEA, Exposure of Europe’s population to noise indicator 2025 |
| People in EU-27 cities exposed to harmful urban road traffic noise | about 67 million | EEA, Exposure of Europe’s population to noise indicator 2025 |
| Speed from which rolling noise exceeds engine noise, cars | about 30 to 40 km/h | LfU Bayern, road surface noise page |
| Speed above which tyre-road noise dominates, trucks | about 60 km/h | Danish EPA, XLN-asfalt report 2024 |
| Share of measures in urban noise action plans that act at the source | 51% | ETC/ATNI Report 8/2019, Noise Action Plans |
| Noise action plans analysed in that review | 272 | ETC/ATNI Report 8/2019, Noise Action Plans |
Context note: the ETC/ATNI review of noise action plans found that renewing road surfaces or replacing rough pavements with smooth asphalt is the most used measure in urban areas, while on major roads the split flips: 40% of measures act on the propagation path (barriers and similar) and 38% at the source. The tyre itself is the other half of the contact: under EU tyre labelling Regulation 2020/740, applied since 1 May 2021, the quietest of three noise classes requires a tyre to measure at least 3 dB below the legal limit value.
2. Initial Noise Reduction by Surface Type
The opening gain depends heavily on how much open space the surface has and how many layers it uses. Dutch two-layer porous asphalt was measured up to 9 dB quieter than conventional dense-graded asphalt, against 1 to 3 dB for thin layers (FHWA, Quiet Pavement Systems in Europe scan). The pores work two ways: they let air escape from the tread instead of being trapped and squeezed under the tread (the noise source called air pumping), and they absorb part of the sound that is produced.
Scale matters for reading these figures. The Danish EPA XLN report describes 3 dB as a small but audible change and 5 dB as a clear change. So the jump from single-layer to two-layer porous asphalt is roughly the jump from “audible” to “clear”. The US numbers look smaller because the California study reports a median across many in-service sections of different ages, not the best new section. Most measurements here use the CPX method (close-proximity: microphones mounted right next to a test tyre on a trailer) or OBSI (on-board sound intensity, a probe near the tyre on a test car); for other ways engineers pin down where a noise comes from, see our acoustic camera statistics.
| Metric | Value | Source |
|---|---|---|
| Single-layer porous asphalt (ZOAB) vs dense asphalt, Dutch motorways | about 3 dB quieter | Rijkswaterstaat, ZOAB page |
| Two-layer ZOAB vs durable single-layer ZOAB | about 2 dB quieter | Rijkswaterstaat, ZOAB page |
| Porous asphalt vs conventional dense asphalt, typical initial range in the literature | 3 to 6 dB(A) | Ramos et al., EAA Forum Acusticum 2026 |
| Two-layer porous asphalt vs conventional dense-graded asphalt, Netherlands | up to 9 dB quieter | FHWA, Quiet Pavement Systems in Europe scan |
| Two-layer open-porous asphalt when new, Bavaria | more than 7 dB(A) | LfU Bayern |
| Open-graded asphalt (OGAC) vs dense-graded asphalt, California median across sections | about 2 dB(A) | UC Pavement Research Center, UCD-ITS-RR-08-50 (2008) |
| Rubberized open-graded asphalt (RAC-O) vs dense-graded asphalt, California median | about 3 dB(A) | UC Pavement Research Center, UCD-ITS-RR-08-50 (2008) |
| Danish SMA 6 XLN thin surface at 50 km/h vs the Nord2000 reference | about 4.7 dB | Danish EPA, XLN-asfalt report 2024 |
Context note: the same 2026 literature review in a Brisa motorway network study gives 7 to 8 dB(A) for double-layer porous systems, 2 to 4 dB(A) for thin asphalt layers and 1 to 3 dB(A) for SMA (stone mastic asphalt, a dense but coarse-textured mix). Most recent available data for the California and European-scan figures: 2008, and a scan page last updated in 2014.
3. Field Results on Real Roads: Phoenix and Paris
Field projects confirm the large opening gains but expose a gap between the source and the bedroom window. On Phoenix freeways, rubberized asphalt cut noise beside the freeway by an average of 9.1 dBA at first, but only 5.2 dBA in the residential neighbourhoods behind it (ADOT and FHWA, Arizona Quiet Pavement Pilot Program Comprehensive Report 2018). Paris shows the same thinning: about 7.5 dB(A) at the central median, 2.2 to 4.3 dB(A) at building facades (Bruitparif 2018). Other roads, engines and reflections fill in what the pavement removes.
Speed is the second filter. On three 50 km/h Paris streets, the best rolling-noise result was only -1.3 dB(A), short of the project target (EU LIFE Cool and Low Noise Asphalt project). That fits section 1: at city speeds, a larger share of the noise does not come from the tyre at all.
| Metric | Value | Source |
|---|---|---|
| Phoenix rubberized asphalt (ARFC), tyre-pavement noise at the source, average initial change | -8.7 dBA | ADOT and FHWA, FHWA-AZ-18-577-2 (2018) |
| Phoenix ARFC, noise directly beside the freeway, average initial change | -9.1 dBA | ADOT and FHWA, FHWA-AZ-18-577-2 (2018) |
| Phoenix ARFC, noise in nearby residential neighbourhoods, average initial change | -5.2 dBA | ADOT and FHWA, FHWA-AZ-18-577-2 (2018) |
| Paris ring road, average source reduction at the central median three months after paving | about 7.5 dB(A) | Bruitparif 2018, low-noise surface monitoring |
| Paris ring road, average reduction at residential building facades three months after paving | 2.2 to 4.3 dB(A) | Bruitparif 2018, low-noise surface monitoring |
| A4 and A6 motorways near Paris, LAeq 24h reduction with surfaces 3 to 6 months old | about 5 to 8.5 dB(A) | Bruitparif 2018, low-noise surface monitoring |
| Paris 50 km/h streets, best rolling-noise (CPX) reduction vs reference pavement, BBphon+ | -1.3 dB(A) | EU LIFE Cool and Low Noise Asphalt (LIFE16 ENV/FR/000384) |
| Paris 50 km/h streets, best ambient-noise reduction vs reference pavement, SMAphon | -2.8 dB(A) | EU LIFE Cool and Low Noise Asphalt (LIFE16 ENV/FR/000384) |
Context note: the ring road carries over 1.2 million vehicles per day, and even after resurfacing, night-time thresholds were still exceeded by 2 to 6 dB(A) at the facade stations. The Paris LIFE trial ran from 1 July 2017 to 30 June 2023 with a total eligible budget of EUR 2,256,418, of which EUR 1,353,207 came from the EU (project page). Most recent available data for the ring road: 2018.
4. Acoustic Decay: How Fast the Benefit Fades
Every quiet surface gets louder; the only question is how fast. Published decay rates span from 0.2 dB per year on Dutch ZOAB to about 1.0 dB(A) per year in the Danish rule of thumb for two-layer porous asphalt, a five-fold spread (1.0 divided by 0.2). Clogging fills the pores, and ravelling (stones working loose from the surface) changes the texture, so both mechanisms of the noise reduction weaken at once.
The Paris ring road rows in the table show how uneven the decay can be across lanes of the same road: lane 3 of the outer ring lost more than half of its reduction between 2012 and 2017 (from 10.1 to 4.6 dB(A)). New Zealand’s experience is milder: about 2 dB(A) lost over 8 to 10 years on high-speed roads (NZ Transport Agency Research Report 626).
| Metric | Value | Source |
|---|---|---|
| Phoenix ARFC, average noise increase after the initial reduction | about +0.5 dB per year | ADOT and FHWA, FHWA-AZ-18-577-2 (2018) |
| Paris ring road central median, degradation trend from 2014 onward | about +0.75 dB(A) per year | Bruitparif 2018, low-noise surface monitoring |
| Paris ring road, outer ring BBTM 0/4 surface, lane 3 reduction in 2012 vs 2017 | -10.1 dB(A) vs -4.6 dB(A) | Bruitparif 2018, low-noise surface monitoring |
| Dutch ZOAB, average loss of noise reduction after construction | 0.2 dB per year (±0.1 dB) | MNP, Evaluatie geluideigenschappen hoofdwegennet 2007 |
| Danish rule of thumb, two-layer porous asphalt | about 1.0 dB(A) per year (±0.3 dB(A)) | Danish Road Institute, Technical Note 45 (2006) |
| Danish drainage asphalt (8 mm, over 22% voids), reduction at year 0 vs year 7 | -3.2 dB vs -0.9 dB | FHWA, Quiet Pavement Systems in Europe scan |
| New Zealand standard porous asphalt at 80 to 100 km/h | about 2 dB(A) lost over 8 to 10 years | NZ Transport Agency, Research Report 626 (2017) |
| Porous asphalt, range reported by most long-term monitoring studies | 0.5 to 1.3 dB(A) per year | Ramos et al., EAA Forum Acusticum 2026 |
Context note: the Danish example is the sharpest warning in the table. A surface that started more than 3 dB quieter kept less than 1 dB of that benefit after seven years. Most recent available data for the Danish and Dutch rates: Danish Road Institute Technical Note 45 (2006) and MNP (2007).
5. Lifespan, Clogging and Maintenance
Acoustic life and structural life are two different clocks, and trucks wind both faster. Durable ZOAB lasts an average of 11 years on the right lane, where heavy goods vehicles drive, against 17 years on the left lane (Rijkswaterstaat). Six extra years on the lightly loaded lane is the clearest sign that heavy wheels, not weather alone, set the replacement date.
Maintenance can buy back part of the lost decibels, but not all of them. A German experiment summarised by the Danish Road Institute lost about 1 dB per year to clogging and regained about 0.5 dB per year through cleaning. Italy, one of the earliest large-scale adopters, built its porous mixes with very high void content and got close to, but not quite, the life of dense asphalt.
| Metric | Value | Source |
|---|---|---|
| Durable ZOAB average service life, right lane (heavier truck traffic) | 11 years | Rijkswaterstaat, ZOAB page |
| Durable ZOAB average service life, left lane | 17 years | Rijkswaterstaat, ZOAB page |
| Minimum air voids specified for Italian porous mixes (most built at about 30%) | 23% | FHWA, Quiet Pavement Systems in Europe scan |
| Share of the Italian Autostrade network surfaced with porous asphalt by end of 2003 | about 35% (1,868 km) | FHWA, Quiet Pavement Systems in Europe scan |
| Life of properly built Italian porous mixes as a share of quality dense-graded mixes | about 80 to 90% | FHWA, Quiet Pavement Systems in Europe scan |
| German experiment: noise reduction lost to clogging vs regained by cleaning | about 1 dB per year lost vs 0.5 dB per year regained | Danish Road Institute, Technical Note 45 (2006) |
| Bavarian A9 two-layer porous test section, age at replacement in 2013 | 8 years | LfU Bayern |
Context note: on a Danish city street at 50 km/h, two-layer porous asphalt was cleaned twice a year and still reached a structural life of only about 8 years, with the reduction falling from 5 to 6 dB to about 2 dB at the end (Danish Road Institute, Technical Note 45). Most recent available data for Italy: the network share describes the end of 2003.
6. Policy Credit, Costs and Benefit-Cost Ratios
The US and Europe read the same decay curves and reach opposite conclusions. US federal rules do not allow pavement type or surface texture as a noise abatement measure, because the reduction declines as the pavement ages (FHWA guidance memo HEP-16-015). The FHWA Traffic Noise Model, mandatory for federally aided highway projects, keeps a national average pavement type for predictions (FHWA Pavement Effects Implementation Study). European agencies, by contrast, count the decibels and cost the health damage they avoid.
The Dutch case shows why the credit matters. The national calculation method assumed 4.0 dB(A) for ZOAB, but measurements averaged 2.8 dB(A), so modelled noise maps understated exposure. The French A6 case shows why some agencies accept the decay anyway: even a benefit expected to vanish after about nine years paid back many times over (Bruitparif cost-benefit analysis 2023).
| Metric | Value | Source |
|---|---|---|
| US federal position on pavement as a noise abatement measure | not allowed under 23 CFR 772 | FHWA, memo HEP-16-015 |
| Noise reduction credit Arizona applied for rubberized asphalt in its pilot | 4 dB | FHWA, memo HEP-16-015 |
| Life-cycle window FHWA said a new Arizona benefit proposal may cover | somewhere in the range of 12 to 15 years | FHWA, memo HEP-16-015 |
| Dutch ZOAB reduction: assumed in the national calculation method vs measured average | 4.0 dB(A) vs 2.8 dB(A) (±0.8 dB(A), 95% confidence interval) | MNP, Evaluatie geluideigenschappen hoofdwegennet 2007 |
| Dwellings along Dutch national roads above 65 dB Lden if ZOAB delivers 3 dB | nearly 13,000 (±3,000) | MNP, Evaluatie geluideigenschappen hoofdwegennet 2007 |
| A6 motorway low-noise surface: investment vs avoided social costs | EUR 3.5 million vs EUR 61 million | Bruitparif 2023, cost-benefit analysis |
| A6 motorway low-noise surface, benefit-cost ratio | 17 | Bruitparif 2023, cost-benefit analysis |
| Cost of environmental noise in Europe | at least EUR 100 billion per year (about 0.6% of GDP) | EEA, Environmental noise in Europe 2025 |
Context note: on the A6, the number of residents exposed fell by 51% one year after paving and by 41% three years later, and the annual social cost of the noise fell from EUR 21 million to EUR 8.6 million (Bruitparif 2023). The FHWA memo also notes that no other agency had requested a Quiet Pavement Pilot Program since Arizona in 2003. The Dutch MNP figures are the most recent available data in this format (2007).
Summary: Porous Asphalt Quiet Pavement Noise Reduction by the Numbers
| Metric | Value | Source |
|---|---|---|
| Phoenix rubberized asphalt, tyre-pavement noise at the source: initial change, then yearly increase | -8.7 dBA, then about +0.5 dB per year | ADOT and FHWA 2018 |
| People in Europe exposed to road noise above 55 dB Lden | 92 million | EEA 2025 |
| Cost of environmental noise in Europe | at least EUR 100 billion per year | EEA 2025 |
| Share of measures in urban noise action plans that act at the source | 51% | ETC/ATNI 2019 |
| Speed from which rolling noise exceeds engine noise, cars | about 30 to 40 km/h | LfU Bayern |
| Double-layer porous systems, typical initial reduction in the literature | 7 to 8 dB(A) | Ramos et al., EAA 2026 |
| Thin layers | 1 to 3 dB | FHWA Europe scan |
| Rubberized open-graded vs dense-graded asphalt, California median | about 3 dB(A) | UC Pavement Research Center 2008 |
| Danish SMA 6 XLN at 50 km/h | about 4.7 dB | Danish EPA 2024 |
| Paris ring road, source reduction three months after paving | about 7.5 dB(A) | Bruitparif 2018 |
| Paris 50 km/h streets, best rolling-noise reduction | -1.3 dB(A) | EU LIFE Cool and Low Noise Asphalt |
| Danish rule of thumb for two-layer porous asphalt decay | about 1.0 dB(A) per year | Danish Road Institute 2006 |
| New Zealand porous asphalt decay | about 2 dB(A) over 8 to 10 years | NZ Transport Agency 2017 |
| Porous asphalt decay in long-term monitoring studies | 0.5 to 1.3 dB(A) per year | Ramos et al., EAA 2026 |
| Durable ZOAB service life, right lane vs left lane | 11 vs 17 years | Rijkswaterstaat |
| Dutch ZOAB reduction assumed in the calculation method vs measured | 4.0 vs 2.8 dB(A) | MNP 2007 |
| US federal position on pavement as a noise abatement measure | not allowed under 23 CFR 772 | FHWA memo HEP-16-015 |
| A6 motorway benefit-cost ratio | 17 | Bruitparif 2023 |
Methodology and Sources
- EEA, Environmental noise in Europe 2025: road, rail and aircraft exposure, cost of noise.
- EEA, Exposure of Europe’s population to noise (indicator, published 3 October 2025): night-time and urban road exposure from the 2022 noise mapping round.
- ETC/ATNI Report 8/2019, Noise Action Plans: Managing Exposure to Noise in Europe: measure types across 272 action plans.
- CINEA, Low noise road surfaces factsheet (October 2024): background on road surfaces as a widely reported urban mitigation measure.
- Regulation (EU) 2020/740 on tyre labelling: external rolling noise classes.
- LfU Bayern, road surface noise: two-layer and single-layer porous asphalt in Bavaria, rolling vs engine noise.
- Rijkswaterstaat, ZOAB: Dutch porous asphalt reductions and service life.
- MNP (now PBL), Evaluatie geluideigenschappen hoofdwegennet, van Beek and Hooghwerff 2007: assumed vs measured ZOAB reduction and decay.
- FHWA, Quiet Pavement Systems in Europe scan, Chapter Two: Dutch, Danish and Italian experience.
- FHWA, Guidance on Pavement as a Noise Abatement Measure, memo HEP-16-015: US federal policy and the Arizona pilot.
- FHWA, Pavement Effects Implementation Study: average pavement type in the Traffic Noise Model.
- ADOT and FHWA, Arizona Quiet Pavement Pilot Program: Comprehensive Report, FHWA-AZ-18-577-2 (2018): 10 years of Phoenix freeway measurements.
- UC Pavement Research Center for Caltrans, UCD-ITS-RR-08-50 (2008): California asphalt surface types, first- and second-year results.
- Bruitparif, Monitoring the acoustic performance of low-noise road surfaces (2018): Paris ring road and A4/A6.
- Bruitparif, Cost-benefit analysis of using low noise pavements in urban areas (EAA Forum Acusticum 2023): A6 cost-benefit.
- EU LIFE, Cool and Low Noise Asphalt (LIFE16 ENV/FR/000384): Paris 50 km/h street trial.
- Danish Road Institute, Technical Note 45, Noise reducing pavements: evaluation workshop (2006): decay rules of thumb, cleaning, structural life.
- Danish EPA (Miljostyrelsen), XLN-asfalt report, MUDP 2019-7107 (June 2024): Copenhagen thin-layer results.
- NZ Transport Agency, Research Report 626 (2017): long-term acoustic performance of standard porous asphalt.
- Ramos et al., Acoustic performance of road pavements on the Brisa motorway network, EAA Forum Acusticum 2026: literature ranges for initial reduction and decay.
- Data watch: the EEA gives two road exposure figures, 92 million above 55 dB Lden in the Environmental noise in Europe 2025 report and approximately 89 million in its October 2025 indicator page; we use 92 million as the headline and note the gap. The EEA 2025 report carries a March 2026 corrigendum on health outcomes, so we did not quote its premature-death or disease estimates. Much of the core decay evidence is older than three years (Danish Road Institute 2006, MNP 2007, UC Pavement Research Center 2008, Bruitparif 2018), and the Brisa 2026 paper is a preliminary, non-peer-reviewed conference contribution that also contains an internal inconsistency on which section aged fastest. Measurement methods differ (CPX, OBSI, roadside and facade microphones), so dB values from different studies should not be compared one to one. Bruitparif flags a possible bias in its Paris ring road series, because the 2012 to 2014 and 2014 to 2017 periods used different measuring equipment. Monitoring of the Paris LIFE streets continues after the project for a 10-year socio-economic evaluation, and Bruitparif projected the A6 benefit to be fully lost around 2026, so updated figures are expected.
Last updated: October 18, 2026. We update this roundup quarterly, and the next refresh is expected when Bruitparif publishes its next A6 and Paris low-noise pavement monitoring results.