The current trend worldwide is less focused on reducing road traffic noise. This is in strong contrast to the severe impact of traffic noise to the general health and quality of life. A more holistic and combined strategy is needed. Current international rules and regulations regarding vehicles and tyres are not sufficient to reduce traffic noise levels in an effective way. Calculations show that these regulations will only yield a reduction of approximately 1.5 dB in Lden levels for urban traffic. Additional measures need to be implemented. By combining optimized tyres and road surfaces, a noise reduction of 4â–“6 dB can be achieved. Such tyres are currently being developed for electric and hybrid-electric vehicles. In addition to noise reduction, these tyres have less rolling resistance that can reduce vehicle energy consumption up to 15% on normal road surfaces. However, there are several obstacles still to be removed, such as the effectiveness of the EU tyre labeling system, and the implementation and durability of low-noise road surfaces. These challenges are discussed in the article.

Measures for the improvement of acoustic conditions in the vicinity of roads include the construction of pavement structures with low-noise surfaces with optimal macrotexture and the highest possible sound absorption coefficient. Laboratory evaluation of acoustic properties of a designed asphalt mixture before its placement in the pavement is a good solution. Currently, the most popular method for the determination of the sound absorption coefficient of various construction materials under laboratory conditions is the Kundt’s tube test. Sound absorption coefficient can also be assessed based on field and laboratory measurements performed using a Spectronics ACUPAVE System. Other parameters characterising the acoustic properties of road pavement courses include air void content and water drainability or permeability. The article presents an analysis of results of sound absorption coefficient obtained using a Spectronics ACUPAVE System and water drainability and permeability of poroelastic mixtures obtained both in laboratory and on test sections, in relation to air void content and grading of the mixtures. It was established that poroelastic mixtures containing an aggregate of maximum particle size of 5 mm are characterised by better acoustic properties than mixtures with a maximum aggregate particle size of 8 mm. Changes of crumb rubber aggregate grading and bitumen type (within the tested range of values) as well as the addition of lime have shown no evident influence on the sound absorption coefficient. Noise level values at the speed of 30 km/h according to the CPX method were measured as well. Relationships between sound absorption coefficient, water drainability/permeability, and air void content were determined. The performed analyses confirmed that Spectronics ACUPAVE System may be applied for evaluation of acoustic properties of asphalt mixtures in laboratory conditions, but further research is needed to reduce the uncertainty of the results.

This article presents the development process of designing and testing poroelastic pavement based on highly polymer-modified bitumen. Poroelastic wearing course was composed of mineral and rubber aggregate mixed with highly polymer-modified bitumen, in contrast to previous trials, during which polyurethane resins were mainly used as binder, which led to several serious technological problems concerning difficult production, insufficient bonding to the base layer, and unsatisfactory durability. The laboratory testing phase was aimed at finding the proper composition of the poroelastic mixture that would ensure required internal shear strength and proper bonding of the poroelastic layer with the base layer. After selecting several promising poroelastic mixture compositions, field test sections were constructed and tested in terms of noise reduction, rolling resistance and interlayer bonding. Despite the very good acoustic properties of the constructed poroelastic wearing course, it was not possible to solve the problem of its insufficient durability. Still, the second major issue of poroelastic pavements that concerns premature debonding of the poroelastic layer from the base layer was completely solved. Experience gained during the implementation of the described research will be the basis for further attempts to develop a successive poroelastic mixture in the future.

Double-layer porous asphalt concrete (DPAC) surfaces are generally considered to be the acoustically most effective low noise road surfaces ready for implementation. While DPAC used on highways in warm climates may have an average life of around 8 years, in Scandinavia with severe winter climate DPAC usually survive only about 3 years; partly due to wear of studded tyres. An ongoing project in Sweden, applying DPAC and single-layer porous asphalt (PAC), the latter consisting of the top layer of the DPAC, on motorway E4 in Jönköping-Huskvarna, has revealed interesting performance. Initial noise reduction was 7.5 dB(A) compared to a set of reference surfaces (conventional SMA 0/16). Amazingly, after one year of operation this noise reduction is unchanged. Most interesting is that the noise reduction difference between the single-layer and double-layer PAC is approx. 5 dB(A). Since the single-layer PAC is identical to the 30 mm thick top layer in the DPAC (although 5-8 mm thicker), it follows that 2/3 of the noise reduction is due to the bottom layer of the DPAC; i.e. what lies approx. 35-40 mm below the top surface. The paper will discuss the effect of the bottom layer on the overall acoustical efficiency of the DPAC.