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On the last day of the scan team’s visit in Denmark, Professor Ulf Sandberg from Chalmers University of Technology in Gothenburg (Sweden), also affiliated with the Swedish National Road and Transport Institute, presented some of his research (see figure 17). Sandberg reported that in one of his projects, three approaches are being investigated for tire innovations for low noise emission:
The Danes also consider at least three ways of increasing the noise-reducing properties of porous pavement:
Figure 17. Photo from Professor Ulf Sandberg’s presentation.
(VINNOVA, Swedish Agency for Innovation Systems)
The Danes have evaluated the long-term noise-reduction performance of several mixes, including single- and double-layer porous mixes using small (5 mm), intermediate (8 mm), and large (11 mm) aggregates, and several performance-graded modified asphalts. They are also evaluating thin mixes similar to Novachip and microsurfacings using the same series of aggregates sizes.
In addition, one innovative quiet pavement technology being investigated is the poroelastic road surface (PERS). This surfacing is made mainly of rubber in prefabricated panels or rolls with a porosity of about 35 percent. Although the noise reduction is good, durability has been a challenge. For example, there have been problems with snowplows scarring the pavement. Conversely, studded tire resistance is good. Another innovative design is the use of interlocking blocks (concrete blocks with asphalt surface), which has exhibited a noise reduction of about 8 dB.
In response to the Noise Nuisance Act of 1979, the Dutch Ministry of Transport, Public Works, and Water Management and the Ministry of Environmental Affairs have initiated a sizeable IPG to reduce road noise. The program is charged with developing noise-reducing measurements. The goal of the program is to reduce traffic noise significantly, especially through the use of source-related measures. In addition, the program focuses on implementing or developing the technologies and products to a level of general application. The approach to the program is to investigate all possibilities of noise reduction by road surfaces, tires and vehicles, and enhanced noise barriers. Potential results include decreased dependence on barriers and increased use of source-related measures. Strategic aims include noise reduction, affordability, readiness for implementation, and source measures. Technical aims include noise reduction (5 dB), construction durability of 8 to 10 years, cost effectiveness (50 percent reduction compared to the road), and acoustic durability (4-dB lifetime average).
Technical clusters include silent vehicles and tires, silent roads, more efficient barriers, assessment measures, and knowledge infrastructure. The focus of the silent roads effort was the design and development of a new generation of silent roads. The expected noise reductions from this program (2003–2007) were 4 dB for road surfaces, 2 dB for tires and vehicles, and 2 dB for barriers, for a total of 8 dB. Table 5 outlines information still to be gained.
| Nonporous | Porous | |
|---|---|---|
| Car Tires | A lot is known | Some Knowledge |
| Truck Tires | Little Knowledge | Almost none |
Goals for new research:
The Dutch research program includes studies on truck tires in Germany, porous surfaces in the Netherlands, truck tires on porous surfaces, and development of hybrid models that account for truck tires on porous surfaces, as well as applications of these studies.
Perhaps the most innovative research being conducted in the Netherlands is the Roads to the Future (RTF) program, launched in 1996 to improve mobility. This program tries to envision 30 years into the future and develop concepts that will be important then. There are competitions to propose ideas, the most promising of which move toward construction of test sites. The program runs in 3-year cycles and is now in the third cycle, with 30 to 32 pilot projects completed. After a theme has been chosen (e.g., maintenance) the question becomes, “What will be crucial to maintenance 30 years in the future?” Respondents are asked what they expect or what they would envision, as opposed to what they think is likely. Incremental steps are then taken toward this long-term vision.
Road Surfaces of the Future occurred in the second RTF cycle. Roads had to be modular in construction and designed for a specific purpose. The phases for RTF include long-term perspective (large-scale pilot project), development of functional specifications, construction of a pilot project, and development of improved specifications.
An RTF test section has been constructed on A50. Its features include rapid construction and removal, functional design, major noise reduction (greater than 5 dB), high permeability comparable to PA, modular construction, and room for other functions (sensors, energy production, etc.).
The test sections include the following (see table 6):
| Pavement Type | Expected Noise Reduction, dB | Actual Noise Reduction, db |
|---|---|---|
| Very Silent Sound Module | 10 | 5 |
| Rollable Road | 8-10 | 6 |
| ModieSlab | 6-7 | 6-7 |
| Adhesive Road | 6-7 | 6 |
Figure 18.Test road for very silent sound module (Helmholtz resonator).
Other research programs include the following:
One of the more impressive test sections the team observed was a TLPA section on A28 (figure 19). The section includes eight different contractors’ mixes for TLPA. The pavement was exceptionally quiet and exhibited no splash/spray during an afternoon rain event. The team also visited an EAC test site with sections ranging from 4/8 mm to 11/16 mm. EAC is generally louder for passenger cars than dense-graded asphalt, but quieter for trucks.
Figure 19. Two-layer porous asphalt section on A28.
In France, the research program considers all aspects of noise—mitigation, emission, and reception at building facades. However, no formal process exists for implementing research. Contractors in France, as well as in most other European countries, are conducting product research on their own. This process seems to be well entrenched and works well as a public/private partnership.
Experimental pavements using resonant technology (euphonic and ecotechnical), originally used by the Romans 1,700 years ago to control low-frequency noise, are being studied under SIRUUS (see figure 20). In addition, experimental sections of synthetic aggregate mixes are being tested for noise mitigation. These synthetic mixes are composed of 12 percent by weight expanded clay that has been kiln dried. To date, more than 12 million square meters have been placed with an average –2-dB noise differential from the reference dense-graded mixes. Again, these mixes were first used because of their high skid-resistant properties, but later were later found to provide a noticeable reduction in tire-pavement noise.
Figure 20. The “euphonic road” in Italy.
Many of the SIRUUS pavement concepts are variations of the euphonic pavement, which consists of two layers of PA connected to a layer with Helmholtz resonators in either the third or fourth layer. Sometimes the third layer is a transition layer. The Helmholtz resonators are designed to absorb noise over the range 100 to 250 Hz. Compared to the reference pavement, these pavements typically are 2 to 4 dB better from 80 to 250 Hz, 8 to 14 dB better from 315 to 800 Hz, and 2 to 6 dB better from 800 to 5,000 Hz.
Several acoustic models are part of the SIRUUS project: tire noise generation, sound absorption, vehicle emissions, and structural behavior of silent pavements.
The United Kingdom’s HAPAS road surface influence parameter has categorized standard types of road surface (when new) in the following order of decreasing noise:
The road surface influence is based on SPB measurements of vehicle noise. A considerable amount of research effort has been put into developing a strategy for continuous monitoring using the CPX method (TRITON mobile research laboratory) and correlating these noise data with continuous measurements of surface texture made routinely to monitor skid resistance.
EAC and thin bituminous surfacings are found to be largely self-cleaning, but PAs clog up over a period of about 5 years. Research monitoring the noise performance of PA with 20- mm aggregate showed a 5-to-6-dB initial reduction and a 3-dB 8-year reduction in pass-by noise compared to a (positively textured) conventional HRA with 20-mm aggregate. Traffic noise increases on negatively textured surfaces immediately after rainfall. Traffic noise levels measured alongside both Masterpave (thin surfacing) and PA surfaces increased by 3.2 dBA and 3.5 dBA, respectively, when compared with measurements on dry surfaces, but there was no increase in the noise on adjacent HRA monitored for comparison.
The United Kingdom is involved in the European research and development partnership called Silenda Via (SILVIA, or Sustainable Road Surfaces for Traffic Noise Control). The objective of SILVIA is to provide decisionmakers with guidelines on the selection of sustainable road surfaces for noise reduction. Outputs will include a classification method, a cost/benefit analysis, sustainable solutions, integrated noise measurements, and ultimately overall guidance and advice on performance measures. Preliminary results of the SILVIA project are at www.trl.co.uk/silvia. A final report is due in 2006.
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