Highway Projects

Frequenty Asked Questions

Route 85 Noise Mitigation Project

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Route 85 Noise Mitigation Project

Question: How did the Route 85 Noise Mitigation Project originate?

Answer: Route 85 was constructed as part of 1984 Measure A program and opened to traffic in 1994. Noise studies were conducted as part of the environmental approval process and noise mitigation measures were implemented. Post-construction noise analysis indicated that in general, the mitigation measures implemented satisfied Federal Highway Administration (FHWA) standards, Caltrans standards, and criteria established by the Traffic Authority for the 1984 Measure A program. However, residents along the west valley freeway corridor were not satisfied with the mitigation measures that had been implemented.

In 1996, the voters of Santa Clara County passed Measure A for highway and transit improvements. The Route 85 Noise Mitigation Project was not listed in the original 1996 Measure A advisory list of projects; instead, a median safety barrier project on Route 85 was included. By the time the Base Case 1996 Measure B Transportation Improvement Program (MBTIP) plan was adopted by the County in 1999, Caltrans had funded and completed the median safety barrier project with state funds. After conducting public input to develop the MBTIP, the County Board of Supervisors included the Noise Mitigation Project in the Base Case MBTIP.

Question: What are the various methods identified for noise mitigation?

Answer: In a 1998 Caltrans study, four methods were identified that were expected to reduce noise in the corridor by at least 3 decibels, the minimum level detectable to the human ear. These four methods were: reduce speeds by 10 mph; resurface existing pavement with open-grade asphalt; increase noise barrier heights; and place acoustically absorptive material on vertical wall surfaces.

Question: Why do texture-grinding (micro-grinding)?

Answer: Diamond-grinding of concrete pavement is a standard Caltrans pavement rehabilitation strategy to smooth the riding surface of concrete pavement that still has good structural qualities. Previous studies suggest grinding pavement can reduce noise generated from concrete pavement similar to the pavement on Route 85. In addition, studies show that the higher frequencies of noise, which are troubling to the human ear, are expected to be reduced by grinding.

Question : Why did VTA conduct a texture-grinding test project?

Answer : VTA conducted a test project in 2003 on a section of Route 85 to assess the potential of texture-grinding to reduce tire noise. The test section was located just north of Prospect Road area and extended southerly for less than one mile. Grinding operations lasted approximately two months. Crews monitored noise levels in the freeway right-of-way and on surface streets both before and after the grinding operations.

The test project indicated that texture-grinding the freeway pavement reduced overall noise, but it was less than the 3 dBA threshold that is perceptible to the human ear. However, the study determined the grinding caused a downward shift in the tonal characteristics of the sound and decibel reductions at frequencies that are easily heard by humans. Based on comments from the community, the combined effect has been a perceived reduction in noise.

Question: What is texture-grinding?

Answer: Texture-grinding (micro-grinding) is a type of pavement grinding in which machines with parallel saw-wheels grind away roadway surface bumps and rough spots, leaving a corduroy-like surface with a pattern of narrow, longitudinal grooves while retaining safe skid resistance.

Question: How does the cost of texture-grinding compare with the cost of asphalt concrete overlay?

Answer: VTA evaluated two types of asphalt concrete overlay as possible alternatives for reducing noise on Route 85: an open-graded asphalt concrete overlay and a rubberized open-graded asphalt concrete overlay.

VTA estimates that the initial costs for texture-grinding lies between the costs of the two asphalt overlay options. However, studies show that the noise benefit of an open-graded asphalt concrete pavement disappear after five to seven years, requiring replacing of the surface to maintain the same level of noise reduction.

Over a period of thirty-five years, the life cycle cost of the asphalt overlay is almost twice that of concrete grinding.

Question: What can we expect once this section of roadway is "texture-ground?"

Answer: The pavement surface will have a corduroy appearance after the grinding is completed. The pavement markings will be replaced to the original conditions.

Question: What are the hours of construction?

Answer: To minimize traffic impacts, the work will only occur at night. Partial lane closures on weekdays will normally be scheduled between 8:00 p.m. to 5:00 a.m. Partial lane closures on Saturdays may end at 8:00 a.m. Full freeway closures, if necessary, will be scheduled for 11:00 p.m. to 5:00 a.m.

Question: Why is the work being done at night?

Answer: Highway 85 is a heavily traveled freeway with high traffic volumes during daytime. To increase safety for the traveling public and the construction workers and to minimize impact to the traveling public the work will be done at night.

Question: Will the work require freeway closures and detours of traffic onto local streets?

Answer: Freeway closures will be necessary. Vehicles will be detoured onto local streets. Detour signs will be posted to properly direct the traffic.

Answer: Texture-grinding will generate noise levels at a level approximately 10% higher than freeway traffic.

Question: How can we contact VTA for more information on the project?