1. What effect does HFST have on road noise?

• In general, roads treated with HFST will be less noisy than transversely tined concrete pavement, chip seals, and certain dense-graded asphalt pavements. While HFST does increase the mean texture depth (MTD) and mean profile depth (MPD), the relationship (for all types of pavement surfaces) between MPD and noise level is extremely weak, and it is even worse for MTD. Therefore, it is not a valid conclusion that higher texture depth will lead to more noise.
• Some noise reductions and pavement color changes may be perceived by drivers, especially on curves, which may tend to cause a reduction in average speeds. Additional research in this area is needed to substantiate or refute this question.
• Overall, since most HFST installations only span from the point of curvature (beginning of the curve) to the point of tangency (end of the curve), the difference in the sound level produced by driving over the HFST will only last for a few seconds, and then the vehicle will be back on the regular pavement surface.
• Tire-pavement noise was measured by The Transtec Group on two HFST sections (one in Kansas and one in Montana) approximately 1 year after they were installed. The Kansas installation was on a dense-graded asphalt pavement and the Montana installation was over a chip seal. These were very limited tests, and further study of this issue should be performed to generate more reliable correlations; however, the findings indicate that HFST applied over the chip seal was slightly quieter (expressed as overall onboard sound intensity (OBSI) in A-weighted decibels (dBA)):
  • Chip seal: ˜104.4
  • HFST: ˜101.95

  For the HMA, HFST was slightly louder:

  • HMA: ˜98.75
  • HFST: ˜100.05

  Note: 3 dBA is essentially the minimum threshold for human-perceived change in noise level.

2. Bike groups have expressed concerns about the abrasiveness of HFST. How is this being addressed across the country?

3. What are some of the major environmental benefits for HFST?

• No physical reconstruction of road surface so no change in drainage patterns.
• No increase in impervious area footprint.
• Short construction timeframe results in less chance of environmental-related mishaps during construction.
• Installation eliminates complete road closure due to HFST’s capability of being applied one lane at a time, resulting in less pollution due to congestion and less traffic delay.
• Please refer to a case study highlighting a successful installation of HFST by Caltrans in an environmentally sensitive area: https://safety.fhwa.dot.gov/roadway_dept/pavement_friction/ case_studies_noteworthy_prac/nocal/