This project investigated the potential of a layer of rubber-modified asphalt concrete (RMAC) under track ballast to improve the durability and reduce the deformation, vibration, and noise of track structures for high-speed rail (See Figure 1). Preliminary studies indicate that the damping ratio of rubber-modified asphalt concrete is 611% compared with 23% for compacted soil and 34% for conventional asphalt concrete. In addition, it has stiffness two to three orders of magnitude higher than typical compacted soil. Based on these findings, RMAC has the potential to significantly reduce the pressure on soil subgrade and reduce the vibration from passing trains to the surrounding environment. The project deliverables include specifications, performance assessments, and cost estimates for use by the  railroad industry to determine whether and how such installations should be made in the track structure.

The final report for this IDEA project can be found at:
https://onlinepubs.trb.org/onlinepubs/archive/studies/idea/finalreports/highspeedrail/hsr-40final_report.pdf.