21-foot sound barriers approved along I-35 for Central Austin neighborhood

Sound barriers are typically installed when traffic sound levels reach 66 decibels or higher—roughly the volume of a normal conversation—or when future traffic is projected to double current noise levels, according to TxDOT documents. For comparison, a vacuum cleaner registers around 70 decibels, a whistle 80, and a blender 90.

According to Federal Highway Administration regulations, a noise wall should lower traffic sounds by about 5 decibels once it’s tall enough to block the direct view between the road and nearby homes. For every extra meter the wall is made taller after that, it can reduce noise by roughly another 1.5 decibels.

Some context

The work falls under the ongoing I-35 overhaul, which includes two new high-occupancy vehicle lanes in each direction, reconstructed east-west crossings and a new pedestrian bridge at Capital Plaza in this area. Construction is expected to wrap up in 2032.