From the city’s quiet zone information page:
The City of Austin submitted the Notice of Establishment (NOE) to the Federal Railroad Administration (FRA) for the railroad crossing of the Union Pacific Railroad at Duval Road on January 12, 2011. This Quiet Zone will be officially in effect on February 2, 2011 (21 days from January 12, 2011).
A quiet zone for this location means that trains will no longer sound their horns as they approach the crossing. This will reduce the noise exposure of homes near the tracks substantially.