The level of highway traffic noise depends on four factors:

  • Volume of traffic
  • Speed of traffic
  • Number of large trucks
  • Location of highway relative to the house

Noise is measured in decibels (dB(A)).

The INDOT Traffic Noise Policy establishes two criteria for identifying an impact resulting from a project:

  1. Identifying where future predicted noise levels would approach or exceed a set of Noise Abatement Criteria (NAC) established in the FHWA regulations. For outdoor uses in residential areas, the NAC is 67 decibels (dB(A)); INDOT defines “approaching the NAC” as within 1 dB (66 dB(A) for residential areas). Therefore, locations where future noise levels are predicted to be 66 dB(A) or higher are considered “impacted.”


2. Identifying locations where noise levels are expected to increase by 15 dB(A) or more over existing levels. There were no increases of 15 db(A) or more for the North Split project.

View FAQs about noise abatement
View supplemental FAQs about noise abatement
Learn about noise barriers
Learn about the noise abatement neighborhood meetings