There are three performance measures to assess the performance of the Interstate System and the performance of the non-Interstate NHS for the purpose of carrying out the National Highway Performance Program (referred to collectively as the NHS Performance measures).

(a) Two measures are used to assess reliability (referred to collectively as the Travel Time Reliability measures). They are:

(1) Percent of the person-miles traveled on the Interstate that are reliable (referred to as the Interstate Travel Time Reliability measure); and

(2) Percent of person-miles traveled on the non-Interstate NHS that are reliable (referred to as the Non-Interstate Travel Time Reliability measure).

(b) One measure is used to assess GHG emissions, which is the percent change in tailpipe CO2 emissions on the NHS compared to the reference year (referred to as the GHG measure).