Calculation of National Highway System performance measures.

(a) The NHS Performance measures in § 490.507 shall be calculated in accordance with this section by State DOTs and MPOs to carry out the Interstate System and non-Interstate NHS performance-related requirements of this part, and by FHWA to make the significant progress determinations specified in § 490.109 and to report on system performance. (b) The Interstate Travel Time Reliability measure specified in § 490.507(a)(1) shall be computed to the nearest tenth of a percent as follows: Where: R = total number of Interstate System reporting segments that are exhibiting an LOTTR below 1.50 during all of the time periods identified in § 490.511(b)(1)(i) through (iv); I = Interstate System reporting segment “i”; SL i = length, to the nearest thousandth of a mile, of Interstate System reporting segment “i”; AV i = total annual traffic volume to the nearest single vehicle, of the Interstate System reporting segment “i”; J = geographic area in which the reporting segment “i” is located where a unique occupancy factor has been determined; OF i = occupancy factor for vehicles on the NHS within a specified geographic area within the State/Metropolitan planning area; and T = total number of Interstate System reporting segments. (c) The Non-Interstate Travel Time Reliability measure specified in § 490.507(a)(2) shall be computed to the nearest tenth of a percent as follows: Where: R = total number of non-Interstate NHS reporting segments that are exhibiting an LOTTR below 1.50 during all of the time periods identified in § 490.511(b)(1)(i) through (iv); i = non-Interstate NHS reporting segment “i”; SL i = length, to the nearest thousandth of a mile, of non-Interstate NHS reporting segment “i”; AV i = total annual traffic volume to the nearest 1 vehicle, of the Interstate System reporting segment “i”; j = geographic area in which the reporting segment “i” is located where a unique occupancy factor has been determined; OF j = occupancy factor for vehicles on the NHS within a specified geographic area within the State/Metropolitan planning area; and T = total number of non-Interstate NHS reporting segments. [82 FR 6031, Jan. 18, 2017, as amended at 83 FR 24936, May 31, 2018; 88 FR 85393, Dec. 7, 2023; 90 FR 16466, Apr. 18, 2025]