§ 490.611 Calculation of Truck Travel Time Reliability metrics. ( a ) The State DOT shall calculate the TTTR Index metric (referred to as the TTTR metric) for each Interstate System reporting segment in accordance with the following: ( 1 ) A truck travel time data set shall be created from the travel time data set to be used to calculate the TTTR metric. This data set shall include, for each reporting segment, a ranked list of average truck travel times, to the nearest second, for 15 minute periods of a 24-hour period for an entire calendar year that: ( i ) Includes “AM Peak” travel times occurring between the hours of 6 a.m. and 10 a.m. for every weekday (Monday -Friday) from January 1st through December 31st of the same year;
( ii ) Includes “Mid Day” travel times occurring between the hours of 10 a.m. and 4 p.m. for every weekday (Monday-Friday) from January 1st through December 31st of the same year;
( iii ) Includes “PM Peak” travel times occurring between the hours of 4 p.m. and 8 p.m. for every weekday (Monday-Friday) from January 1st through December 31st of the same year;
( iv ) Includes “Overnight” travel times occurring between the hours of 8 p.m. and 6 a.m. for every day (Sunday-Saturday) from January 1st through December 31st of the same year; and
( v ) Includes “Weekend” travel times occurring between the hours of 6 a.m. and 8 p.m. for every weekend day (Saturday-Sunday) from January 1st through December 31st of the same year.
( 2 ) The Normal Truck Travel Time (50th percentile) shall be determined from each of the truck travel time data sets defined under paragraph (a)(1) of this section as the time in which 50 percent of the times in the data set are shorter in duration and 50 percent are longer in duration. The 95th percentile truck travel time shall be determined from each of the truck travel time data sets defined under paragraph (a)(1) of this section as the time in which 95 percent of the times in the data set are shorter in duration. Both the Normal and 95th percentile truck travel times can be determined by plotting the data on a travel time cumulative probability distribution graph or using the percentile functions available in spreadsheet and other analytical tools.
( 3 ) Five TTTR metrics shall be calculated for each reporting segment; one for each data set defined under paragraph (a)(1) of this section as the 95th percentile travel time divided by the Normal Truck Travel Time and rounded to the nearest hundredth.
( b ) Starting in 2018 and annually thereafter, State DOTs shall report the TTTR metrics, as defined in this section, in accordance with the HPMS Field Manual by June 15th of each year for the previous year's Freight Reliability measures. ( 1 ) All metrics shall be reported to HPMS by reporting segments. When the NPMRDS is used metrics shall be referenced by NPMRDS TMC(s) or HPMS section(s). If a State DOT elects to use, in part or in whole, the equivalent data set, all reporting segment shall be referenced by HPMS section(s).
( 2 ) The TTTR metric shall be reported to HPMS for each reporting segment (to the nearest hundredths) for each of the five time periods identified in paragraphs (a)(1)(i) through (v) of this section; the corresponding 95th percentile travel times (to the nearest second) and the corresponding normal (50th percentile) travel times (to the nearest second).