National Performance Management Research Data Set (NPMRDS)

Traffic data was obtained from NPMRDS for all federal aid routes in Utah.  Data used for the following three Federal Highway Administration (FHWA) performance measures includes average travel times for 15-minute intervals for each highway segment to be analyzed. More information about the NPMRDS data can be found here. 

System Reliability

Level of Travel Time Reliability (LOTTR) is defined as "the consistency or dependability of travel times from day to day or across different times of the day."  LOTTR is calculated 
The LOTTR is calculated for each roadway segment as a ratio of normal drive time compared to congested drive time. The established target for LOTTR is 1.5, where delayed drive time should not exceed 1.5 times the normal drive time. LOTTR is calculated for four time intervals, weekdays from 6am-10am, 10am-4pm, 4pm-8pm, and weekends from 6am-8pm.  If the LOTTR score for any of the time intervals exceeds 1.5, the segment is considered unreliable. 
Reliability is reported to FHWA in terms of Travel Time Reliability Measure (TTRM), which is a ratio of person-miles traveled that are reliable to total person-miles traveled. Travel Time Reliability measures are reported for Interstate and Non-Interstate segments of the National Highway System. Segment reports are further divided by Metropolitan Planning Organization (MPO) boundaries. More information regarding LOTTR and TTRM methodology is available by the FHWA

Interstate Person Miles

Non-Interstate NHS Person Miles


Freight Movement and Economic Vitality

Freight movement is assessed using a measure of travel delay just as system reliability was measures using Level of Travel Time Reliability (LOTTR). The LOTTR is calculated for each roadway segment as a ratio of normal drive time compared to congested drive time. The established target for LOTTR is 1.5, where delayed drive time should not exceed 1.5 times the normal drive time. LOTTR is calculated for four time intervals, weekdays from 6am-10am, 10am-4pm, 4pm-8pm, and weekends from 6am-8pm.  If the LOTTR score for any of the time intervals exceeds 1.5, the segment is considered unreliable. 
Reliability of freight movement is reported to FHWA in terms of Truck Travel Reliability TTTR, which is a ratio of truck miles traveled that are reliable to total truck miles traveled. Truck Travel Time Reliability measures are reported for Interstate and Non-Interstate segments of the National Highway System. Segment reports are further divided by Metropolitan Planning Organization (MPO) boundaries. More information regarding LOTTR and TTRM methodology is available by the FHWA

Interstate Truck Miles

Non-Interstate Truck Miles


Peak Hours Excessive Delay (PHED)

Excessive Delay is the amount of time spent in congested conditions at speeds lower than a normal delay threshold (60% of posted speed limit).
PHED was calculated using 2017 National Performance Management Research Data Set (NPMRDS) data from February - August, with peak hours being weekdays 6-10 am and 4-8 pm.
To calculate PHED four preceding calulations were made for each road segment (traffic message channel or TMC segmentation).
1. Calculate Excessive Delay Threshold Travel Time (EDTTT): the threshold above which a delay would occur.
          EDTTT = (segment length in miles / the greater of 60% speed limit or 20 mph) x 3,600
2. Calculate Road Segment Delay (RSD)
          RSD = travel time seconds of all vehicles - EDTTT
3. Calculate Excessive Delay in hours for the segment.
          Excessive Delay = RSD / 3,600          (If RSD < 0 than Excessive Delay = 0.)
4. Calculate Total Excessive Delay  in person-hours of delay for the eight months of data.
          Total Excessive Delay = (sum of each day's Excessive Delay)  x  (15-minute volume peak hours)  x  (average vehicle occupancy of 1.2)
The table below shows PHED for each MPO as the hours of delay per capita for the seven month period of data. The map shows road segments with relatively low, mid, or high delays during peak hour travel times.