System Performance Measures
The Performance Measures for System Performance are:
- Percent of reliable person-miles traveled on the Interstate
- Percent of reliable person-miles traveled on the non-Interstate NHS
- Freight movement on the Interstate by the percentage of Interstate system mileage
System performance measures assess the Travel Time Reliability (TTR) for all traffic on the NHS and the Truck Travel Time Reliability (TTTR) only for trucks on the Interstate system. TTR and TTTR conditions are calculated using the National Performance Management Research Data Set, commonly referred to as speed data. Speed data is divided into five time periods for each segment on the system: morning, midday, evening, overnight and weekends. Within these time periods, speed data is evaluated in 15 minute increments. The worst increment in the worst grouping is selected so that each segment in the system has one value per day of the year.