Reliability Performance Measure Methodology


Reliability categories are determined by comparing the Buffer Time Index and average speed.  I-15 is segmented into 1-mile segments between Payson and Brigham City as well as in Southern Utah during the PM Peak Hour.

Reliability Score

The Reliability Score is determined by the percentage of Reliably Fast 1-mile segments.  Reliably Slow and Unreliable segments get a score of 0. The freeway segment values are weighted by their VMT.

Normalized Reliability Score

The Normalized Reliability Score is determined by dividing the Reliability Score by the target of 85%.  The maximum Normalized Reliability Score is 100.

Reliability Table