Percentage of Person-Miles Traveled on the Interstate System with Reliable Travel Time
Unreliable travel times on these critical roads requires their users to budget extra time to ensure they arrive at their destinations on time. This increases commutes, limits movement of goods, and otherwise reduces quality of life and economic efficiency. The Level of Travel Time Reliability (LOTTR) is defined as the ratio of the longer travel times (80th percentile) to a “normal” travel time (50th percentile). The measure is the percentage of person-miles traveled on the region’s Interstate system that meet this definition of reliability. Using person-miles rather than vehicle-miles gives equal weight to all individuals using the roads. This measure is also a federally required performance measure under MAP-21.
Operations programs that, for example, improve incident management or implement advanced traffic management, could result in short term improvement despite the lack of new projects on the system. Regionally significant projects, travel demand management, and vehicle technology are expected to improve reliability over the long term, despite increasing population. This improvement could be limited by an increase of severe weather events. A 2050 target of 90 percent was set based on the results of CMAP’s own travel modeling analyses of strategies to improve reliability. Full reliability can never be achieved due to uncontrollable factors like weather.
2025: 70.8 percent or more of person-miles traveled on the Interstate system are reliable
2050: 90.0 percent or more of person-miles traveled on the Interstate system are reliable