Nonrecurring congestion is measured by the the Planning Time Index (PTI), which is the ratio of the 95th percentile travel time relative to the free-flow (uncongested) travel time. PTI helps in understanding the impacts of nonrecurring congestion from crashes, weather, and special events. It approximates the extent to which a traveler should add extra time to their trip to ensure on-time arrival at their destination. A value of 1.0 indicates a person can expect free-flow speeds along their route. A 2.0 index value indicates a traveler should expect that the trip could be twice as long as free-flow conditions. PTI values from 2.0 to 3.0 are considered moderately unreliability and ones greater than 3.0 are highly unreliable.

The data comes from aggregated Global Positioning System probe data—data from mobile apps, connected vehicles, and commercial fleets—provided to the Probe Data Analytics (PDA) Suite by INRIX, a travel data technology company. The PDA Suite was created by a consortium of sponsors, including the Eastern Transportation Coalition and the University of Maryland.

PTI values by region, subregion, and county are grouped either as freeway facilities or local roads. Freeways are roadway segments classified as interstates, turnpikes, and expressways in the PDA Suite. Local roads are segments classified as U.S. routes, state routes, parkways, frontages, and others. The PDA Suite reports out weekday hourly averages in facility directions (northbound, southbound, eastbound, and westbound) by selected facility types and geographies. Data is also reported by time of day (TOD) an average of these hourly and directional values by facility type, within the following time periods:

Morning (AM): 6:00 AM–9:59 AM; Midday (MD): 10:00 AM–2:59 PM; Evening (PM): 3:00 PM–6:59 PM; Nighttime (NT): 7:00 PM–5:59 AM; and Daily: 12:00 AM–11:59 PM.

All values reflect an average weekday.