Travel Time Reliability: Planning Time Index

Travel times vary greatly from day to day, and travelers remember those few bad days they suffered through unexpected delays. Travel time reliability measures the extent of this unexpected delay. Planning time index (PTI) represents the additional time that a traveler should budget to ensure on-time arrival 95% of the time. Different from on-time arrival, the higher the PTI, the worse the reliability is.

Different from on-time arrival, the higher the PTI, the worse the reliability is. In 2019, the PTI on Florida’s freeways during peak hour stayed at 1.53. The traveler needs to plan 15.3 minutes 95% of the time with a 1.53 PTI. The peak hour PTI went up from 1.48 in 2015 to 1.53 in 2019.

Methodology

Methodology: Travel Time Reliability: Planning Time Index

Planning Time Index (PTI) is defined as the ratio of the 95ᵗʰ percent peak period/hour travel time to the free flow travel time. This measure represents the additional time that a traveler should budget to ensure on-time arrival 95 percent of the time.

Calculation

`"Travel Time"_("95th percentile")/"Travel Time"_("free flow")`

Reporting Periods

  • Peak Hour
  • Peak Period
  • Daily
  • Yearly

Sources

FDOT - Traffic Characteristics Inventory
HERE Technologies - Travel Time Data