“As traffic congestion continues to worsen, the time required for a given trip becomes more unpredictable, and researchers now have a way to measure that degree of unreliability, introduced for the first time as part of the annual Urban Mobility Report (UMR), published by the Texas A&M Transportation Institute (TTI). The Planning Time Index (PTI), a measure of travel reliability, illustrates the amount of extra time needed to arrive on time for higher priority events, such as an airline departure, just-in-time shipments, medical appointments or especially important social commitments. If the PTI for a particular trip is 3.00, a traveler would allow 60 minutes for a trip that typically takes 20 minutes when few cars are on the road. Allowing for a PTI of 3.00 would ensure on-time arrival 19 out of 20 times.”
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