Definition
A Travel Time Index (TTI) is a measure of average conditions that indicates how much longer, on average, travel times are during congestion compared to during light traffic.

Example
A TTI of 1.60 means a trip that usually takes 10 minutes in light traffic could take up to an additional 6 minutes on average (60% longer than the free-flow travel time).

Formula

• TT_AVG = Average Travel Time
• TT_FF = Free Flow Travel Time

Definition
Speed is the average of the recorded speeds at different points along a segment during a given period of time. Volume is the average number of vehicles that traverse a given segment per hour.

Example
The average Speed at different points on I-95 Northbound at the 5:00 PM hour is 49 mph. The average Volume for the segment on I-95 Northbound, between NW 53 Street and Ives Dairy Road, at 5:00 PM is 1,272 vehicles per hour.

Definition
The Average Travel Time (TT_AVG) is the average time it takes to traverse a segment during a given period of time.

Example
The Average Travel Time it takes to travel I-95 Northbound from South of NW 53 Street to North of Ives Dairy Road during the 5:00 PM hour is 17.7 minutes.