Travel Time Index (TTI)
The TTI measure helps to assess congestion by comparing the average travel time for a segment of road during the peak hour (7-8 AM, and 5-6 PM) to the free-flow travel time for the same segment. A TTI of 1.5 indicates that the travel time is, on average, 50 percent longer during the peak hour. For example, a trip that would take 20 minutes under free-flow conditions would take 30 minutes during the peak hour. It is normal and appropriate for TTI to increase during peak hours.
Scoring (Peak Hour TTI, 7-8 AM or 5-6 PM, whichever is greater, all weekdays in 2017)
High (1) = Greater than 1.5 (highly congested)
Medium (0.5) = 1.2 - 1.5 (moderately congested as expected at peak hour)
All of the measures to Reduce Congestion can combine to total a maximum of 2 points per link.
Source: INRIX, DVRPC.
Anticipated Growth in V/C using the DVRPC Travel Model
This measure indicates where congestion will likely increase in the future on a road segment during the peak hour (7-8 AM and 5-6 PM). It gives added weight to locations that are already moderately congested (V/C 0.5 or more) in the model base year (2015).
The analysis uses the 2015 and 2045 DVRPC travel model runs, the same as used for the Long-Range Plan (Connections 2045). It identifies potential future congested roadways using the 2045 socio-economic forecasts, and any projects approved for funding. This analysis indicates traffic congestion at the regional level, and is not intended to provide precise congestion by segment. Accuracy at the segment level is estimated at +/- 15%.
The 7-8 AM or 5-6 PM V/C ratio, whichever is greater, by segment in the 2015 and 2045 models are compared. Only segments with two or more times the range of accuracy (30%) are considered to have an increase in congestion.
The mapping reflects minor inaccuracies that can occur when transferring existing model data to GIS. Growth in congestion from this analysis is only suitable for regional planning purposes, not for engineering.
Scoring (Anticipated Growth in V/C in the 2015-2045 Peak-Period Travel Models, 7-8 AM or 5-6 PM, whichever was greater, all weekdays)
High (1) = 2015 V/C ratio of 0.5 or greater, and 30% or greater change in the peak period V/C ratio from 2015 to 2045
Medium (0.5) = 30% or greater change in the peak period V/C ratio from 2015 to 2045
All of the measures to Reduce Congestion can combine to total a maximum of 2 points per link.
Source: DVRPC.