Master Transportation Plan Task 4: Gap Analysis and Needs Network
based on usage (i.e., traffic movements) and performance (i.e., time). Replica 2023 was used to analyze all intersections. 3.4.2 Methodology Traffic Movement Counts for 2023 from Replica were used to identify the top 10 intersections in each of the 10 districts. Intersections with the highest total traffic movements were selected to be part of this list. This first subset provides the 100 top intersections ( Figure 15 ) in terms of usage. Therefore, improvements made over any of these intersections would likely have high benefits for travelers. The second filter applied was regarding performance, to identify the most critical intersections (i.e., highest usage, lowest performance). Performance was estimated using a representation of delay— Travel Time Index (TTI). Replica Quarter-Hour Speeds for 2023 was used to estimate this measure over all the approaching roadways for each of the 100 intersections, and TTI is estimated as: 𝑇𝑇𝑇𝑇𝑇𝑇 = 𝑡𝑡 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 𝑡𝑡 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 −𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 ≈ 𝑣𝑣 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 −𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 𝑣𝑣 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 1 Where, • 𝑡𝑡 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 is travel time in the peak periods. • 𝑡𝑡 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 −𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 is travel time at free flow. • 𝑣𝑣 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 is speed in the peak periods. Assumed as the lowest speed from AM and PM peaks. • 𝑣𝑣 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 −𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 is free flow speed. Assumed as the maximum speed across the day. • Peak periods are A.M. (6:30 A.M. to 9:00 A.M.) and P.M. (3:00 P.M. to 6:30 P.M.) per NCTCOG’s TDM definitions. TTI was derived for all legs of the intersection without considering slip ramps. To get a weighted average TTI per intersection, each leg was assigned a weight based on the facility type, considering orders of magnitude of traffic that different facilities can carry. Replica’s “category” labels were used as a proxy for this, and the weights are shown in Table 5 . Table 5. Weights per Roadway Category Category Weight Highway Trunk 10.0 Primary 5.0 Secondary 5.0 Tertiary 2.5 Trunk Link 1.25
1 Assuming the analysis is done for the same segment length.
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