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Sub-problem 5a - Page 2 of 7

ID# C205A02

Sub-problem 5a: I-87 Interchange - Merges and Diverges on the Freeway

Southbound-to-Westbound Off-Ramp
The southbound-to-westbound off-ramp has significant volumes in both the AM and PM peaks. We’re going to study the AM peak as the PM peak should be similar. In the AM Existing condition, the freeway volume upstream of the ramp is 3,751 vph and the ramp volume is 437 vph. The closest ramp is the downstream off-ramp, which has a volume of 314 vph. In the AM Without condition, those volumes become 3,841, 455, and 326 vph respectively; in the AM With condition, they are 3,851, 565, and 326.

Exhibit 2-54 shows how the ramp’s performance varies by case. You can click here to see the datasets. The LOS is always C, but the density within the influence area increases from 23.2 to 24.6 vehicles per lane per mile. The adjacent ramp is the downstream southbound-to-eastbound off-ramp.

Exhibit 2-54. I-87 Interchange Southbound-to-Westbound Off-Ramp
Case Density Speed LOS
AM Existing 23.2 54 C
AM Without 23.9 54 C
AM With 24.6 54 C

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