Sub-problem 3b: Ramps

Discussion
What did we learn from this sub-problem? First, we learned what is involved in analyzing a ramp and where to find the methodologies you need. They’re not in one place but distributed among four HCM chapters: ramps, weaving sections, unsignalized intersections, and signalized intersections. We demonstrated a way to determine which methods you need to use when.

Second, we looked at the issue of checking the capacity of the ramp roadways themselves. We used the v/c ratio analysis technique in the ramps chapter of the HCM and determined that two of the ramps in the interchange are at or near capacity. Ideally, their curve radii should be larger or more lanes should be present.

Third, we studied the two merges that occur on Route 7 going westbound. The first is associated with the loop ramp coming from I-787 north. The second is related to the right-hand ramp coming from I-787 south. We noticed that the second ramp is difficult to analyze because the acceleration lane never ends. It continues on as a third lane on the freeway. We determined how to analyze the level of service with this in mind. We found that both ramps are adequate. We lengthened the acceleration lane on the first ramp to determine how to achieve LOS A, which also meant lengthening the ramp until it overlapped with the second on-ramp. We also discussed how the lane configuration might have to change for the second ramp and the repercussions from making those changes. We found that the pair of ramps could be made to work well, and the length of the ramp had an impact on performance.

Sub-problems 3c and 3d look at more complicated situations to show how complex ramp geometries should be handled.