Sub-problem 4d: Further Consideration of the Northbound Right Turn

What HCM procedure might be employed to consider the operations of this location? The ramps and ramp junctions procedure (Chapter 25) will be considered in order to explore an alternative approach to assessing the performance of the northbound right-turn movement. In using this procedure, we would evaluate LOS on the basis of the thresholds shown in Exhibit 3-33.

In order to analyze the intersection as a merge area, though, we must first find a better way to analyze the capacity for this movement. Ideally, we would like to eliminate the movement from consideration within the more standard intersection analysis. Before we do that, we must satisfy ourselves that it will not experience capacity problems.

The HCM does not prescribe an explicit procedure for evaluating at-grade intersections with merge area characteristics. Therefore, we must develop an approximate estimation of performance using one of the available procedures. We have already tried the HCM procedure for TWSC analysis and have not been able to justify the elimination of the movement based on the v/c ratio. On the other hand, we must view the TWSC procedure as pessimistic because of the design of the merge area.