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Subproblem 6a - Page 2 of 3

ID# C306A02

Sub-problem 6a: Feasibility of Conversion to a Roundabout

Step 2: Results

Exhibit 3-42. Junction Conflict Points for a 3-legged Roundabout

The following steps are included in the HCM roundabout analysis procedure:

  1. Define the layout, identify the junctions at which conflicts occur and determine the traffic volumes entering at each junction. Since this is a three legged intersection, the junctions will be configured as shown in the box at the right

  2. Determine the conflicting (circulating) volume opposing the entry at each junction. If the circulating flow exceeds 1,200 vph, this procedure should not be used unless field data have been collected for the critical gap and follow-up time. 

  3. Determine the capacity of the entry lanes using the same equation that was given in the chapter for TWSC potential capacity. The critical gaps and follow up times are adjusted downward to reflect the fact that a roundabout entrance is generally designed to facilitate the entry of traffic into the circulatory roadway.

  4. Assess the general performance of the roundabout on the basis of the v/c ratio.

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