sidra intersection software complements highway capacity manual (hcm edition 6) as an advanced intersection analysis tool which offers various extensions on the capabilities of the hcm. the highway capacity manual version of sidra intersection has options for us customary and metric units. the roundabout capacity model for single-lane and multi-lane roundabouts based on research on us roundabouts as described in hcm edition 6, chapter 22 is integrated into the software. the hcm edition 6 roundabout capacity model is a lane-based model which is suitable for the extensions implemented in sidra intersection.