HCM Chapter 22

Roundabouts

Estimate entry capacities, control delay, queues, and level of service for each entry lane and for the roundabout as a whole.

The compute engine reproduces the published HCM worked examples for this chapter, including right-turn bypass lanes and the pedestrian entry adjustment. Verify results independently before relying on them in engineering work, and please report discrepancies on GitHub.

Roundabout

Circulation is counterclockwise; entries yield at the dashed line. Hover the legend to highlight an entry's movements, and in the 2D view the movement volumes can be edited directly on the diagram.

NB
SB
EB
WB

Circulation is counterclockwise and entries yield at the dashed line. Volume boxes are U-turn / left / through / right. A dashed bypass yields at its exit leg; a solid one merges without yielding. Animated vehicles are an illustration weighted by the entered volumes; after a run they slow and bunch with each approach's LOS. Not a simulation.

Northbound (NB) Entry

Demand and geometry for the south leg entry.

veh/h
veh/h
veh/h
veh/h
%

Applies to two-lane entries only.

p/h

Southbound (SB) Entry

Demand and geometry for the north leg entry.

veh/h
veh/h
veh/h
veh/h
%

Applies to two-lane entries only.

p/h

Eastbound (EB) Entry

Demand and geometry for the west leg entry.

veh/h
veh/h
veh/h
veh/h
%

Applies to two-lane entries only.

p/h

Westbound (WB) Entry

Demand and geometry for the east leg entry.

veh/h
veh/h
veh/h
veh/h
%

Applies to two-lane entries only.

p/h

Traffic

Peaking characteristics shared by all entries.

Leave blank if the demand values are already peak 15-min flow rates.

h

Outputs

Results populate after pressing Calculate.

Entry LaneFlow Rate (veh/h)Capacity (veh/h)v/cDelay (s/veh)LOS95% Queue (veh)
Intersection Delay (s/veh):

Intersection LOS: