HCM for Roundabout Intersections

The Traffic Control table for the HCM 7^th Edition, HCM 6^th Edition and the HCM 2010 method for roundabouts is shown in the figure of the table below.

Table definitions are presented in the table below the figure HCM Traffic Control Table: HCM for Roundabout Intersections. Common parameters are described in a separate chapter (see section Common Parameters and Unknown Control Type).

Figure 16: HCM Traffic Control Table: HCM for Roundabout Intersections

Table 21: Traffic Control Parameters: Roundabouts - HCM for Roundabout Intersections

Parameter	Description	Units
Intersection Settings
Analyze Intersection?	A check box indicates this intersection will be included in the reports. Intersections, for which the flag is deactivated, are not exported to Vissim. This allows to export partial networks.
Analysis Period	Time period for the analysis, either 15 min, utilizing the peak 15-min flow multiplied by 4 assigned by the PHF, or 1 hr, ignoring the PHF.
Number of Conflicting Circulating Lanes	Number of lanes directly in conflict with the approach entry lanes.
Circulating Flow Rate	Number of vehicles circulating in the roundabout and passing in front of the entry approach, conflicting with the entry flow.	veh/h
Exiting Flow Rate	Number of vehicles exiting on the specific approach.	veh/h
Demand Flow Rate	Volumes represented as an hourly flow rate	veh/h
Adjusted Demand Flow Rate	Demand Flow Rate adjusted for heavy vehicles	veh/h
Lanes
Overwrite Calculated Critical Headway?	Checkbox to allow for overwriting of calculated critical headway value.
User-Defined Critical Headway	Value of critical headway, if defined by user	s
Overwrite Calculated Critical Follow-Up Time?	Checkbox to allow for overwriting of calculated critical follow-up time value.
User-Defined Critical Follow-Up Time	Value of critical follow-up time, if defined by user	s
A (intercept)	Capacity model intercept based on follow-up headway used for calibration
B (coefficient)	Capacity model coefficient based on critical and follow-up headway used for calibration
HV Adjustment Factor	Adjustment factor for heavy vehicles, based on heavy vehicle percentage input in volumes table.	veh/h
Entry flow rate	Approach entry flow rate by lane	veh/h
Capacity of Entry and Bypass Lanes	Total capacity of entry and bypass lanes by approach	veh/h
Pedestrian impedance	Capacity reduction factor to account for impedance of conflicting pedestrians
Capacity per Entry Lane	Entry capacity converted to vehicles per hour	veh/h
X, volume / capacity	Volume to capacity ratio per lane of entry
Movement, Approach, & Intersection Results
Average Lane Delay	Average control delay per lane of entry	s/veh
Lane LOS	Level-of-s2ervice per lane of entry
95th-Percentile Queue Length	95^th percentile queue length measured in number of vehicles per lane	veh
95th-Percentile Queue Length	95^th percentile queue length measured in feet per lane	ft
Approach Delay	Average control delay for the selected approach	s/veh
Approach LOS	Level-of-service for the selected approach
Intersection Delay	Intersection average control delay	s/veh
Intersection LOS	Intersection Level-of-service