12.2.4.4 Level of Service
12.2.4.4 Level of Service
LOS is the letter grade assignment (A-F) of roundabout. It is based on control delay caused by a roundabout entry and is assumed to be LOS F if V/C is greater than 1.0. While the LOS A is the most favorable, scores A through D are typically acceptable ranges for LOS. Refer to HCM 7th Edition Chapter 22 for a step-by-step guide on performing manual calculations of LOS for motorized vehicles at roundabouts. SIDRA, Junctions and Synchro determine LOS automatically, while Vissim and SimTraffic can calculate LOS using control delay. The unsignalized LOS thresholds, referred to in HCM 7th Edition Chapter 22, as shown in , apply to roundabout yield control.
Control Delay (s/veh) | LOS by Volume-to-Capacity Ratio* | |
|---|---|---|
v/c≤1.0 | v/c>1.0 | |
0-10 | A | F |
> 10-15 | B | F |
> 15-25 | C | F |
> 25-35 | D | F |
> 35-50 | E | F |
> 50 | F | F |
Note: *For approaches and intersection wide assessment, LOS is defined solely by control delay