Table 2 provides a brief description of each LOS letter designation and an accompanying average delay per vehicle for both signalized and unsignalized intersections. The Highway Capacity Manual 2010 (HCM 2010) methodology was used in this study. This methodology has different quantitative evaluations for different types of intersections: for signalized and all-way stop controlled intersections, the LOS is provided for the overall intersection (weighted average of all approach delays); whereas only the worst approach delay is reported for two-way stop controlled intersections. Table 2: Level of Service Descriptions
Signalized Intersections Avg. Delay (Sec/Veh)
Unsignalized Intersections Avg. Delay (Sec/Veh)
LOS
Description
A Free Flow / Insignificant Delay Extremely favorable progression. Individual users are virtually unaffected by others in the traffic stream. Stable Operations / Minimum Delays Good progression. The presence of other users in the traffic stream becomes noticeable. Stable Operations / Acceptable Delays Fair progression. The operation of individual users is affected by interactions with others in the traffic stream Approaching Unstable Flows / Tolerable Delays Marginal progression. Operating conditions are noticeably more constrained. E Unstable Operations / Significant Delays Can Occur Poor progression. Operating conditions are at or near capacity. Forced, Unpredictable Flows / Excessive Delays Unacceptable progression with forced or breakdown of operating conditions. B C F D
< 10
< 10
> 10 to 20
> 10 to 15
> 20 to 35
> 15 to 25
> 35 to 55
> 25 to 35
> 55 to 80
> 35 to 50
> 80
> 50
Source: Fehr & Peers descriptions, based on 2010 Highway Capacity Manual , 2018.
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