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May 22, 2017 Page 10 Table A-1 - Level of Service vs. Control Delay - Signalized and Unsignalized Intersections (TWSC, AWSC & Roundabouts) TWSC, AWSC & Roundabouts Signalized Intersections LOS by Volume to Capacity Ratio (≤ 1)* Control Delay per Vehicle (Seconds) LOS by Volume to Capacity Ratio (≤ 1)* Control Delay per Vehicle (Seconds) A ≤10 A ≤10 B >10 and ≤15 B >10 and ≤20 C >15 and ≤25 C >20 and ≤35 D >25 and ≤35 D >35 and ≤55 E >35 and ≤50 E >55 and ≤80 F >50 F >80 Per the 2010 Highway Capacity Manual, published by the Transportation Research Board. * NOTE: When LOS by Volume to Capacity Ratio >1.00, LOS is F. The acceptable Level of Service threshold for a particular movement at an intersection depends on both the priority assigned to that movement and its traffic volume. In general, the higher the priority and the higher the traffic volume, the more stringent the acceptable threshold will be. For example, the acceptable threshold for a high- priority/high-volume rural movement might be C, while LOS F on a low-priority/low- volume urban movement might be appropriate. For two-way stop-controlled intersections, a key measure of operational effectiveness is the side street LOS. Since the mainline does not have to stop, the majority of delay is attributed to the side-street/minor approaches. Long delays and poor LOS can sometimes result on the side street, even if the overall intersection is functioning well, making it a valuable design criterion. As the side-street/minor approach delay approaches and exceeds 60 seconds per vehicle, drivers may divert to another route or become impatient and accept gaps in the mainline traffic that are less than acceptable/safe gaps resulting in the potential for traffic safety concerns. Therefore, depending on priority and traffic volume, acceptable side-street LOS can range from D to F. Side streets can operate at LOS F without the intersection warranting a change in traffic control. A final fundamental component of operational analyses is a study of vehicular queuing, as defined the line of vehicles waiting to pass through an intersection. An intersection can operate with an acceptable Level of Service, but if queues from the intersection extend back to block entrances to turn lanes or accesses to adjacent land uses, unsafe operating conditions could result.