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Intersection Capacity Utilization (ICU) method is a tool for measuring a roadway intersection's capacity. It is ideal for transportation planning applications such as roadway design, congestion management programs and traffic impact studies. It is not intended for traffic operations or signal timing design.〔("Monroe Avenue Corridor Study" ), ''SRF Associates'', April 2010, accessed December 9, 2010.〕 ICU is also defined as "the sum of the ratios of approach volume divided by approach capacity for each leg of intersection which controls overall traffic signal timing plus an allowance for clearance times." 〔Crommelin, R W ("Employing Intersection Capacity Utilization Values To Estimate Overall Level of Service" ), ''Transportation Research Board'', 2010, accessed December 8, 2010.〕 The ICU tells how much reserve capacity is available or how much the intersection is overcapacity. The ICU does not predict delay, but it can be used to predict how often an intersection will experience congestion. The method by which the ICU is used shows what the ICU is about. The ICU uses a grading system to rank the intersection that is being studied. This ranking system is known as the Level of Service (LOS) for the intersection. ICU is timing plan independent, yet has rules to ensure that minimum timing constraints are taken into account. This removes the choice of timing plan from the capacity results. The ICU can also be used on uncontrolled intersections to determine the capacity utilization if the intersection were to be signalized. The ICU is not intended for operations or signal timing design. The primary output from ICU is similar to the intersection volume to capacity ratio. Some of the benefits to using ICU over delay-based methods include greater accuracy, and a clear image of the intersection’s volume to capacity ratio.〔Husch, David ("Intersection Capacity Utilization" ), ''Trafficware'', 2003, accessed September 15, 2015.〕 ICU method has been subject to some competition from the Highway Capacity Manual (HCM). Both methods are used to determine the LOS of an intersection. However, each method has different criteria for the rankings. In transportation, each method is used for different types of projects. The review board of the ICU continue to make changes every year in order to incorporate all of the new criteria required. The ICU has not been designed for operations and signal timing design. Delay based methods and simulation such as HCM, Synchro, and SimTraffic should be used for operations and signal timing design.〔("Syncho 7" ), ''Trafficware'', 2010, accessed December 8, 2010.〕 In short, the ICU method makes the traffic capacity design a much easier and simpler task. == Methodology == The ICU methodology requires a specific set of data to be collected. The data needs to include volumes, number of lanes, saturated flow rates, signal timings, reference cycle length, and lost time for an intersection. The method sums the amount of time required to serve all movements at saturation for a given cycle length and divides by that reference cycle length. This method is similar to taking a sum of critical volume to saturation flow ratios (v/s), yet allows minimum timings to be considered. The ICU method uses the concept of the Level Of Service (LOS) where LOS reports on the amount of reserve capacity or capacity deficit. In order to calculate the LOS for the ICU method, the ICU for an intersection must be computed first.〔 ICU can be computed by: ICU = (max (tMin, v/si) * CL + tLi) / CL = Intersection Capacity Utilization CL = Reference Cycle Length tLi = Lost time for critical movement i v/si = volume to saturation flow rate, critical movement i tMin = minimum green time, critical movement i〔 Once the ICU is fully calculated for an intersection, the ICU LOS for that intersection can be calculated based on the following criteria: LOS A: If ICU is less than or equal to 55% B: If ICU is greater than 55% but less than 64% C: If ICU is greater than 64% but less than 73% D: If ICU is greater than 73% but less than 82% E: If ICU is greater than 82% but less than 91% F: If ICU is greater than 91% but less than 100% G: If ICU is greater than 100% but less than 109% H: If ICU is greater than 109%〔 This grading criteria shows some specific details about the specific intersection: A: Intersection has no congestion B: Intersection has very little congestion C: Intersection has no major congestion D: Intersection normally has no congestion E: Intersection is on the verge of congested conditions F: Intersection is over capacity and likely experiences congestion periods of 15 to 60 consecutive minutes. G: Intersection is 9% over capacity and experiences congestion periods of 60 to 120 consecutive minutes. H: The intersection is 9% or greater over capacity and could experience congestion periods of over 120 minutes per day.〔 Most industry standards require the ICU LOS to be E or better. This is not always easy to achieve and therefore much care is given to the signal timings and geometry in order to get the LOS to be better than E. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Intersection capacity utilization」の詳細全文を読む スポンサード リンク
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