Intersection Capacity Utilization

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. 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." 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 all 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 insure 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.

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 a different criteria for the rankings. In the 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. In short, the ICU method makes the traffic capacity design a much easier and simpler task.