27 CAR § 95-410. Sensitivity analysis

(a)(1) Because all traffic forecasts are subject to uncertainty, there is inherent risk in any decisions based on the operational analysis (and other analyses as well) of alternatives. (2) Traffic forecasts for a new interchange may be realized in ten (10) years instead of twenty (20). (3) Also, changes in land use, such as a new high-traffic shopping center immediately nearby, can have significant impacts on the adequate operation of an interchange. (b)(1) Realizing that even a slight increase or change in traffic demand could result in nearly saturated or oversaturated operations, proposed alternatives must be tested under a variety of traffic demand scenarios, commonly referred to as a sensitivity analysis. (2) It is recommended that at least a ten-percent increase in traffic demand should be included in the sensitivity analysis. (3) Other factors, such as potential changes in land use and upstream capacity restraints, should be considered on a case-by-case basis. (c)(1) The main purpose of the sensitivity analysis is to identify any risks associated with any alternatives that should be considered by decision makers. (2)(A) For example, the sensitivity analysis may show that a ten-percent increase in traffic demand may increase the length of the ninety-fifth percentile back-of-queue for a ramp terminal intersection such that it would exceed the storage space provided between it and a frontage road intersection. (B) In this example, the risk of such overflow of queuing may be unacceptable because of the potential costs of relocating the frontage road intersection once development occurs.