The purpose of an impact threshold curve is to provide one tool to help determine whether the “secondary” or unintentional impacts of Neighborhood Traffic Management Program (NTMP) projects are acceptable. These impacts are frequently in the form of increased traffic on adjacent, non-project, Local Service streets. Impact limitations are expressed as a curve because the level of impact that is considered acceptable will vary, depending on the characteristics of the street being impacted by the NTMP project.
Among the benefits of employing an impact threshold curve are:
a) residents of adjacent non-project streets are provided with some assurance that traffic problems on one Local Service street will not be solved by simply shifting the problem to other Local Service streets;b) the curve can be translated into a table where the impact limit on any given street can be quickly and easily identified; andc) the impact curve provides a quantifiable and objective standard for measuring the success or failure of a project.