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2049 Congestion Management Program <br />Appendix B -1 <br />guidelines in the ITE Trip Generation Manual and appropriate professional judgment are the <br />predominant techniques employed. To supplement the guidance available through ITE <br />documentation, local jurisdictions are encouraged to undertake additional studies to document <br />rates applicable within their jurisdiction. The determination of applicable rates should be <br />undertaken by experienced transportation engineering professionals with thorough <br />documentation of the methodology, data, and assumptions used. It is recommended that those <br />jurisdictions which do not currently allow these adjustments establish revised TIA procedures <br />incorporating this element. As with trip generation data, a central library would be desirable for <br />reporting of data and analyses performed locally related to determination of appropriate factors. <br />Trip Distribution and Assignment <br />Several appropriate: distribution and assignment_ techniques are used in Grange County, <br />depending on the size of the development and the duration of buildout, Manual and computer <br />modeling approaches are used as appropriate. Manual methods based on the best socio- economic <br />information available to the agency and applicant should be acceptable except when a <br />development's size makes a modeling approach more appropriate. Sources of this information <br />include demographic surveys, market analyses, and previous studies. <br />Radius of Development Influence <br />There are numerous ways to identify the study area to be evaluated in a TIA. These include both <br />qualitative and quantitative approaches. One of the most effective ways is through the <br />determination of the quantity of project traffic on CMP roadway links compared to a selected <br />level of impact. The foal of a quantitative approach is to be sure that all elements of the CMP <br />network are addressed in a comparable manner from jurisdiction to jurisdiction. This is important <br />due to the potential for overlapping impacts among jurisdictions. It is also important to maintain <br />flexibility within a quantitative process to allow transportation professionals at local jurisdictions <br />to add areas to the study which are of specific concern, It is not intended that CMP practices <br />should restrict this aspect of each agency's existing TIA process. <br />It is recommended that the study area for CMP Highway System links be defined by a measure <br />of significant impact on the roadway links. As a starting point, it is proposed that the measure be <br />three percent of existing roadway capacity. Thus, when a traffic impact analysis is being done it <br />would require the inclusion of CMP roadway links that are impacted by 3 percent or more of <br />their LOS E capacity. If a TIA is required only for CMP purposes, the study area would end <br />when traffic falls below three percent of capacity on individual roadway links. If the TIA is also <br />required for other purposes, additional analysis can be required by the local jurisdiction based on <br />engineering judgment or local regulation as applicable. <br />Background Traffic <br />In order for a reasonable assessment of the level of service on the CMP network, it is necessary <br />to not only identify the proposed development impact, but also the other traffic which can be <br />expected to occur during the development of the project. There are numerous methods of <br />evaluating background traffic. The implications of these alternative methods are that certain <br />methodologies may result in deficiencies, while other methodologies may find an acceptable <br />operating conditions. <br />Final -80- OCTA <br />12/18/2009 <br />