Traffic Impact Analysis Scenarios
The Transportation Impact Study (TIS) for the El Dorado County Community Development Agency (CDA) evaluates multiple traffic impact analysis scenarios to determine the potential effects of development projects on the transportation network. The required scenarios depend on the project's size, location, and potential to influence nearby developments. While smaller, isolated projects that align with the General Plan may only require an Existing Conditions analysis, larger projects or those located near other developments may need additional analyses, including Near-Term and Future Conditions assessments.
1. Existing Conditions
The Existing Conditions scenario represents the transportation environment as it currently exists in the study area. It relies on recent field observations and peak-period turning movement counts conducted for at least three hours per study location. Traffic counts must be collected on a Tuesday, Wednesday, or Thursday under clear weather conditions when school is in session. If approved by CDA’s Long-Range Planning (LRP) staff, previously collected traffic count data may be used if it is less than two years old and has been adjusted by an annual growth rate of 1.03%.
The Existing Plus Project Conditions scenario evaluates how the proposed project would alter the existing transportation system across all modes of travel. The study must forecast traffic volumes that reflect current conditions plus the project's traffic generation. Reuse or conversion projects must account for any existing use of the site that will either continue or cease. Project-related trip generation is determined using the latest edition of the ITE Trip Generation Manual. If alternative data sources are used, justification must be provided to CDA’s LRP staff. The study must also document trip distribution assumptions, showing how project-related traffic will be assigned to the road network.
2. Near-Term Conditions (With and Without Project)
The Near-Term Conditions scenario analyzes traffic conditions ten years into the future, both with and without the proposed project. This projection is developed using a straight-line interpolation from current traffic levels to 2035 projections based on the County’s Travel Demand Model (TDM). The roadway network in this analysis includes all projects listed in the County’s Ten-Year Capital Improvement Program (CIP).
3. Future Conditions
The Future Conditions analysis consists of two components:
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Cumulative No Project Conditions: This scenario evaluates anticipated traffic conditions assuming all approved and pending development projects are completed, excluding the proposed project. In most cases, the project site is assumed to be vacant, although some scenarios may require consideration of existing land uses that could continue under ministerial approvals. The transportation network includes all projects in the County’s 20-Year CIP.
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Cumulative Plus Project Conditions: This scenario builds upon the Cumulative No Project Conditions by incorporating the proposed project’s impacts. The El Dorado County Travel Demand Model (TDM) is used to determine project-related trip distribution. This analysis must also consider whether the project would modify existing or planned land uses.
Additional Analysis Requirements
In some cases, additional analysis scenarios may be necessary depending on project-specific factors. These could include assessments of phased development or interim conditions before full project build-out, as determined by CDA’s LRP staff.
For projects that align with General Plan land use and zoning assumptions, a separate 2035 cumulative traffic analysis may not be required. Instead, the study may tier from the General Plan Environmental Impact Report (EIR) and its Cumulative Traffic Analysis. However, a consistency review must be conducted and documented in the TIS, with CDA’s LRP staff confirming whether additional cumulative impact analysis is necessary. If a separate cumulative impact study is required, the land use and transportation assumptions must be developed in coordination with CDA’s LRP staff.
By conducting comprehensive traffic impact analyses across these scenarios, the County ensures informed decision-making and proper mitigation planning to accommodate future transportation demands.
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