Transportation Impact Analysis Guidelines are designed to ensure that land use intensities outlined in a General Plan align with the capacity of the local circulation system, as mandated by State and Federal laws. A Transportation Study (TS) is required by the City to assess the potential impacts of land use proposals on both the current and future transportation system, ensuring compliance with the California Environmental Quality Act (CEQA) and other applicable laws and guidelines. The TS Guidelines provided by the City of Diamond Bar include both CEQA-based and non-CEQA-based requirements for individuals or entities seeking development approval within the city. These guidelines must be used alongside the City's Local CEQA Guidelines and Municipal Code to navigate the development review process effectively.
Historically, the TS has been a core part of the CEQA process, primarily focusing on analyzing a project's impact on intersections or roadway segments using Level of Service (LOS) metrics. However, with the implementation of Senate Bill 743 (SB 743), the TS process has evolved. Now, a TS may be required as a stand-alone document, serving as a necessary part of the project approval process. This TS will provide information for decision-makers that may not be required as part of CEQA but is essential for evaluating the project’s transportation impacts.
The primary goal of these guidelines is to offer general instructions for analyzing the potential transportation impacts of proposed development projects. The guidelines outline the recommended structure and methodology for preparing a TS, which is essential for assessing changes in both LOS and Vehicle Miles Traveled (VMT) metrics.
When an applicant seeks project approval, they will submit their proposed development along with a planning and land use application to the City. After City Staff conducts a preliminary review, the applicant will be informed by the project planner as to whether or not a TS is required. The TS should account for both LOS and VMT changes that the proposed development may cause. A TS that includes LOS analysis is mandatory for any project that generates more than 50 vehicle trips during either the AM or PM peak hours. Smaller projects may still require a traffic study depending on land use and location, as determined by the City.
Additionally, a TS that includes a VMT assessment is required for any project that does not meet the specified project screening criteria. These criteria include screening for Transit Priority Areas, Low VMT-generating Areas, and specific Project Types. Projects that meet the screening criteria may be exempt from VMT analysis but still require LOS analysis, or vice versa. In instances where insufficient information is available to make a preliminary determination on the project's traffic impacts, the City Traffic Engineer will have the discretion to decide whether a TS is necessary.
The remainder of the guidelines is structured to provide detailed instructions on how to assess General Plan consistency, conduct both LOS and VMT analysis for CEQA compliance, and outline the required format for transportation studies. The document also provides guidelines for evaluating active transportation options and public transit impacts as part of the transportation analysis.
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