A Transportation Impact Analysis (TIA) (aka “Traffic Study") may be required whenever a development proposal is expected to generate a significant number of vehicle trips or where there are already traffic congestion problems on the City transportation system. Generally, 50 or more pm peak-hour (aka: evening rush hour) vehicle trips are considered significant enough to warrant a TIA, however, this can vary considerably depending on the specific land use-transportation context where development is proposed in the City. In places where there are known traffic congestion issues at signalized intersections or public safety issues (collision history), City transportation planners may use professional judgement to require that a TIA be performed, even when the proposed development is expected to produce less than 50 pm peak hour vehicle trips.
TIAs must be conducted by a licensed engineer in Washington and must comply with all procedures and requirements listed under
Section 11 of the
Public Works Development Guidelines and Improvement Standards.
The engineer hired by the private developer to perform the TIA is required to work with City transportation planners to address to scope of the TIA, including intersections of concern, the distribution of the project traffic on the City transportation network, and a review of mitigating measures that may be needed to address the transportation impacts identified.
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