Transportation Impact Analysis (TIA) Format and Required Elements – City of Issaquah
A Transportation Impact Analysis (TIA) prepared for a development project in the City of Issaquah must follow a consistent and comprehensive format to ensure clarity, accuracy, and ease of review. The TIA should clearly document the purpose, methodology, data sources, assumptions, findings, conclusions, and recommendations of the study. Since this report may be reviewed by both technical and non-technical audiences, including decision-makers and the general public, it must be written in a clear, concise, and understandable manner. Technical terminology should be defined, and jargon should be minimized to enhance accessibility.
The TIA must also include a description of any coordination conducted with other jurisdictions or agencies affected by the proposed development. This is essential for ensuring alignment across multiple governmental bodies, especially in cases where transportation systems and services span jurisdictional boundaries.
While the following report structure provides a uniform template for preparing a TIA, it is important to note that not all elements will be necessary for every project. The City of Issaquah will identify the required sections at the TIA scoping meeting, based on the development’s size, type, location, and its potential to generate adverse transportation impacts, as outlined in the City’s thresholds for significant impacts.
1. Report Cover The report cover should display the following information:
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Name and location of the development project
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Applicant’s name
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Name and organization of the preparer
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Date of the report
2. Title Page The title page must include:
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Project name and address
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Development application number
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Applicant’s contact information (name, address, phone number)
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Report date and any applicable revision dates
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Preparer’s contact information (name, title, organization, phone, and address)
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Licensed traffic engineer’s contact information, professional stamp, and license expiration date
3. Table of Contents, List of Figures, Tables, and Appendices To improve navigation and review, the report should include a table of contents, followed by a list of all figures, tables, and appendices.
4. Executive Summary The Executive Summary should offer a high-level overview of the TIA, including:
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The purpose and scope of the study
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A brief project description
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Site location and study area
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Major findings, conclusions, and recommended mitigation measures
5. Description of Proposed Development This section should provide a comprehensive account of the proposed development, including the following elements:
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Vicinity Map: A map illustrating the site location, surrounding transportation network, and boundaries of the study area, as agreed upon during the scoping meeting.
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Nearby Developments: Identify and map approved or proposed developments in proximity to the project. These should be factored into the analysis as part of background assumptions.
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Site Improvements and Facilities: Describe the existing and proposed buildings, appurtenances, fueling stations, drive-throughs, and other features.
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Development Size and Use: Include total square footage, number of residential units, types of land use, and a summary of the floor area by land use category.
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Current and Proposed Zoning: Describe existing and proposed zoning. For analysis purposes, the land use generating the highest traffic volumes (worst-case scenario) should be assumed unless a specific use is committed to by the applicant.
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Parking Information: Provide details on the quantity and dimensions of proposed parking spaces, along with circulation patterns.
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Site Plan: Include a detailed site plan showing:
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Access points, their location, and types (e.g., full access, right-in/right-out)
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Driveway throat lengths
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Sight distances
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Adjacent access points or streets
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Internal vehicle, pedestrian, and bicycle circulation patterns
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Traffic control devices
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Design vehicle tracking for access, internal circulation, service, and emergency access
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Distances to existing street and driveway connections
If no site plan is available, a conceptual/prototypical layout must be used with updates submitted once a final site plan becomes available. The site plan should be presented at a scale suitable for City review and may be included as an appendix or attachment.
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Development Schedule and Phasing: Detail anticipated phasing, including completion timelines for each phase and expected full build-out date.
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Traffic Analysis Years: Present analysis for future conditions with and without the proposed development, accounting for all pipeline projects and background traffic growth at key access points and non-concurrency intersections. The City will provide or approve background growth data.
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Peak Analysis Periods: The primary analysis period is typically the weekday PM peak hour. Depending on the development type, other periods such as AM, midday, weekend, or holiday peaks may be required or excluded based on City approval.
6. Existing Conditions The TIA should provide a thorough assessment of the existing transportation system in the study area. This includes:
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Roadway Descriptions: For each roadway impacted by the project:
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Number of lanes, lane usage (e.g., turn lanes, parking lanes)
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Pavement material
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Right-of-way and shoulder widths
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Sidewalk widths and conditions
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Roadway classification (e.g., arterial, collector)
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Posted speed limits
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Topography
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Traffic Control Devices: Identify all signals, stop signs, pavement markings, and signage affecting or affected by the project.
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Access Spacing and Alignment: Report the spacing and alignment between existing streets/driveways and proposed development access points.
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On-Street Parking: Document the availability and usage of on-street parking near the project, especially if it impacts key intersections.
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Truck and Heavy Vehicle Access: Note any vehicle restrictions and truck routes.
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Pedestrian Facilities: Map and describe marked crosswalks, school walking routes, and other relevant pedestrian facilities.
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Bicycle Facilities: Include existing and proposed bike lanes, trails, or multi-use paths adjacent to or connected to the site.
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Transit Facilities: Identify nearby bus routes, frequency of service, stop locations, and available amenities (shelters, benches, lighting).
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Design Vehicle Maneuverability: Use AASHTO guidelines to identify minimum turning paths for design vehicles. Include turning radii for existing and proposed access points.
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Other Relevant Information: Any additional factors that may influence transportation performance and safety around the site should also be included.
This format ensures that Transportation Impact Analyses submitted to the City of Issaquah are clear, thorough, and consistent with city standards and review expectations. Applicants are encouraged to work closely with City staff throughout the process to ensure compliance and streamline the review process.
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