Comprehensive Guidelines for Transportation Impact Analysis Scoping, Trip Generation, and Study Area Requirements in the City of Austin

4.3.3 Transportation Assessment Scoping

A Transportation Assessment is essentially a scaled-down Full TIA study, but applies to developments generating between 2,000 and 4,999 unadjusted daily vehicle trips. All scoping requirements for a Transportation Assessment apply equally to Full TIAs. When an Assessment is required (as determined by an approved TIA Determination Worksheet), applicants must submit a Transportation Assessment scope via the TIA Portal for review by Transportation Development Services (TDS). At a minimum, the scoping submission should include:

1. A project location map

2. A site plan

3. The completed TIA Determination Worksheet

4. Proposed land uses, sizes, and development intensity

5. Any phased buildout plans and projected full-build year

6. The projected annual traffic growth rate based on historical data

7. Estimated daily and AM/PM peak hour trip generation

8. Pass-by trip reduction assumptions

9. Trip distribution exhibits showing volumes and percentages

10. A list of intersections and future intersections included in capacity analysis

11. Roadways for projected volume analysis

12. Agencies whose roadways will be affected (e.g., TxDOT, Travis County)

13. Access Management Analysis if new driveways are proposed, or Queueing Analysis for land uses likely to generate on-site queues (e.g., drive-thrus)

14. Any TDM reduction percentage derived from an approved TDM Plan

4.3.4 Study Area Selection Guidance

When selecting intersections and roadways for analysis, applicants must document their methodology within the scope and follow these criteria:

• All site access points, including driveways, must be included regardless of traffic volume.

• Intersections within ¼ mile of the site boundary that carry 100 or more peak-hour trips (AM or PM) should generally be assessed. The TDS Lead Engineer may adjust this threshold based on geometric constraints or safety concerns (e.g., skewed intersections, limited sight distance).

• Deliverables must include exhibits identifying trip distribution (percentages and volumes for AM and PM), and a separate map showing study intersections and site location.

4.3.5 Trip Generation Approach

Trip generation estimates must adhere to the most recent Institute of Transportation Engineers (ITE) Trip Generation Manual. Use Figure 4.2 from the ITE Handbook, 3rd Edition, to choose between Average Rate and Fitted Curve methodologies based on land use type and intensity. For any uncertainties, applicants should consult the TDS Lead Development Review Engineer.

4.3.6 Vehicle Trip Reductions & Mode Split Guidance

Trip reductions must be applied in a specific order:

1. Pass‑by reductions: follow ITE standards

2. TDM plan reductions: apply the full percentage derived from an approved TDM Plan

3. Existing land use reductions: account for trips from current non-vacant uses

Internal capture reductions are handled within the TDM reduction. After pass-by trips are subtracted, the total TDM percentage is applied. Then existing-trip reductions are factored in to arrive at adjusted trip generation totals.

In rare cases, total reductions may yield zero or negative net trips. In such cases, negative trips may be distributed across study intersections according to trip distribution and used to offset existing traffic counts in the Build scenario. Applicants must consult with the TDS Lead Engineer if such scenarios arise.

4.3.7 Projected Volume Analysis

This analysis ensures recommended street cross-sections align with estimated traffic volumes at full buildout. For internal streets and adjacent Level 1 streets, the applicant should recommend Street Levels based on projected daily volumes. Cross-sections must include pedestrian and bicycle facilities, buffers, and planting zones as outlined in the TCM Section 2 and the Austin Strategic Mobility Plan (ASMP).

Projected volume analysis results should be presented in tabular format. If daily volume data are unavailable, estimates may be calculated using peak-hour traffic counts multiplied by a factor of 10 (or 8 for industrial areas).

4.3.8 Access Management & Queueing Analysis

• Access Management Analysis is required when new driveways are proposed or if sight distance is limited.

• Queueing Analysis is required for uses with expected onsite queueing (such as drive-thrus or school drop-off zones). This analysis must document predicted queue lengths and ensure adequate onsite storage to prevent spillover.

4.3.9 Full TIA Scoping

A Full TIA follows all scoping requirements of a Transportation Assessment, with the main difference being study area criteria:

1. The study must include all existing and planned intersections within ¼ mile, or along the site boundary—depending on the road’s Street Level from ASMP. For adjacent Level 5 streets, analysis extends to the farthest Level 4 frontage road intersection.

2. Additional intersections may be included if within ½ mile of site and carrying 50 or more peak-hour trips, at the discretion of the TDS Lead Engineer.

3. All nearby mobility infrastructure—school sites, transit routes/stops, sidewalks, bike lanes—within ¼ mile must be noted as part of the study area.

4.4 Study Requirements & Structure

Completed TIA submissions must include:

• Executive Summary: Overview of study purpose, site description, access, trip generation, methodology, key findings, and proposed mitigation measures.

• Table of Contents: Including list of tables, figures, and appendices.

• Introduction & Background: Project synopsis, study methodology, and key context.

• Existing Road Network: Description of roadway types, speeds, lanes, and planned improvements.

• Relevant Mobility Plans: Reference key documents such as the ASMP, corridor plans, or TxDOT plans.

• Capacity Analysis Methodology: Description of analysis software (Synchro, SIDRA) and scenarios (Existing, No-Build, Build, Mitigated). Include signal timing plans or reasonable assumptions when necessary.

Presentation of Results:

• Capacity analysis outputs (HCM standards preferred) should be formatted in large tables (11"×17").

• Synchro output should only supplement HCM data when HCM cannot evaluate operations.

• Where intersection performance appears poor, submit field observations or SimTraffic simulations for validation.

Intersection Performance Thresholds

• Outside urban core: Poor performance defined as LOS E/F or Volume/Capacity > 0.95. Mitigation efforts should aim for LOS D or better, or V/C < 0.95. Queuing that impacts adjacent intersections or travel lanes must be mitigated.

• Within urban core: LOS E/F may be acceptable, depending on context. Where roadway capacity improvements are limited, non-vehicular mobility options—identified through TDM—play a critical role in mitigating impacts.

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