City of Austin Transportation Impact Analysis Guidelines – Summary & Rewritten Guidance
Projected Volume Analysis
Projected volume analysis ensures street cross-sections are suitable for anticipated traffic volumes at full buildout. For internal and Level 1 streets adjacent to a development, street classification (Street Level) should be recommended based on daily traffic volumes, using TCM Section 2 and the Austin Strategic Mobility Plan (ASMP) as references. The analysis must include pedestrian and bicycle infrastructure, buffers, and planting zones. Where daily volumes aren’t available, estimates may be derived by applying a factor (10 for general uses, 8 for industrial) to the average peak-hour volume between adjacent intersections.
Access Management and Queuing Analysis
This analysis ensures safe, efficient access to/from the site. Drive-thru uses and schools may require a queuing study to verify sufficient on-site storage for anticipated queues. The analysis should:
-
Minimize driveway access points to reduce conflict points.
-
Evaluate need for deceleration/acceleration lanes.
-
Address on-site operations including drop-offs, valet, trash, and loading/unloading areas.
-
Demonstrate, if required, that queuing won’t extend into the public ROW.
Full TIA Scoping
A Full TIA requires a broader study area than a Transportation Assessment. It must include:
-
All intersections within ¼ mile of the site, as identified in the ASMP.
-
If adjacent to a Level 5 street, analysis extends to the farthest Level 4 frontage road.
-
Intersections within ½ mile are included if 50+ peak-hour trips pass through them.
-
Identification of all nearby planned/existing schools, transit stops, trails, sidewalks, and bike facilities.
Study Requirements Overview
All Transportation Impact Analyses must include the following components:
1. Executive Summary
Provide an overview of the project, including purpose, location, land use, access, trip generation, and key findings (LOS, V/C ratios, mitigation).
2. Table of Contents
Include all report sections, tables, figures, and appendices.
3. Introduction and Background
Summarize the project location, land use, intensity, trip generation, access, and buildout year. Include:
-
A site and study area map.
-
A site plan showing proposed land use and driveways.
4. Existing Road Network
Describe all roads in the study area, including classification, speed limit, number of lanes, sidewalks, medians, bike lanes, and planned improvements.
5. Relevant Mobility Plans
List all applicable planning documents (e.g., ASMP, corridor plans, TxDOT plans) referenced during scoping.
Capacity Analysis Methodology
Each analysis scenario (Existing, No-Build, Build, and Mitigated) should follow these guidelines:
-
Use Synchro (and SIDRA for roundabouts) for AM/PM peak hour modeling. Additional peaks (midday, weekend) may be required.
-
All scenarios must be modeled in a single, connected Synchro file with real-world coordinates.
-
Signal timing data must be sourced from AMD or TxDOT.
-
HCM results must be presented in a summary table (preferably 11”x17”). Synchro lane/volume/timing reports should be included if HCM is not applicable.
Performance Thresholds:
-
Outside Urban Core: Poor performance = LOS E/F or V/C > 0.95. Mitigation should aim to maintain LOS D or better and V/C < 0.95.
-
Inside Urban Core: LOS E/F may be acceptable with justification. Focus should shift to non-vehicular mitigation (TDM, pedestrian, bike, transit improvements).
Where Synchro analysis indicates poor performance, validation should occur through field observation (Existing) or SimTraffic simulation (Build).
Projected Volume Analysis (Expanded)
In addition to intersection capacity, projected volume analysis helps define appropriate street cross-sections. Present findings in a table format, including daily volumes and corresponding recommended Street Levels. Where daily volumes are unavailable:
-
Use peak-hour segment volumes between intersections.
-
Multiply by 10 (or 8 for industrial areas) to estimate daily traffic.
Scenario-Based Conditions
1. Existing Conditions
Include:
-
Date and quality of traffic counts.
-
AM/PM peak volume exhibits.
-
Description of existing intersections (control type, lanes, ongoing improvements).
-
Summary of Synchro results.
2. No-Build Conditions
Outline future conditions without the development:
-
Apply annual growth and include approved background projects with trip generation/distribution.
-
Show future lane configurations and signals.
-
Include AM/PM volume exhibits.
-
Highlight movements worsening from LOS D to E/F.
3. Build Conditions
Describe the development, including:
-
Trip generation (daily, AM/PM), reductions (pass-by, internal capture, TDM).
-
Summary and appendix of the TDM Plan.
-
Site plan with proposed access.
-
Trip distribution and traffic volume exhibits.
-
Discussion of intersection performance degradation from No-Build to Build.
-
Projected volume analysis tables and recommended cross-sections.
4. Mitigated Conditions
Detail proposed improvements to offset impacts:
-
Identify mitigation for each phase.
-
Include conceptual exhibits showing ROW, lane widths, sidewalks, signals, bike/transit features, and driveway spacing.
-
Avoid mitigation that worsens safety or other traffic movements.
-
Include analysis results and note movements still performing poorly post-mitigation.