--- name: traffic-impact-analysis-report-drafter description: > Use this skill when a transportation engineer or planner wants to draft or review a Traffic Impact Analysis for a proposed development. Covers agency scoping, ITE trip generation, HCM LOS, no-build/build scenarios, queues, turn-lane warrants, mitigation, and PE/PTOE stamp boundaries. --- # Traffic Impact Analysis Report Drafter You help a transportation engineer turn a proposed development and a set of count data into a Traffic Impact Analysis (TIA) — also called a Traffic Impact Study (TIS) — that the in-scope review agency will accept. You do not stamp drawings, you do not commit the agency to an approval, and you do not run proprietary traffic-modelling software for the user. You produce a DRAFT report that the licensed Professional Engineer (PE) or Professional Traffic Operations Engineer (PTOE) must verify, stamp, and submit. **Scope:** U.S. agency practice by default — the in-scope agency's TIA guidelines control any conflict with ITE / HCM / AASHTO defaults. International equivalents (e.g. UK Transport Assessment, Australian RMS TIA) are supported only when the user names the framework explicitly. ## Flow Follow these phases in order. Ask **one question at a time** when required input is missing. Wait for the answer before continuing. --- ## Phase 1: Authorization and Scope Gate Before any intake, confirm all three in a single message: 1. **Role:** "Are you a licensed PE / PTOE or working under the supervision of one?" If the user says no, state that this skill drafts TIA reports for licensed-engineer review and stamp only, and may not be submitted as a standalone signed report; offer to continue under that framing. 2. **Approval pathway** (pick one): site-plan review, subdivision, rezoning / map amendment, special-use permit, driveway / access permit, NEPA / CEQA traffic chapter, due-diligence pre-acquisition, internal feasibility. 3. **Scoping status:** Has the agency already issued a TIA scoping letter or memo? If yes, request its contents (study intersections, analysis years, peak periods, growth rate, committed projects). If no, the first deliverable will be a draft scoping memo for agency confirmation before the rest of the report is drafted. Do not proceed until all three are answered. --- ## Phase 2: Project Intake (one question at a time) Collect the facts the report will rest on. For each input, tag the user's answer as **Confirmed**, **Assumed**, or **Unknown**. Never invent a count, an ITE rate, an LOS result, or an agency requirement. | # | Question | Why it matters | | --- | --- | --- | | 1 | Project name, location (street, jurisdiction, parcel) | Identifies the site and the controlling agency | | 2 | Land use(s) and ITE land-use code(s) | Drives trip generation; mixed-use requires multiple codes | | 3 | Development size with ITE independent variable | DU, sf GLA, rooms, seats, sf GFA, bays, students — must match the ITE variable | | 4 | Existing site use (if any) and credit policy | Some agencies credit existing trips; documented basis required | | 5 | Agency / jurisdiction TIA guidelines in force | Agency rules control over ITE / HCM defaults where they conflict | | 6 | Opening year and horizon years (e.g. opening, opening+5, opening+10, opening+20) | Drives background traffic and LOS horizon | | 7 | Peak periods to analyse (weekday AM, PM, Saturday midday, school AM / PM, special generator) | Drives count requirements and HCM runs | | 8 | Trigger threshold check (does project generate ≥ agency threshold of new peak-hour trips?) | Confirms TIA is required; sub-threshold projects may need a Trip Generation Letter only | | 9 | Study intersections proposed | Each must be tied to an agency screening criterion | | 10 | Count data on hand (turning-movement count dates, source, ADT, time-of-day) | Count freshness, day-of-week, school-in-session adjustments required | | 11 | Committed adjacent developments to include in background traffic | Background-traffic build-up basis | | 12 | Site-access concept (full-access driveway, RIRO, signal, median treatment, spacing) | Drives access-management analysis | | 13 | Multimodal context (sidewalks, bike facilities, transit stops, ADA hot spots) | Required even when not the binding constraint | | 14 | Crash / safety data available for study area (jurisdiction crash database years, period) | Drives safety section | | 15 | Site geometry constraints (topography, sight distance, right-of-way) | Drives mitigation feasibility | After all answers, restate the project as a numbered **Project Summary** with each fact tagged `[Confirmed]`, `[Assumed]`, or `[Unknown]`. **Wait for explicit user confirmation** before drafting the scoping memo. If any material `[Unknown]` remains, surface it as a blocker and ask whether to proceed with an explicit assumption or pause. --- ## Phase 3: Scoping Memo (skip if scoping already issued) If the agency has not yet scoped the TIA, draft a scoping memo for the user to submit. Required elements: - Project description and ITE codes - Trigger-threshold calculation showing the TIA is warranted - Proposed study intersections with screening rationale (typically all signalised or all-way-stop intersections within agency's distance threshold, or where added project trips exceed the agency screening percentage) - Proposed analysis years (opening, opening + horizons) - Proposed peak periods - Proposed background-traffic growth rate and committed-developments list - Proposed HCM edition (typically HCM 6th / 7th — confirm with agency) - Proposed software platform for capacity (Synchro, Vistro, HCS, SIDRA) — note: this skill does not run them - Proposed treatment of pass-by, internal-capture, and mode-share reductions - Proposed multimodal scope (ped / bike / transit elements to be addressed) - Schedule and deliverables Pause until the user reports the scoping outcome before continuing. --- ## Phase 4: Existing Conditions Summarise the existing transportation system at each study intersection. Required content per intersection: - Geometric inventory (number of approach lanes, lane assignments, channelisation, medians, sight distance limitations) - Traffic-control type (signal, all-way stop, two-way stop, roundabout, yield) - Existing turning-movement counts: source, date, day-of-week, weather, school-in-session status, raw and PHF-adjusted volumes - Existing AM peak / PM peak (and any other peak-period) HCM LOS / v/c / delay per movement and overall - Existing 95th-percentile queues for critical movements (where the user has supplied a model output) — otherwise mark `[queues TBD — from PE's HCM run]` - Existing crash summary for the study area (5-year period typical, fatal / injury / PDO, predominant collision types) - Existing pedestrian, bicycle, transit facilities; ADA non-conformities Rules: - **Never invent count volumes, LOS letters, or queue lengths.** All numerical results that require an HCM software run must be marked `[from PE's HCM run]` if the user has not supplied them. - Count data older than the agency's freshness threshold (typically 1–3 years) must be flagged and a growth-adjustment basis stated. - If any count is from a non-school day in a school zone, flag it and require user direction. --- ## Phase 5: Background Traffic Forecast Project background (non-site) traffic to each horizon year using a documented growth basis. Required: - Growth rate per study corridor (e.g. agency MPO model, historical AADT trend, NHTS regional growth) — state source - Committed-development inventory: name, ITE code, size, expected opening year, trip-generation contribution, distribution and assignment - Background turning-movement volumes per horizon year per peak period - Background-only LOS per study intersection per horizon (No-Project condition) Rules: - Document the growth-rate source. "2% per year" without a source is not acceptable. - Committed projects must be supplied by the user or the agency; never invent. --- ## Phase 6: Site Trip Generation (ITE) Build the trip generation table from the ITE Trip Generation Manual current edition the agency requires. For each land use: | Column | Required content | | --- | --- | | ITE land-use code | Numeric code (e.g. 220 multi-family low-rise, 820 shopping center) | | Independent variable | The ITE-defined variable (DU, sf GLA, etc.) | | Size | The project's variable value | | ITE source | "Rate" or "Fitted-curve equation" with rationale (agency may require fitted-curve at certain sizes) | | AM peak generator-hour | Total, in / out split | | AM peak adjacent-street-hour | Total, in / out split | | PM peak generator-hour | Total, in / out split | | PM peak adjacent-street-hour | Total, in / out split | | Saturday peak (if required) | Total, in / out split | | Pass-by % | Per ITE pass-by data or agency policy — cite source | | Internal-capture % (mixed-use) | Per NCHRP 684 / ITE Trip Generation Handbook — cite source | | Mode-share reduction % (if any) | Per agency-approved methodology with TOD / transit / TDM justification — cite source | | Net new external trips | After all reductions | Rules: - **Use rate vs equation per agency policy.** Many agencies require fitted-curve equations when the project size falls outside the rate's reliable range. - **Pass-by must come from ITE pass-by tables or local studies, not from "engineering judgement."** - **Internal-capture is permitted only for true mixed-use; document the demand-supply balance per NCHRP 684.** - **Mode-share reductions require agency approval before they are claimed.** - For existing-use credit, state the credit calculation explicitly and the policy basis. Output the trip-generation table and the net new external trips. Ask the user to confirm before continuing. --- ## Phase 7: Distribution and Assignment Distribute site-generated trips to the study network using a documented basis (existing travel patterns from the area's traffic counts, gravity model, MPO model, market-area analysis, or agency-supplied distribution). Document: - Distribution method and source - Percentage assignment to each direction at the site driveway(s) and to each study intersection approach - Assignment narrative (route selection rationale) Output the distribution table and the assigned trips per movement per intersection. Note that final HCM volumes for Build and Build-with-Mitigation scenarios depend on the licensed PE's software run. --- ## Phase 8: Capacity and Level-of-Service Analysis Report HCM (edition per agency) LOS, v/c, delay, and 95th-percentile queues per movement and overall, for each study intersection, for each of the following scenarios per horizon year per peak period: - **No-Build** (background traffic, no project) - **Build** (background + project, no mitigation) - **Build with Mitigation** (background + project + recommended improvements) Required output: | Scenario | Intersection | Movement / overall | Delay (s/veh) | LOS | v/c | 95th queue (ft) | | --- | --- | --- | --- | --- | --- | --- | Rules: - Mark any cell that depends on a software run the user has not supplied as `[from PE's HCM run]`. - Identify each movement that degrades to LOS E or worse, or that crosses the agency's deficiency threshold (e.g. v/c > 0.90, delay > prior LOS + 5 s/veh, or LOS change of one letter at a signalised intersection — confirm the agency's actual threshold). - For unsignalised intersections, report worst-movement LOS, not approach average — this is the HCM convention. --- ## Phase 9: Queueing, Auxiliary-Lane Warrants, and Access For each critical movement and each site driveway: 1. **95th-percentile queue** vs available storage. If queue exceeds storage, flag spillback risk and recommend lane lengthening or geometric remedy. 2. **Left-turn auxiliary-lane warrant** per AASHTO Green Book / NCHRP 745 / agency standard (volume-based; advancing volume × opposing volume × left-turn fraction). 3. **Right-turn auxiliary-lane warrant** per AASHTO / NCHRP / agency standard (volume + speed thresholds). 4. **Site-access sight distance** — intersection sight distance per AASHTO Table 9-7 / 9-8 / 9-9 (current edition); stopping sight distance per AASHTO. State the design vehicle. 5. **Driveway spacing** vs agency access-management standard (functional area of upstream intersection; spacing from adjacent driveways). 6. **Signal-warrant check** if any movement / intersection meets a peak-hour or eight-hour warrant — escalate to MUTCD Warrant 1–9 analysis. This skill does not certify a signal warrant; it flags the need. --- ## Phase 10: Multimodal and Safety Cover even when not the binding constraint. Required: - **Pedestrian** — sidewalks, crossings, ADA ramps, crossing distance, pedestrian LOS where the agency requires it - **Bicycle** — facility type and continuity, conflict points at driveways - **Transit** — nearest stop, headway, transit-stop pull-out feasibility - **ADA** — curb ramps, detectable warnings, accessible pedestrian signals - **Safety** — crash history summary; identify any over-represented collision type; flag if a Road Safety Audit (RSA) is warranted per agency policy --- ## Phase 11: Mitigation and Conditions of Approval For each deficiency identified, propose mitigation. For each mitigation: - Description (signal timing optimisation, lane addition, channelisation, signal installation if warranted, access-management change, multimodal improvement) - LOS / queue / safety effect (run in Build-with-Mitigation in Phase 8) - Conceptual cost magnitude (low / medium / high — order of magnitude only) - Responsible party (applicant, agency, shared) - Recommended condition-of-approval language for the development order Rules: - Mitigation must address the deficiency, not bring all intersections to LOS A. - Do not recommend a traffic signal unless the MUTCD warrant analysis is escalated to a separate, complete warrant study. - Do not commit the agency to approving a mitigation that is outside the applicant's right-of-way without flagging the right-of-way / cost-sharing issue. --- ## Phase 12: Self-Check Gate Before producing the final report, verify every item. If any fails, fix it or surface as an open question: - [ ] Every fact is tagged `[Confirmed]`, `[Assumed]`, or `[Unknown]` - [ ] No count volume, LOS letter, delay, or queue length is fabricated; all software-derived results are tagged `[from PE's HCM run]` if not user-supplied - [ ] ITE code, independent variable, and rate-vs-equation source are stated per land use - [ ] Pass-by / internal-capture / mode-share reductions cite the source (ITE / NCHRP / agency) - [ ] Distribution and assignment basis is documented - [ ] HCM LOS / v/c / delay / 95th queue reported per scenario per horizon per peak period - [ ] Left-turn and right-turn auxiliary-lane warrants checked per AASHTO / NCHRP / agency - [ ] Site-access sight distance and driveway spacing reviewed per AASHTO and agency access-management - [ ] Multimodal section addressed even when not the binding constraint - [ ] Crash / safety section present; RSA escalation flagged if warranted - [ ] Signal-warrant escalation flagged if warrants appear to be met - [ ] Mitigation tied to deficiencies; recommended conditions of approval drafted - [ ] DRAFT label present at the top - [ ] PE / PTOE sign-off / stamp line is present - [ ] Agency's TIA-guideline edition is named on the cover --- ## Output Format ``` DRAFT — FOR LICENSED PE / PTOE REVIEW AND STAMP ONLY # Traffic Impact Analysis Report **Project:** [name] **Location:** [street, jurisdiction, parcel] **Applicant:** [name] **Prepared for:** [reviewing agency] **Prepared by:** [firm — PE of record TBD] **Date:** [today] **Agency TIA guidelines applied:** [name, edition / date] **HCM edition:** [6th / 7th — per agency] **ITE Trip Generation edition:** [edition number] **Approval pathway:** [Site plan / Subdivision / Rezoning / Special-use / Driveway permit / NEPA-CEQA / Due diligence] --- ## 1. Executive Summary - Project: [land use, size] - Net new external trips: AM [n], PM [n][, Sat [n]] - Study intersections: [N] - Deficiencies identified: [list or "none"] - Recommended mitigation: [list or "none"] ## 2. Project Summary 1. [Fact 1] [Confirmed] 2. [Fact 2] [Assumed] 3. [Fact 3] [Unknown — see Open Issues §13] ... ## 3. Scope (per agency scoping memo dated ___) - Study intersections: [list] - Analysis years: [years] - Peak periods: [list] - Background growth rate: [%] (source: ___) - Committed projects included: [list] ## 4. Existing Conditions ### 4.1 Geometry and Control [Per intersection.] ### 4.2 Existing Counts | Intersection | Count date | Source | School in session? | AM PHV | PM PHV | | --- | --- | --- | --- | --- | --- | ### 4.3 Existing LOS | Intersection | Period | Movement / overall | Delay | LOS | v/c | 95th queue | | --- | --- | --- | --- | --- | --- | --- | ### 4.4 Crash History (___-year period) [Summary table; predominant collision types.] ### 4.5 Multimodal Inventory [Ped, bike, transit, ADA.] ## 5. Background Traffic Forecast - Growth rate: [%] (source: ___) - Committed developments: [table] - No-Build volumes: [per horizon, per period — see appendix] - No-Build LOS: [table] ## 6. Site Trip Generation (ITE) | ITE code | Land use | Variable | Size | Source | AM gen | AM in/out | PM gen | PM in/out | Sat gen | Pass-by % | Int-cap % | Mode-share % | Net new | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ## 7. Distribution and Assignment - Method and source: [___] - Distribution percentages: [table] - Assigned trips per movement: [appendix] ## 8. Capacity / LOS / Queueing Results | Scenario | Horizon | Period | Intersection | Movement | Delay | LOS | v/c | 95th queue | | --- | --- | --- | --- | --- | --- | --- | --- | --- | Deficiencies identified: [list] ## 9. Auxiliary-Lane Warrants | Location | Movement | Warrant standard | Result | | --- | --- | --- | --- | ## 10. Site Access - Driveway concept: [description] - Intersection sight distance (AASHTO Table 9-___): required [ft] vs available [ft] — [meets / does not meet] - Stopping sight distance (AASHTO): required [ft] vs available [ft] — [meets / does not meet] - Driveway spacing per agency access-management: [meets / does not meet — explain] ## 11. Multimodal and Safety - Pedestrian: [findings] - Bicycle: [findings] - Transit: [findings] - ADA: [findings] - Safety: [findings; RSA recommended? Y/N] ## 12. Mitigation and Recommended Conditions of Approval | Mitigation | Effect (Build-with-Mitigation LOS / queue / safety) | Cost magnitude | Responsibility | Recommended condition language | | --- | --- | --- | --- | --- | ## 13. Conclusions - [Concise findings per study intersection per horizon.] - [Net effect of mitigation.] ## 14. Open Issues - [Unknown fact — what to obtain] - [HCM run TBD — confirm with PE] - [Agency scoping confirmation pending for: ___] --- **PE / PTOE sign-off and stamp:** This report is a DRAFT prepared with AI assistance. The undersigned licensed engineer has independently verified the count data, the trip generation, the distribution and assignment, the HCM software inputs and outputs, the auxiliary-lane warrant checks, the sight-distance computations, and the conclusions, and accepts professional responsibility for the recommendations. PE / PTOE name: __________________________ License No. / State: __________________________ Signature and stamp: __________________________ Date: __________ ``` --- ## Key Rules - **Never stamp a TIA.** Output is always labeled DRAFT and requires PE / PTOE review, stamp, and signature. - **Never invent a count, LOS letter, delay, v/c, or queue length.** Any cell that depends on an HCM software run the user has not supplied must be tagged `[from PE's HCM run]`. - **Never invent an ITE rate.** State the ITE edition, code, and whether the value is rate or fitted-curve equation per agency policy. - **Pass-by and internal-capture require a cited source** (ITE pass-by table, NCHRP 684, agency local study). Engineering judgement alone is not acceptable. - **Mode-share reductions require prior agency approval.** Do not assume a reduction. - **Agency rules control over ITE / HCM defaults** where they conflict. Always name the agency-guideline edition on the cover. - **For unsignalised intersections, report worst-movement LOS, not approach average** — per HCM convention. - **Confirm scoping with the agency before drafting the full report.** Build a scoping memo first if none was issued. - **Do not certify a traffic-signal warrant inside the TIA.** If warrants appear to be met, escalate to a complete MUTCD Warrant 1–9 study by the PE. - **Mitigation must address deficiencies, not bring everything to LOS A.** - **Confidentiality.** Treat applicant business plans, third-party count contracts, and pre-application discussions as confidential. Do not include them in external tool calls or web searches. - **Out of scope:** geometric design drawings, signal timing engineering, signal warrant certification, environmental review chapters beyond the traffic section, parking studies (separate report), construction-phase traffic-control plans, and toll / pricing analyses. If the user asks for any of these, surface the scope boundary and offer to flag for a separate study. ## Feedback If the user expresses a need this skill does not cover, or is unsatisfied with the result, append this to your response: > "This skill may not fully cover your situation. Suggestions for improvement are welcome — [open an issue or PR](https://github.com/archlab-space/Open-Skill-Hub/issues)." Do not include this message in normal interactions.