RoundaboutDesigner

An ArcGIS Pro add-in that screens every intersection in a U.S. city for roundabout conversion potential, ranks the candidates, recommends a roundabout type, estimates planning-level cost, and lets you refine the results by chatting with a Gemini-powered assistant.

Built as the final project for GEOG 58 at Dartmouth College.

Why

Roundabouts reduce serious crashes, cut idle time, and cost less to maintain than signals, yet they are underused in the U.S. A big reason is that finding good sites is slow: a planner has to pull traffic counts, crash records, right-of-way, and land use for each intersection and apply engineering judgment one site at a time. RoundaboutDesigner automates that first-pass screening so engineering staff can spend their time on the sites most likely to pay off.

What it does

1. Pick a study area. Search any U.S. city or town; boundaries come from Census TIGERweb.
2. Pull open data automatically. Road network and intersections (OpenStreetMap / Overpass), traffic volumes (FHWA HPMS), fatal crashes (NHTSA FARS), structures and value (USACE National Structure Inventory), and commute mode share (Census ACS). The pane shows live status for each source.
3. Score every intersection on five weighted criteria (Safety, Traffic, Feasibility, Multimodal, Destinations), normalized within the study area to a 0 to 100 score. Weights are adjustable with sliders.
4. Recommend a type (mini, single-lane, or multi-lane) from entering volume, posted speed, and leg balance, following FHWA planning guidance.
5. Estimate cost from footprint, lane count, utility relocation per leg, right-of-way acquisition, and a 30% contingency.
6. Write a candidate feature class to the project geodatabase, symbolized by score, with attributes for type, cost, safety benefit, and score breakdown.
7. Chat to refine. The assistant uses Gemini function calling to filter, sort, re-weight, zoom to, and explain candidates, and grounds its answers in the FHWA Roundabouts: An Informational Guide and CMF Clearinghouse data through retrieval-augmented generation (RAG).

Candidates on the map	Top candidates and score breakdown	Assistant

Assistant tools

GetCurrentState, RunFullAnalysis, FilterResults, SortCandidates, AdjustWeights, GetCandidateDetails, SummarizeResults, ZoomToCandidate, ExplainScore, ExplainRecommendation, EstimateBenefit

Example prompts:

• "Only show candidates under $2M"
• "Prioritize sites near schools"
• "Why is #1 ranked first?"
• "Zoom to candidate 3 and explain the recommended type"

Architecture

RoundaboutDesigner/
├── Config/            AppConfig + ApiKeys.example.json (copy to ApiKeys.json)
├── Gemini/            Gemini REST client (chat, function calling, embeddings)
├── Knowledgebase/     Prebuilt RAG embeddings (FHWA guide, CMF), U.S. city catalog
│   └── Sources/       Plain-text sources the knowledge bases were built from
├── Models/            Candidate, recommendation, cost, scoring-weight types
├── Services/          Data acquisition, scoring, type rec, cost, RAG, agent tools, layer writer
├── UI/                WPF dock pane (view + view model)
└── Config.daml        Add-in ribbon tab, button, and dock pane

Requirements

• Windows 10/11
• ArcGIS Pro 3.6 (built against 3.6.2) with a license
• Visual Studio 2022 with the ArcGIS Pro SDK for .NET extension and the .NET 8 SDK
• A Gemini API key
• A Census API key
• NHTSA FARS accident CSVs (see below)

ArcGIS Pro releases newer than 3.6 may run on a newer .NET. If the build fails with a framework mismatch, either install Pro 3.6.x or retarget the project to the matching netX.0-windows framework.

Setup

1. Clone

   git clone https://github.com/23garyd/RoundaboutDesigner.git
   

2. Download FARS data. From the NHTSA FARS data page, download the national CSV zip for each year you want (the project used 2020 to 2024). Extract each year's accident.csv, rename it accident_YYYY.csv, and put them in a FARS/ folder. These files are about 25 MB each and are not in the repo.
3. Add your keys. Copy RoundaboutDesigner/Config/ApiKeys.example.json to RoundaboutDesigner/Config/ApiKeys.json and fill in GeminiApiKey, CensusApiKey, and FarsDataFolder (the full path to your FARS/ folder). ApiKeys.json is gitignored.
4. Build. Open RoundaboutDesigner.sln in Visual Studio and build. The build packages and registers the .esriAddinX.
5. Run. Start ArcGIS Pro (F5 in Visual Studio launches it), open any project, go to the Roundabout tab, and click Roundabout Designer.

Usage

1. Search for a city in Study Area and select it.
2. Optionally adjust the Scoring weights and Max candidates.
3. Click Find roundabout candidates. Watch Data Sources as each feed loads.
4. Review Top Candidates and the Score Breakdown; the candidate layer is added to the active map.
5. Ask the Assistant to filter, re-rank, or explain results.

Limitations

• This is a planning-level screening tool, not an engineering design or cost estimate.
• Scores are normalized within each study area, so they compare sites within one run but not across cities.
• FARS covers fatal crashes only; injury and property-damage crashes are not included.
• HPMS volume coverage is sparse on local roads, which can understate traffic for minor intersections.
• Unit costs are fixed national planning constants in CostEstimationService.cs.

Data sources and acknowledgments

• U.S. Census Bureau: TIGERweb, American Community Survey
• OpenStreetMap contributors (ODbL) via the Overpass API
• FHWA Highway Performance Monitoring System (HPMS)
• NHTSA Fatality Analysis Reporting System (FARS)
• USACE National Structure Inventory (NSI)
• FHWA, Roundabouts: An Informational Guide
• CMF Clearinghouse
• Google Gemini API

Author

Gary Ding, Dartmouth College, GEOG 58