MBTA Tracker

Real-time vehicle tracking for the MBTA network. Select a route in the sidebar and watch buses, trains, and commuter rail cars move on the map. Click a vehicle to see its current stop, next arrival prediction, and how far off schedule it is.

Live: https://mbta.critmind.com/

What it does

• Live vehicle positions on a dark 3D MapLibre GL map, refreshed every 10 seconds
• Route shapes driven by MBTA route patterns (typicality=1) for authoritative shape selection
• Stop markers with MBTA T-logo icons drawn when you select a route
• Per-vehicle arrival predictions and delay status pulled from the MBTA predictions API
• Train departure board: pick a boarding station and direction to see the next arrivals and a per-stop prediction grid for every approaching train, with HERE markers and delay chips (refreshed every 15 seconds; the default view on mobile, with a one-tap toggle to the map)
• System-wide and per-route alert banners with a scrolling ticker for active disruptions
• Persists your last selected route, boarding station, and map position in a cookie

Running locally

You need JDK 17+, Node.js 20+, and npm.

# Terminal 1 — backend on https://localhost:8443
./gradlew run

# Terminal 2 — frontend dev server on http://localhost:4200
# Updates to frontend files are automatically recompiled and the UI updated.
cd frontend
ng serve --proxy-config proxy.conf.json --host=0.0.0.0

The backend generates a self-signed TLS certificate at startup using Bouncy Castle — no keystore file or external keytool step needed. The dev proxy (frontend/proxy.conf.json) forwards /api/** to https://localhost:8443 with certificate validation disabled (secure: false), so no CORS config is needed locally.

Grab a free API key from https://api-v3.mbta.com if you want the higher rate limit (1000 req/min vs 10). Set it before starting the backend:

export MBTA_API_KEY=your_key_here

Stack

The backend is a Scala 3 / Apache Pekko HTTP service that proxies the MBTA v3 REST API, enriches vehicle data with stop names and arrival predictions, and serves the compiled Angular app as static files. There's no separate frontend server in production — Pekko serves everything over HTTPS with a runtime-generated certificate.

Layer	Tech
Backend	Scala 3.3 LTS, Pekko HTTP 1.3, Spray JSON, Bouncy Castle 1.80
Frontend	Angular 20, MapLibre GL JS 5, OpenFreeMap vector tiles, Angular Material, RxJS
Build	Gradle 9, Angular CLI
Infra	AWS ECS Fargate, ECR, API Gateway, ACM, Route 53

Project layout

source/scala/       Scala backend
  MBTAService       HTTP routes + static file serving
  MBTAAccess        Throttled HTTPS client to api-v3.mbta.com
  RequestFlow       Vehicle enrichment pipeline (stops, predictions, alerts, shapes)
  TLSConfig         Runtime self-signed cert generation via Bouncy Castle
  MBTAModels        Domain types

frontend/src/app/
  services/         VehicleService (state), ApiService (HTTP), MapService (MapLibre GL)
  components/       Map, Routes sidebar, Train board, Vehicle list, Alert banner/ticker

Backend API

GET /health
GET /api/routes?type=<0-4>
GET /api/route/:id/vehicles?sortBy=vehicleId&sortOrder=asc
GET /api/route/:id/shapes
GET /api/route/:id/stops
GET /api/route/:id/board
GET /api/route/:id/alerts
GET /api/alerts

Shapes are filtered server-side using the MBTA /route_patterns endpoint — only typicality=1 (typical service) shapes are returned. If the route patterns call fails, all shapes are returned as a fallback.

Linting

The build enforces Scalafix rules (OrganizeImports, RemoveUnused, DisableSyntax). The build task will fail if there are violations.

./gradlew checkScalafixMain   # check
./gradlew scalafixMain        # fix

Deployment

See documents/deployment-guide.md for the full AWS deployment walkthrough. The short version for updating a running deployment:

./gradlew --no-daemon buildAndPush tofuApply