openapi: 3.1.0
info:
  title: CTA Bus Tracker Arrivals Follow API
  description: The Chicago Transit Authority Bus Tracker API provides real-time bus arrival predictions, vehicle locations, route patterns, route lists, and stop directories for the CTA bus network. Access requires an API key issued by the CTA Developer Center.
  version: 2.0.0
  contact:
    name: CTA Developer Center
    url: https://www.transitchicago.com/developers/
  license:
    name: CTA Developer License Agreement
    url: https://www.transitchicago.com/developers/terms/
servers:
- url: http://www.ctabustracker.com/bustime/api/v2
  description: CTA Bus Tracker v2 production
security:
- apiKey: []
tags:
- name: Follow
  description: Follow an individual train run
paths:
  /ttfollow.aspx:
    get:
      operationId: followTrain
      summary: Follow This Train
      description: Returns predictions for an individual train run.
      tags:
      - Follow
      parameters:
      - name: key
        in: query
        required: true
        schema:
          type: string
      - name: runnumber
        in: query
        required: true
        description: Train run number to follow.
        schema:
          type: string
      - name: outputType
        in: query
        schema:
          type: string
      responses:
        '200':
          description: Per-run prediction list
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ArrivalsResponse'
components:
  schemas:
    Arrival:
      type: object
      properties:
        staId:
          type: string
        stpId:
          type: string
        staNm:
          type: string
        stpDe:
          type: string
        rn:
          type: string
        rt:
          type: string
        destSt:
          type: string
        destNm:
          type: string
        prdt:
          type: string
        arrT:
          type: string
        isApp:
          type: string
        isSch:
          type: string
        isDly:
          type: string
        lat:
          type: string
        lon:
          type: string
        heading:
          type: string
    ArrivalsResponse:
      type: object
      properties:
        ctatt:
          type: object
          properties:
            tmst:
              type: string
            errCd:
              type: string
            errNm:
              type: string
            eta:
              type: array
              items:
                $ref: '#/components/schemas/Arrival'
  securitySchemes:
    apiKey:
      type: apiKey
      in: query
      name: key