specification: API Commons Rate Limits
specificationVersion: '0.1'
schema: https://raw.githubusercontent.com/api-evangelist/interface-research/main/schema/api-commons.yml#/$defs/RateLimits
provider: Department of Transportation
providerId: department-of-transportation
created: '2026-05-04'
# Provenance stamped 2026-08-11: this artifact was written by the API Evangelist
# bulk sweep dated 2026-05-04, not harvested from the provider. See roadmap#35.
method: generated
modified: '2026-05-05'
reconciled: true
tags:
  - Federal Government
  - Transportation
  - Vehicles
  - Aviation
  - Motor Carriers
  - Rate Limiting
description: DOT APIs split into two regimes. NHTSA Vehicle Safety (api.nhtsa.gov) is fronted by api.data.gov,
  which enforces a default 1,000-requests-per-hour limit per developer key (raisable via support). NHTSA
  vPIC, FMCSA QCMobile, FAA Airport Status, and the BTS / FRA / FTA / PHMSA open data portals are unauthenticated
  and bounded by fair-use rather than per-key quotas. api.data.gov surfaces 429 with X-RateLimit-* headers;
  open endpoints use standard server throttling.
sources:
  - https://api.data.gov/docs/
  - https://api.nhtsa.gov/
  - https://vpic.nhtsa.dot.gov/api/
headers:
  limit: X-RateLimit-Limit
  remaining: X-RateLimit-Remaining
  reset: X-RateLimit-Reset
  retryAfter: Retry-After
responseCodes:
  throttled: 429
  quotaExceeded: 429
  serviceUnavailable: 503
  forbidden: 403
limits:
  - tier: api-data-gov
    name: api.data.gov default per-key limit
    scope: api-key
    metric: requests_per_hour
    limit: 1000
    timeFrame: hour
    applies:
      - NHTSA Vehicle Safety API
  - tier: api-data-gov
    name: api.data.gov increased limit (raise via support)
    scope: api-key
    metric: requests_per_hour
    limit: 'higher; request via api.data.gov support'
    applies:
      - NHTSA Vehicle Safety API
  - tier: open
    name: Open / fair-use throttle
    scope: IP
    metric: requests_per_minute
    limit: 'fair-use; not published'
    applies:
      - NHTSA vPIC API
      - FMCSA QCMobile API
      - FAA Airport Status API
      - Bureau of Transportation Statistics Data Portal
      - Federal Railroad Administration Safety Data
      - Federal Transit Administration National Transit Database
      - PHMSA Pipeline Safety Data
policies:
  - name: api.data.gov Key Pattern
    description: NHTSA Vehicle Safety endpoints enforce limits at the api.data.gov gateway. Excess returns
      429 with a JSON error and an OVER_RATE_LIMIT code. Increases must be requested via api.data.gov
      support.
  - name: NHTSA vPIC Bulk Pattern
    description: NHTSA vPIC publishes downloadable vehicle data CSV / database snapshots; bulk consumers
      should download the database refresh rather than iterate the REST API.
  - name: FAA Airport Status Cadence
    description: Airport status data refreshes on a short cadence (minutes); avoid sub-minute polling
      since values change rarely outside weather and operational events.
  - name: Backoff Strategy
    description: On 429 / 503 implement exponential backoff with jitter, honoring Retry-After when present.
  - name: Caching Encouragement
    description: All DOT bureaus encourage caching of responses (vehicle data, airport status, motor-carrier
      records) to reduce load on shared infrastructure.
maintainers:
  - FN: Kin Lane
    email: kin@apievangelist.com