What is in the MileCheck API data, and how accurate is it?

Alert records

GET /v1/alerts returns conditions (road weather and surface) and incidents (closures, crashes, construction, hazards). Both are the state's own data in one shape. Fields a state does not publish are null or absent, never guessed.

// incidents[]  (from a live Washington record)
{
  "incident-id": "WA-722671",
  "event-type-id": "RW",            // AC crash, CL closure, RW roadwork, WE weather, HZ hazard, OT other
  "headline": "",
  "impact-desc": "Weekend-long full closure of northbound I-5 ...",
  "priority": "High",              // the DOT's own priority where it gives one
  "event-status": "Open",
  "start-time": "2026-10-29T18:58:00.000Z",   // ISO 8601, UTC
  "end-time":   "2026-10-31T06:59:00.000Z",
  "last-updated": "2026-10-30T16:03:43.363Z",
  "location": {
    "route-id": "SR 5",            // route in the same form as our mile marker data
    "direction": "NB",             // NB SB EB WB, or absent when the DOT gives none or both
    "start-location": { "start-lat": 47.5867, "start-long": -122.3201, "start-mile-marker": 164 },
    "end-location":   { "end-lat": 47.6558,  "end-long": -122.3223,  "end-mile-marker": 169 }
  }
}

Field names in conditions[]: location-name, route-id, latitude, longitude, road-surface-condition, road-surface-condition-id, air-temperature, weather-condition, travel-advisory, restriction-one, restriction-two, date-updated. States fill the ones they publish.

Every response also has source_status per feed: live, or a reason it is not (for example withdrawn when a source was switched off). An empty list with live means the agency reports nothing active. An empty list with anything else does not mean the road is clear.

Which IDs can I store?

Changes between releases

Live endpoints change every minute and have no releases. The licensed mile marker file does: new roads, renumbered routes and corrected positions. Today there is no fixed monthly schedule and no automatic diff file. A delivery is announced when it ships, and on request we send the list of added, removed and moved markers against your last file. An automatic change list with every delivery is on our list to build.

Coverage and source per state

• Mile markers: all 50 states, plus 10 Canadian provinces and territories (kilometres in Canada).
• Live alerts: 49 states plus British Columbia, Alberta and Manitoba.
• Source for each state: the state DOT's own feed. The data sources page lists the agency, the feed and the format for every state.
• Feeds come in 19 formats. We convert each to the one shape above and keep a record of what each state does not give us.

How fresh is it?

We cache most state feeds for 5 minutes. A few are cached longer because the state publishes slowly. generated_at on a response is when we built it, not when the DOT last updated; use last-updated on a record for the DOT's own time. Border waits follow CBP and CBSA; last_updated on each direction is their time.

Accuracy notes

• Mile marker positions are approximate. They are the state's own reference posts, not surveyed sign positions. /v1/locate returns the nearest post within 1 mile and says milepost: null beyond that. Between posts the app interpolates to one decimal; the API returns the post.
• Some states restart numbering. In California and Georgia, route posts restart at each county line, so a route and number can appear in many places. We keep the county with each post in the data files. Do not treat a bare route and number as a unique place in those states.
• Alerts are the DOT's report. We do not confirm them. A crash can be cleared before the DOT updates; a closure can be posted late.
• We change some fields. Route names are rewritten into one form, directions into NB/SB/EB/WB, times into UTC, and event types into the codes above. The original text stays in impact-desc.
• We drop what we cannot place. Alerts on roads not in our route list, such as Texas farm-to-market roads or local streets, are left out rather than shown with a wrong route. In Texas that is about a quarter of the DOT's events.
• Not for emergencies. MileCheck is not an emergency service and does not decide whether a road is safe.

Found something wrong?

Send the request id (X-Request-Id) and what you expected to info@milecheckapp.com. Wrong mile marker data gets fixed in the file and noted in the changelog.