Speed limits from across the world, accessed in milliseconds.

1Authenticate with your bearer token

Every request needs a bearer token, issued to authorised customers under your service agreement. Use this on every call — we monitor usage against it.

Authorization: Bearer <your_token>

2Call the Speed endpoint

Pass a single latitude/longitude pair to get the speed limit at that point. The production base URL is https://api.iw-slu.com.

curl -X GET "https://api.iw-slu.com/Speed?latitude=51.5074&longitude=-0.1278" \
  -H "Authorization: Bearer <your_token>"

3Read the response

Every response comes back in the same envelope, whether it succeeds or fails: a message, an error, and a data payload. You are not charged for requests that return an error.

{
  "message": "Success",
  "error": null,
  "data": {
    "id": 184522,
    "latitude": 51.5074,
    "longitude": -0.1278,
    "roadName": "Whitehall",
    "speedLimit": 30,
    "distance": 4.2,
    "errorMessage": null
  }
}

4Move to bulk requests for whole journeys

Looking up more than one point? Use POST /Speed/bulk instead of looping single calls — see the endpoint reference below.

Authorization: Bearer <your_token>

Send this header on every request. A missing or invalid token returns 401 Unauthorized with a Problem Details error body — see Errors & Rate Limits.

GET /Speed

Returns the speed limit for a single coordinate.

Query parameters

Response fields (data)

The field that matters is speedLimit — that’s the primary data from our database. Everything else on this object (road name, class, IDs, distance) is supporting context gathered from Open Data rather than the primary result of this product.

Example — normal match

curl 'https://api.iw-slu.com/Speed?latitude=51.5074&longitude=-0.1278' \
  -H 'Authorization: Bearer <your_token>'

{
  "message": "Success",
  "error": null,
  "data": {
    "id": 184522,
    "longitude": -0.1278,
    "latitude": 51.5074,
    "overtureId": "3fa85f64-…",
    "fClass": "primary",
    "roadName": "Whitehall",
    "speedLimit": 30,
    "distance": 4.2,
    "errorMessage": null
  }
}

Example — outside the 20m buffer

curl 'https://api.iw-slu.com/Speed?latitude=51.3976&longitude=-0.10382' \
  -H 'Authorization: Bearer <your_token>'

{
  "message": "Success",
  "error": null,
  "data": {
    "id": 3375342,
    "longitude": -0.10382,
    "latitude": 51.3976,
    "overtureId": "9e7c7b2f-…",
    "fClass": "secondary",
    "roadName": "Brigstock Road",
    "speedLimit": 0,
    "distance": 21.01,
    "errorMessage": "The point requested is more than 20m away from any road in our network."
  }
}

POST /Speed/bulk

Returns speed limits for a list of coordinate pairs. Results come back paginated — each result uses the same fields as GET /Speed above.

Request body

Pagination fields (response)

Example

curl -X POST 'https://api.iw-slu.com/Speed/bulk' \
  -H 'Authorization: Bearer <your_token>' \
  -H 'Content-Type: application/json' \
  -d '{
    "page": 1,
    "pageSize": 100,
    "coordinates": [
      { "latitude": 51.5074, "longitude": -0.1278 },
      { "latitude": 53.4808, "longitude": -2.2426 }
    ]
  }'

{
  "message": "Success",
  "error": null,
  "data": [
    { "id": 184522, "roadName": "Whitehall", "speedLimit": 30, "…": "…" },
    { "id": 207781, "roadName": "Deansgate", "speedLimit": 20, "…": "…" }
  ],
  "pagination": {
    "total": 2, "page": 1, "pageSize": 100,
    "totalPages": 1, "hasNextPage": false, "hasPreviousPage": false
  }
}

Building a bulk request properly

Send coordinates as objects, not tuples. Each entry in the coordinates array needs explicit latitude/longitude keys — not [lat, lon] pairs or a flattened list.

"coordinates": [
  { "latitude": 51.5074, "longitude": -0.1278 },
  { "latitude": 53.4808, "longitude": -2.2426 },
  { "latitude": 55.9533, "longitude": -3.1883 }
]

Chunk large jobs into batches of 500. 500 pairs is the maximum accepted per request — split bigger jobs into batches rather than sending one large array. Think carefully about what you actually need in a batch: for example, eliminating the start or end of a journey, skipping lookups where speeds are below the minimum national speed limit for a country, or sampling at a lower frequency if appropriate.

function chunk(coords, size = 500) {
  const out = [];
  for (let i = 0; i < coords.length; i += size) {
    out.push(coords.slice(i, i + size));
  }
  return out;
}

Always check hasNextPage. The bulk endpoint paginates its response independently of how many coordinates you sent. Loop on pagination.hasNextPage until it's false, incrementing page each time, rather than assuming one call returns everything.

Match results by coordinate, not array position. The reference doesn't guarantee results are returned in the same order they were submitted. Match on the returned latitude/longitude rather than assuming data[i] corresponds to coordinates[i].

Problem Details error body

Every error response (4xx or 5xx) comes back in this shape (RFC 7807). The example below is illustrative to show the structure — the actual type/title/detail values for each error case aren't enumerated in the reference documentation.

{
  "type": "https://api.iw-slu.com/problems/unauthorized",
  "title": "Unauthorized",
  "status": 401,
  "detail": "Missing or invalid credentials.",
  "instance": "/Speed"
}