US Department of Transportation · Rate Limits

Dot Rate Limits

DOT agency APIs do not publish hard per-minute or per-hour rate limits in their public documentation. FMCSA QCMobile and SaferBus APIs are protected by a webkey requirement; result sets are capped at 50 carriers per response page. NHTSA vPIC implements an automated traffic rate control mechanism to ensure optimal performance but does not specify numeric thresholds publicly. NHTSA vPIC batch VIN decode supports up to 50 VINs per request and paginates at 100 items per page. The DOT Open Data Portal is governed by Socrata/Tyler platform rate controls. Reasonable use and exponential backoff on 429/503 responses are expected across all services.

Dot Rate Limits is the machine-readable rate-limit profile for US Department of Transportation on the APIs.io network, conforming to the API Commons Rate Limits specification.

It captures 5 rate-limit definitions, measuring carriers_per_response, vins_per_batch_request, items_per_page, and requests_per_minute.

The profile also includes 4 backoff/retry policies defined and response codes documented for throttled, quotaExceeded, unauthorized, badRequest, notFound, serverError, and serviceUnavailable.

Tagged areas include Rate Limiting, Government, and Transportation.

5 Limits Throttle: 429 Quota: 429
Rate LimitingGovernmentTransportation

Limits

FMCSA QCMobile — results per page request
carriers_per_response
50
When the API returns data on more than one carrier, results are limited to the first 50 carriers. Use the start and size query parameters to paginate.
NHTSA vPIC — batch VIN decode request
vins_per_batch_request
50
The DecodeVINValuesBatch endpoint accepts a maximum of 50 VINs per POST request.
NHTSA vPIC — pagination page size query
items_per_page
100
Paginated NHTSA vPIC endpoints return up to 100 items per page. Use the page query parameter to retrieve subsequent pages.
NHTSA vPIC — traffic rate control IP
requests_per_minute
not publicly documented
NHTSA vPIC states that users will be controlled by an automated traffic rate control mechanism. Specific thresholds are not published; implement exponential backoff on 429 responses.
FMCSA — general fair use account/key
requests_per_minute
not publicly documented
FMCSA does not publish explicit numeric rate limits. API webkey authentication is enforced; authentication failures return a 401 JSON error. Reasonable fair-use limits apply.

Policies

WebkeyAuthentication
FMCSA APIs require a webkey query parameter on every request. Register for a free developer account at mobile.fmcsa.dot.gov and authenticate via Login.gov to obtain a webkey. Do not share or expose your webkey in public repositories.
ExponentialBackoff
On 429 or 503 responses, retry with exponential backoff and jitter. Honor any Retry-After header when present.
Pagination
FMCSA endpoints accept start and size parameters for pagination. NHTSA vPIC uses the page parameter. Always page large result sets rather than relying on a single oversize query.
BulkDownloads
For large data extracts, prefer bulk download files from the DOT Open Data Portal (data.transportation.gov) over repeated API calls against the live query endpoints.

Sources