Road511
Unified traffic data from 65 US/CA jurisdictions: events, cameras, signs, bridges, truck routes
Travel Search - Limited usage.
Sabre for Developers API is a free Transportation API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Access powerful travel APIs, SDKs, and tools to build airline, hotel, and agency solutions. Get integration guides, documentation, and expert support for seamless development.
Details from developer.sabre.com.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
Unified traffic data from 65 US/CA jurisdictions: events, cameras, signs, bridges, truck routes
Provides safe restroom access for transgender, intersex and gender nonconforming individuals
Irish Rail planned engineering works: affected stations, DART closures, change log and ICS feeds
Yes. The Sabre for Developers API is listed in the Transportation category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Sabre for Developers API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Sabre for Developers API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Sabre for Developers API is served over HTTPS, so it's safe to use in production.