The open API for building cool stuff with transport data.
Navitia API is a free Transportation API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Details from doc.navitia.io.

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.
Bike, scooter, motorcycle, wheelchair and walking routes across Europe, with safety indicators
The Navitia API is provided by Navitia.io documentation (doc.navitia.io).
Yes. The Navitia 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 Navitia API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Navitia API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Navitia API is served over HTTPS, so it's safe to use in production.