I have approached to OpenStreetMap service for scientific research purposes. In particular, I would need speed limits on various GPS points, and for this reason, I am using OpenStreetMap API. Is there a way to not get blocked if I send numerous requests all from the same terminal?
Don’t use the API. Download the data, load it into a database, and query that.
https://planet.openstreetmap.org/ has links to lots of mirrors and extracts - I suspect you’ll initially want to use a small portion of the data, so see https://wiki.openstreetmap.org/wiki/Planet.osm#Country_and_area_extracts .
Perfect! Thank you very much for the help. Do you have any advice for me about this operation?
The easiest way is to import into PostGIS using osm2pgsql (note this is lossy, specifically in your case it removes the graph of the road network) but it keeps geometry & you can configure it to ensure the tags who want are accessible (use hstore option). You can also, for instance, only highways.
There are other formats, but they tend not to support rebuilding some complex geometries.