liikennelaitos

Noun

 * 1) A municipal or regional authority responsible for providing public transportation in its area of operation. There's an ample supply of English equivalents, such as transit authority (New York), transit commission (Toronto), public transport authority (Western Australia).

Usage notes
Some "official" translations of Finnish public transport authorities:
 * City of Helsinki: Helsinki City Transport
 * Helsinki region: Helsinki Regional Transport Authority
 * Tampere: Tampere City Transport
 * Turku: Public Transport Office (of Turku)