usporavati

1. (+ acc.) to slow down; to hold up
   Ova birokratija samo usporava ceo proces. — This bureaucracy only slows down the whole process.
   Stari program usporava računar. — The old program slows the computer down.
2. (intransitive; of processes with se) to slow down; to decelerate
   Voz usporava pred stanicom. — The train slows down before the station.
   Rast cena se polako usporava. — Price growth is gradually slowing down.

The perfective is usporiti. Of vehicles and people in motion it is usually used without se: voz usporava, auto usporava; of abstract processes more often with se: rast se usporava.