Just to give an possible answer to this, if civilians find road barriers, spike strips etc laying around, they will deploy them on the middle of roads and in dangerous turns to surprise people passing by, and there is no reason to blame cops for doing it, I have seen many medics trying to block of roads because they respond to someone who's dead on the side of the road.
Back to what I wanted to say, Medics carry them, some cops carry them, if the manage to crash their vehicles and die, or are getting killed some civilians or rebels will pick these items up.
BUT, if cops are deploying any of these things, and aren't cleaning it up, it will be taken up in the next meeting. (sometimes cops do loose firefights, leading to spike strips or other objects being on the roads)