Police-escorted convoy of trucks down Flatbush lately after midnight?

From my apartment on Sterling Place, a number of times recently I have heard the police saying something by electronic megaphone, followed by what appears to be a convoy of large trucks interspersed with several police cars proceeding south on Flatbush (i.e., away from Manhattan).  I can't see everything because I'm at the tree line, but it's clear these are oversize trucks surrounded by flashing police cars.  I'm just curious -- what are these carrying, and where to?  I'm assuming it's a large apartment complex being built or some other large structure.