It will teleport in through a big I.D.P.D. portal, breaking walls and running over everything in its path including walls and other enemies. It only deals contact damage while moving and can be damaged by enemies that aren't a part of the I.D.P.D.
After a short distance the Van will stop and unload I.D.P.D. troops, staying stationary after unloading. When destroyed it creates three I.D.P.D. grenade-like explosions and drops up to 3 ammo/health pickups. It can be destroyed while it's moving which will prevent it from unloading troops.
Vans don't have to be destroyed to finish a level. The level ending portal will open even if you leave a Van undamaged.
Getting in the van and pressing "E" while it's unloading I.D.P.D. units will teleport you to the I.D.P.D. HQ secret area.