My way to survive in survival mode: Find a nice walled parking lot, or something, that only has one entrance. Put all police in it. Come out years later when the apocalypse is over, along with any citizens smart enough to stay in the safe room.
COME ON! On level 7 i waited patiently for a minute then ran out and knifed the guy,getting shot and triggering a alarm,then i ran and hid,got found just after the alarm ran out and shot twice but survived,got to an inch away from the manhole then a guard turned around and shot me again finishing me off.