It is also recommended that a least some of the aerobic workout be done on a track instead of a treadmill or bike. This is to help train as specifically as possible for the timed 1.5 mil run for the police department test. A person's initial level of fitness will determine how much training they should undertake in the beginning. Let your body be your guide. Injuries occur at greater rates when running outdoors and at greater frequencies and intensities.
Slow progression is the key to successful training.