Given that road bikes are generally faster and lighter I wonder why police, much like their use of HDs, choose to use mtbs? The only real advantage a mtb has for the most part is adeptly handling rough terrain. Road bikes accelerate faster being that their usually less than half the weight of a mtb and SS's are nearly silent in operation which in tactical operations would be a distinct advantage. Although the harsh ride of the rigid frame would make a full (8hr) shift very fatiguing.
Obviously, you have never tried to ride a road bike while wearing a ballistic vest and a belt with 20lbs of gear on it.