Highway Patrol frequencies
The Volvo cruisers are but a distant memory now. most visible cruiser used is still the Ford Crown Vic, followed by the Chevrolet Impala. Most departments also have at least one four wheel drive, usually a Ford Explorere or maybe a Chevy Tahoe.
Highway Enforcement, now technically known as Highway Patrol (different organization than the New Hampshire State Police) use the appropriate New Hampshire State Police Troop frequency for the area of the State they are patrolling in. Their call signs are numeric, preceeded by the prefix of "MV", as in "MV 11". A trooper will just use his numeric call sign, such as "123" with no prefix.
To monitor, you will need an APCO 25 digital capable scanner programmed to the Troop Stations you wish to listen. All Troop Stations use repeaters, so you will be able to monitor Troop to unit and unit to unit transmissions with ease, unless units swith to "talkaround".
The fordyce site annotated in a previous post has the frequencies and locations of all the various Troop dispatch sites in New Hampshire.....
Good luck....