That's a keen idea. Did you write them up like a faction, with hierarchy and goals and the like? I can see that being pretty interesting as well.
I'm in New York, so I based them--loosely--on the NY State Police. Squads of Wardens (6-8) commanded by Sergeants, are organized into Troops (4-6 squads) commanded by Lieutenants. Two or three Troops form a Barracks, responsible for a Region, and commanded by a Captain. Funded by the Merchants' Guilds and the various duchies and baronies through which the roads run, their goal is to protect travelers and keep the trade routes open.
Since they're chronically understaffed, they're usually willing to recruit PCs for short or long-term employment.