BANGOR, Maine — Keeping watch over the more than 100,000 people expected to attend this weekend’s American Folk Festival is no easy feat.

After all, festival-goers are spread out over most of the 36 acres that make up the city’s waterfront area.

In the past three years, however, the job has gotten easier, thanks to the city’s mobile command center, one of four such vehicles the Maine Emergency Management Agency purchased in 2005 — at a cost of $331,500 each — with federal homeland security funds.

Since then, the city’s vehicle, which is housed at the Central Fire Station on Main Street, has undergone tens of thousands of dollars’ worth of upgrades and enhancements.

“It would cost about half a million dollars to replace it,” Bangor fire Capt. Tom Higgins said Friday, less than two hours before the folk festival’s 6 p.m. kickoff.

The command center on wheels will serve as the headquarters for the city police officers, firefighters and bicycle paramedics whose job it is to keep people safe during the three-day festival, which runs through Sunday.

The 41-foot-long vehicle is equipped with such bells and whistles as a computer-aided dispatch console; portable radios; ham, marine and aviation radios; a satellite phone; a satellite television for monitoring breaking news; a weather station; spotlights; eight laptop computers; and a 900-megahertz mobile data station.

According to Higgins, the communications gear inside the mobile command center is fully interoperable, which means it has radio coverage across the spectrum band and the ability to interface digital with analog communications.

That also means people staffing the command center can communicate with all of the other public safety agencies they may need to consult in case of a major emergency.

“Anything we can do at the police station we can do here,” Deputy Police Chief Peter Arno said Friday.

Another feature is a 40-inch LCD screen with a smart board that allows emergency personnel to map out actions, connected to a camera that can telescope up to 20 feet above the roof to provide a bird’s-eye view. The camera can scan the festival grounds as well as zoom in for closer views, Higgins said.

Though there were no plans to use it this weekend, the vehicle also has a larger, outside projection screen on its side in the event that a large group of people needs to be briefed on an incident or event.

During past festivals, the unit was set up next to the Bangor harbor master’s building on Front Street. This year the vehicle was moved downriver to the vendors area to be more centrally located, Arno said.

The inside of the unit is divided into three sections. Up front is the communications area. In the back is the command center, which also serves as a conference room. In between is a small galley and restroom. Each section can be closed off if necessary.

Maintaining public safety and peace during events such as festivals and fairs is only one aspect of what the unit is used for. Higgins said that the unit went to Fort Kent for the major flooding there in April 2008.

The state police used it during their investigation of the murder of two sex offenders on Easter Sunday 2006. The unit also was in Hampden this spring during the initial search for a missing teenager who later was found dead, he said.