DURHAM, N.C. — In an apparent protest of the G-8 Summit in Georgia, Durham police say someone hung signs from Interstate 40 and Durham Freeway overpasses stating the Research Triangle Park was quarantined Thursday morning.

Police say a group of masked men then orchestrated the closing of at least three railroad crossings running through RTP.

"They found someone had rigged the arms on the railroad crossings to come down and that some explosive-looking device was also found in the area. Since then it has been determined that the explosive device was nothing more than some type of fireworks and has been rendered safe," said Lt. Norman Blake of the Durham Police Department.

Those fireworks were retail-bought smoke bombs, according to police. A section of Cornwallis Road between Davis Drive and Miami Boulevard was closed as police investigated.

Dr. Roger Cannon, of the nearby U.S. Army Research Office, says the impact of the threat was minimal.

"Our facility was not affected at all. The only problem was inconvenience for some of the employees coming to work at that time of the morning. It had about the same impact as a traffic jam or an accident on the road," he said.

The investigation tied up traffic and local agencies, including police, the Durham County Sheriff's Office, hazardous materials and bomb squad teams.

Hazmat crews checked out containers left behind with an unknown liquid.

Witnesses reported seeing a white Chevy truck with a camper leaving the scene. If caught, the suspects could face serious charges, possibly federal charges, for tampering with railroad crossings.