It was a contractor for US, no injuries, except to the aircraft. That crossing is used quite alot at night by US people coming and going to the hangar...There was a US employee that witnessed the incident, and he told the APD that the stop lights were flashing when the accident happened. One possibilty is when those check runners are taxiing to the FBO they do taxi down A at a hight rate of speed, so by the time the aircraft activates the underground loop they are right up on the roadway crossing. We went out at 0500 and double checked the lights and they were indeed functioning...