According to an airport police incident report, a Bombardier (LearJet) 35A had just landed, and was taxiing on taxiway A during night conditions. A witness reported that the tug was traveling south on an access road, and approaching the taxiway A stop sign. The witness added that the tug did not slow for the stop sign, traveled past it, and struck the nose of the airplane. The witness further stated that the stop sign had flashing red lights that were operating at the time of the collision. The airplane sustained substantial damage to the radome area, which required a major repair. The driver of the tug did not report any preimpact mechanical malfunctions with the vehicle. The recorded weather at the airport, about the time of the accident, included scattered clouds at 3,800 feet, and 8 miles visibility in light rain.