The airplane was taxiing for takeoff on a 50-foot wide taxiway. The flightcrew observed an airport vehicle parked on the grass, off the right side of the taxiway. The flightcrew also observed a larger airplane that had taxied past that point, and thought the clearance was adequate. However, as the airplane continued to taxi, the right wing struck the rear of the airport vehicle. A safety area extended an additional 34 feet from the edge of the taxiway. The driver of the airport vehicle parked about 6 feet from the edge of the taxiway; about 28 feet in the safety area. The driver did not inform air traffic control that the vehicle was parked there, and buildings obstructed the view from the control tower. Probable Cause: The flightcrew’s misjudged clearance from a parked airport vehicle while taxiing. A factor was the vehicle operator’s improper decision to park within a taxiway safety area.