Our previous research has shown that common passenger vehicles are at risk of upset by winds above 115 mph (BAMS 83:1821-1830) on the vehicle. Additional tests were conducted to determine the minimum wind speeds for upset of two types of ambulances and a city bus so that guidelines can be established for their safe operation during a hurricane. Models were tested with a six-component external balance in a commercial grade wind tunnel with cross section 2.1 m by 3.0 m. Resultant loads were measured over a 180 degree yaw sweep.

The minimum wind speed for upset of a Type I ambulance (9,100 kg weight) was 145 to 155 mph with winds angles of 35 degrees to 140 degrees as measured from the front, and higher at other wind angles. For the Type II ambulance (4,300 kg), the minimum wind speed for upset was 155 mph at a wind angle of 40 degrees, and 170 to 200 mph for other wind angles. For a loaded city bus (14,600 kg), the minimum wind speed for upset was 65 to 70 mph over the wind angles of 45 degrees to 140 degrees on the vehicle. Considerations of driving speed, risks, and needs for transport can be used to develop safe wind speeds for operating these vehicles.