The approach of a land-falling hurricane before evacuation is completed may result in an order to stop evacuation. Large numbers of motorists ordered off highways may not have time to find formal shelters and shelters may not have capacity for large numbers of motorists. Multi-level above-ground parking garages may be used as “Refuges of Last Resort” to shelter these motorists when a hurricane evacuation is stopped prior to landfall. Our goal was to assess the relative safety of using a parking garage for this purpose through field work in a hurricane and a wind tunnel experiment.

Field work to determine the wind patterns inside a 7-floor parking garage was conducted at Norfolk, Virginia, on 18 September 2003 during Hurricane Isabel. The garage had openings on three sides, 1.1 m tall and 5.5 m to 8.5 m wide, and each parking level had an area of 5,065 m2.

Winds measured continuously outdoors on the roof gusted to 32 m/s and sustained winds over tropical storm strength occurred for six hours. Mean wind speed measured continuously inside the second floor garage, 6 m from upwind openings, was 26% of the outdoor mean. Gusts averaged 33% of outdoor gusts. The maximum gust at this indoor, upwind site was 12 m/s. Mean wind speed measured inside the second floor of the garage, 30 m from upwind openings and near the center of the garage, averaged 10% of the outdoor mean. Gusts averaged 16% of outdoor gusts. The maximum gust at this interior site was 7 m/s. Numerous one-minute wind measurements on a 44-point grid on the second floor of the garage showed wind gusts inside the garage were 10% to 20% of outdoor gust speeds in the interior core of the garage, 20% to 30% of outdoor gust speeds through most of the garage, and over 30% of outdoor gusts within one parking space (6 m) of the upwind openings of the garage.

These field results were supported by results from the testing of a model parking garage in a wind tunnel. Motorists inside a vehicle using a parking garage as a “Refuge of Last Resort” are relatively safe, with respect to wind, even in a strong hurricane.