Texas hurricane evacuation study.

This report evaluates the ability of the existing highway system to accomodate the evacuation of people from the Texas Gulf Coast barrier islands prior to landfall of a hurricane. Unfortunately, the state of the art in predicting characteristics of storms necessary to evaluate the transportation system capacity is not sufficiently definitive to make categorical statements concerning hurricane evacuation. Nevertheless, there is sufficient evidence to indicate that an evacuation problem may exist on all the Texas barrier islands because roads may flood before people are aware of a potential storm. The probability of occurrence of this problem, however, is unknown. The available data base is sufficiently definitive to provide a reasonable estimate of the number of permanent residents and the maximum number of vehicles that permanent residents have available for evacuation. It is also possible to estimate the minimum time it would take to evacuate those permanent residents and their vehicles. The study did not include consideration of tourists because no data existed to indicate when they might leave, or whether they might come during the threat of a hurricane. It was, therefore, assumed that tourists would leave in advance of the critical time period. If tourists need to be evacuated, evacuation times would increase. The study indicated that winds of 50 mph and gusting to 75 mph can exist 10 to 20 hours prior to landfall of a hurricane. Since, winds of this magnitude can overturn trucks, motor homes and vehicles with trailers, consideration should be given to prohibiting these vehicles on the highways upon issuance of a hurricane warning. This would undoubtedly require special legislation. Further data and study are needed in several areas. As a result of subsidence, precise elevations along IH-45 are unknown. The study shows that evacuation may be possible if the elevation at which the roadway was constructed still exists. The barrier islands, other than Galveston Island, all have critical roadway elevations in the range of four feet. Better data are needed to determine when, with what probability, and with what types of storm tides might reach 4 feet. If 4-foot tides occur with high probability 18 to 36 or more hours prior to a storm, as suggested by the National Weather Service, total evacuation of the barrier islands is not possible, given existing roadway conditions storms and forecasting techniques. The resulting alternatives are: 1) improve storm forecasting procedures; 2) change the roadway elevation; and 3) protect people on the island during the storms rather than attempt evacuation. Each of these alternatives warrants further consideration.