Hurricane Evacuation Studies

In March 1994 the National Hurricane Program Task Force was established to assist the Federal Emergency Management Agency (FEMA) with planning an enhanced Hurricane Program. Several work groups were formed within the Task Force to address proposed components of that program. Since, for several years, the preexisting Interagency Coordinating Committee on Hurricanes (ICCOH) had managed hazards analysis, population preparedness, and post-storm analysis issues related to the Population Preparedness Project (Hurricane Evacuation Study) phase of FEMA's Hurricane Program, that committee was asked to function as a Task Force work group for those topics. To support the work of the ICCOH, Headquarters, U.S. Army Corps of Engineers (USACE) subsequently organized the Hurricane Evacuation Studies Technical Guidelines Working Group.

USACE Study Managers, FEMA Regional Hurricane Program Managers, the National Weather Service, the American Red Cross, and state and local governments were represented on the Working Group and its task forces. The Working Group was charged with examination of a variety of issues related to the execution and use of Hurricane Evacuation Studies (HES). Members were instructed to provide, where appropriate, recommendations for innovations or improvements.

These revised guidelines, an update of the November 1984 guidelines produced by the Jacksonville District, USACE, resulted largely from the HES Technical Guidelines Working Group's efforts. This document was prepared by the Wilmington District's Flood Plain Management Services Branch on behalf of Headquarters USACE and in support of the ICCOH and the National Hurricane Program Task Force. It has been fully coordinated with FEMA. The methodologies described herein are based on previous HES procedures and recommendations to the ICCOH by the HES Technical Guidelines Working Group. They are intended as a flexible framework within which USACE Study Managers can effectively develop important basic information and translate it to local officials. The study process includes methods of applying the information in formulating preparedness plans and of educating the public to hurricane hazards and evacuation procedures. Broad use of these guidelines should provide uniformity of terminology and content to a complex study process. While these guidelines were prepared to assist USACE Study Managers, they may be useful to other agencies managing HES or components of studies.

INTRODUCTION

a. U.S. Army Corps of Engineers (USACE).

Allocation of USACE resources for planning activities related to hurricane preparedness is authorized under the Flood Plain Management Services (FPMS) Program, established by Section 206 of the 1960 Flood Control Act, as amended. In order for the USACE to manage a Hurricane Evacuation Study (HES), a written request must be received from the chief emergency management officer or higher of a state.

b. Federal Emergency Management Agency (FEMA).

Through Executive Orders 12148 and 12673, FEMA is assigned primary Federal responsibility for carrying out the functions of the Robert T. Stafford Disaster Relief and Emergency Assistance Act of 1988 (Public Law 93-288, as amended). Under this authority, FEMA administers the Hurricane Program. FEMA authorization for HES funding requires an application from the governor or the chief emergency management officer of a state.

c. National Oceanic and Atmospheric Administration (NOAA).

(1) NOAA's National Weather Service (NWS) contributes to the HES program through the Techniques Development Laboratory (TDL) and the National Hurricane Center (NHC). In addition, the Atlantic Oceanic and Meteorological Laboratory (AOML) provides staff support to the NHC for the studies. Using NWS funds, the TDL develops the Sea, Lake, and Overland Surges from Hurricanes (SLOSH) numerical models that are the basis for each study. Partly with outside funding, the NHC makes the hundreds of SLOSH computer runs that are necessary to define the hurricane threat for each evacuation study area. NWS officials, especially Meteorologists in Charge (MIC) and Warning Coordination Meteorologists (WCM) of local NWS offices, have made substantial contributions to evacuation studies by actively participating in public meetings and by serving as consultants to the study managers.

(2) Through its Coastal Zone Management Program (CZMP), NOAA's Office of Ocean and Coastal Resources Management (OCRM) is authorized to provide funds to appropriate state agencies for hurricane preparedness. Under this program, application may be made by the state to OCRM for hurricane evacuation study funding.

d. Other Study Participants.

Other Federal, state, and local agencies should be encouraged to actively participate in Hurricane Evacuation Studies to the greatest extent possible, including sharing in the study costs by providing cash contributions and/or contributory services. Agencies that should be considered include the following: state emergency preparedness and coastal management organizations; state departments of transportation; military installations; and the American Red Cross. A state may seek funding support from local governments and organizations (e.g., regional planning agencies, development commissions, etc.) and the private sector. States also may use available Federal program funds.

OBJECTIVES

The overall objective of an HES is to provide emergency management officials with state-of-the-art information on the major factors affecting hurricane evacuation planning and decision-making, and the skills and training aids necessary to educate the public.

An HES should be comprehensive in scope and multi-regional in perspective; analyses should cross state boundaries where necessary. This approach will ensure that the need for interaction among the various evacuating jurisdictions during a hurricane threat will be recognized. Where traffic and/or sheltering concerns will affect locations far removed from the evacuation area, state-wide studies should be considered. The technical data produced in a hurricane evacuation study should be presented in a documented report suitable for use by public officials in preparing or updating evacuation plans. The data should also aid in developing operational procedures and decision guides for future hurricane threats.

The methodology of an HES should encourage cooperation between local emergency management officials, their state counterparts, local NWS officials, the NHC, the American Red Cross, the local news media, and other agencies and organizations involved in hurricane preparedness and evacuation. Close coordination between these agencies will facilitate more effective responses at the local level to hurricane emergencies. The end result should be a prepared government and an informed public.

MANAGEMENT

Flood Plain Management Services units at USACE district offices normally conduct HES and assign one person as the USACE Study Manager. Selection of a Study Manager is one of the most important issues to be decided at the outset of an evacuation study. Successful management of an HES requires a firm commitment by the USACE district to provide significant manpower, contract and administrative support, and other resources over at least a three year period..

PLAN OF STUDY

a. Purpose.

The plan of study contains the basic descriptions of work and cost estimates that govern the overall conduct of the HES. It should be a useful tool for the Study Manager, allowing flexibility by describing the desired products of the major study tasks and, to the greatest extent practicable, leaving the means of producing those products to his/her discretion.

b. Development.

Before FEMA can authorize funds for an HES, a state must submit a written application to the appropriate FEMA Regional Director. A plan of study must be submitted by the state as part of its application, but it does not necessarily have to accompany the initial correspondence. If the USACE is designated the project management agency, the Study Manager should coordinate with the FEMA Program Manager and submit a draft plan for USACE Division approval.

Prior to completion of the draft plan, one or more plan of study development meetings should be held with appropriate Federal, state, and local officials, and persons having technical expertise in fields related to the study.

c. Contents.

The following points should be addressed in a typical plan of study. Descriptions should be concise and allow flexibility of execution.

(1) Purpose. Describe the purposes of the plan of study.

(2) Study Objective. Describe the objective of the HES.

(3) Study Description. Describe the study area, specific problems to be addressed, and study procedures.

(4) Scope of Work. The scope of work should contain a description of the proposed conduct of the study, including in-house effort, contracted services, in-kind services provided by all participating agencies, and coordination procedures. Also, a description of study methods outlining all technical evaluation and analysis procedures and reports should be included. Maintain flexibility to greatest extent practicable. A detailed scope of work may be included in the plan of study as an appendix.

(5) Summary of Deliverables. This summary is principally a narrative describing study products scheduled at predetermined milestones in the study. Availability of that data indicates the completion of specific study tasks.

(6) Study Schedule. A chart or diagram showing, by month, scheduled and actual work sequence, progress, and task completion dates for the entire study period.

(7) Cost Summary. An estimated cost for each major task or analysis, and an estimated total study cost.

The Study Schedule and the Cost Summary are working documents that should be periodically updated.

STUDY TASKS

a. General.

The HES process has evolved into what is presently a series of five major analyses that are interrelated and conducted in an efficient, logical order. The hazards, vulnerability, behavioral, shelter, and transportation analyses develop technical data concerning hurricane hazards, vulnerability of the population, public response to evacuation advisories, sheltering needs, and timing of evacuations for a range of hurricane threat situations. As the study progresses, some analyses produce data upon which subsequent analyses are based.

Generally, study coordination is the first task initiated and begins with the development of the plan of study and the organization of the Disaster Preparedness Committees.

The final products of an HES are the information contained in the technical data report and its appendices and any maps, charts, diagrams, decision-making tools, or other study products that will enhance the usefulness of the data developed in the study.

Several study products lend themselves well to computer formats, which can greatly enhance their presentation, reduce the chance of error when manipulating data under stressful circumstances, and lower the costs of revisions and updates.

b. Coordination.

A hurricane evacuation involves several governmental agencies and private organizations performing such functions as storm warning, evacuation decision making, communications, traffic control, and shelter management. These agencies and organizations also have an indispensable role in hurricane preparedness planning.

The ultimate decision to evacuate an area is usually left to the elected officials in charge of that jurisdictional unit, who are advised by the local Director of Emergency Management. Since those officials are held responsible for hurricane evacuation planning and decision making, it is especially important that they are familiar with the study from its outset; however, they seldom seek involvement with the study process or products.

The close coordination that is necessary to a successful HES poses a challenge to the study manager. For previous studies, a tri-level coordinative mechanism has been used to provide maximum flexibility, ensure proper and thorough data gathering, and allow

for unencumbered exchange of information. A description of the traditional coordinative structure follows:

(1) Interagency. Communication between the Federal, state, and local agencies involved with the study should be unencumbered. The Study Manager should keep all Federal and state agencies abreast of the progress of the study through frequent oral communication and formal status reports.

(2) Disaster Preparedness Committees. The Disaster Preparedness Committees should consist of state and local emergency management officials, local elected officials, the local NWS office, the American Red Cross, and key personnel of other agencies and organizations, primarily at the county, township, and city level, who have direct responsibility and authority in some aspect of hurricane emergency operations or planning. The primary purposes of the Disaster Preparedness Committees are to provide important data for the study and to review appropriate study products.

(3) Executive Committee. Officials from the principal participating agencies should be asked to serve as members of the Executive Committee. Membership should include an appropriate USACE official at division level, a designated representative of the FEMA Regional Director, and a representative of the state requestor. The Executive Committee should convene as needed to review the progress of the study, to discuss and plan for future study tasks, and to ensure the interagency coordination that is vital to the HES effort.

c. Hazards Analysis.

(1) Hazards of Coastal Storms. The purpose of the hazards analysis is to quantify the wind speeds and still-water surge heights that could be produced by a combination of hurricane intensities, approach speeds, approach directions, and tracks considered to have a reasonable meteorological probability of occurrence within the study area.

(2) Storm Surge. Storm surges are higher than usual water levels along coastlines and the shorelines of bays and estuaries that result from large-scale meteorological disturbances. As the wind blows over the surface of the water, it exerts a horizontal force that induces currents in the same general direction. These currents are the primary cause of storm surge.

(3) Wind Hazards. Although most casualties of hurricanes and extratropical storms are victims of storm surge, wind hazards accompanying these storms are not to be ignored. Hurricanes Hugo (1989) and Andrew (1992) have demonstrated the widespread devastation often caused by violent winds in intense storms. Recently, NOAA's Hurricane Research Division has developed a model for predicting inland winds associated with landfalling hurricanes along the Gulf of Mexico and the Atlantic coast as far north as North Carolina. A similar model is expected to be forthcoming for the mid-Atlantic states. This model accounts for wind speed decay as hurricanes move over land from the water.

(4) Forecasting Errors. Hurricane (and extratropical storm) forecasting is not an exact science. An analysis of hurricane forecasts made by the NHC indicates the normal magnitude of error.

SAFFIR/SIMPSON HURRICANE SCALE RANGES

Scale

Number Central Pressure Winds Winds

Category Millibars Inches (Mph) (Kts) Damage

1 > 980 28.94 74 - 95 64 - 83 Minimal

2 965 - 979 28.50 - 28.91 96 - 110 84 - 96 Moderate

3 945 - 964 27.91 - 28.47 111 - 130 97 - 113 Extensive

4 920 - 944 27.17 - 27.88 131 - 155 114 - 135 Extreme

5 < 920 < 27.17 > 155 > 135 Catastrophic

(5) The SLOSH Model. The primary objective of the hazards analysis is to determine the probable worst-case effects from the various intensities of hurricanes that could strike the region. The study identifies "worst-case effects", i.e., the peak surges, wind speeds, and wave effects that can be expected at all locations within the study area, regardless of the point of hurricane landfall. The NHC uses the SLOSH numerical model to determine the timing, severity, and sequence of wind and storm surge hazards that can be expected from hurricanes of various intensities, tracks, and forward speeds striking the study area, computing the potential effects of many hundreds of theoretical hurricanes.

(6) Maximum Envelope of Water. Effective evacuation planning and decision making require a means of compensating for inaccuracies in hurricane track forecasting. The Maximum Envelope of Water (MEOW) developed by the NHC provides a good form of condensation by eliminating any consideration of hurricane track. Coincidentally, the MEOW greatly simplifies the planning and decision-making processes by reducing the number of variables that must be considered.

(c) Wave Effect. The SLOSH model does not provide data concerning the additional heights of waves generated on top of the still-water storm surge. Generally, waves do not add significantly to the total area flooded by storm surge and can usually be ignored, except for locations immediately along the open coastline or the shorelines of very large sounds and estuaries. In these areas, wave crests can increase the expected still-water depth above the terrain significantly, greatly increasing the hazard. High velocity "V Zones"

Program (NFIP) where waves higher than three feet with a one percent annual chance of occurrence are expected.

(9) Time-History Data. In the SLOSH model, up to 120 geographic "critical points" can be designated for time-history tabulations of surge height and wind speed that are valuable in hurricane preparedness planning. These tabulations can be used for timing evacuations, sheltering, and traffic control. "Critical points" are usually selected at a special meeting of NHC and emergency management officials prior to commencing the SLOSH model storm simulations. They are chosen to coincide with locations where flooding would probably first curtail an evacuation, low-lying roads and bridges; at potentially vulnerable population centers; and at significant natural or manmade barriers..

(10) Rainfall Flooding. Potential freshwater flooding from rainfall accompanying hurricanes must also be evaluated. However, due to the wide variation in amounts and times of occurrence from one storm to another, rainfall can only be addressed in general terms.

(11) Extratropical Storms. Where appropriate, hurricane evacuation studies should address extra-tropical storms. The historical severity of "nor'easters" in the mid-Atlantic and New England states necessitates including them in any treatment of coastal storms.

(1) General. The purpose of the vulnerability analysis is to identify the areas, populations, and facilities that are potentially vulnerable to flooding and extraordinary wind damage under a variety of hurricane threats.

(2) Inundation Maps. The purpose of the inundation maps, sometimes called storm surge atlases, is to depict the limits of the potential flooding from the peak surge values computed by the SLOSH model. The primary use of these maps is to determine which surge vulnerable areas may need to be evacuated in response to a particular coastal storm threat.

(3) Vulnerable Population. The vulnerable population is comprised of all persons residing within the area subject to storm surge and the residents of mobile homes located above expected flood levels. It is important to note the special provisions for those living in mobile and manufactured homes. Because of their greater vulnerability to the strong winds associated with hurricanes, all mobile and manufactured home residents are advised to evacuate regardless of their location within the study area.

(4) Evacuation Scenarios. Hurricanes with quite different parameters can have virtually the same flooding impacts on a community. The hurricane evacuation scenarios depict the similar effects of unlike hurricanes. The scenarios are combinations of MOM's (hurricane intensity, approach direction and forward speed) that affect essentially the same population, delineating successive additional areas that will need to be evacuated. Following the initial development of the MOM's for the inundation mapping, further combinations of hurricane parameters are possible based on population distribution. Combinations that involve small population percentage changes may be appropriate. Care should be taken to ensure that the final scenario delineations accurately reflect the operational intentions of local emergency management officials by describing the areas that the community will evacuate concurrently.

(5) Evacuation Zones. A network of zones must be established that covers the entire study area. The purpose of evacuation zones is to geographically locate and quantify the vulnerable population, provide a base to model traffic movements from one geographic area to another, determine needed shelter capacity, and facilitate future updating. Since wind-vulnerable housing units will be quantified, evacuation zones should subdivide the areas above expected flood heights as well as those covered by the inundation scenarios.

(6) Institutional and Medical Facilities. Evacuation plans should include detailed information on the vulnerability of institutions and medical facilities to hurricane hazards. The purpose of this analysis is to determine the institutions and medical facilities that will require evacuation under various hurricane threats. Primary considerations include their proximity to vulnerable areas, exposure to extreme winds, and inundation of access routes.

(7) Public Transportation Demand. To the extent possible, population data developed for each evacuation zone should include an estimate of the numbers of persons who do not have access to a private vehicle and, consequently, would have to rely on public transportation in an evacuation.

(8) Special Emergency Transportation Needs. While transportation for the elderly and infirm residing in Special Needs (health-related) facilities should be the responsibility of the individual facilities, provision of adequate special emergency transportation for those in private homes is usually a responsibility of local emergency management officials. Institutions should be encouraged to develop comprehensive, coordinated hurricane evacuation plans that include when to leave, specific destinations, and pre-arranged transportation.

(1) General. In preparing hurricane evacuation plans, assumptions must be made regarding the manner in which the population in and around the vulnerable area will react to the threat. These assumptions are necessary for shelter planning, transportation modeling, and guidance in evacuation decision-making and public awareness efforts. The results of the behavioral analysis should be expressed in standardized terms to provide direct, compatible input for the transportation analysis.

(2) Objectives. The specific objectives of a behavioral analysis are to determine the following:

(a) The percentage of the vulnerable and nonvulnerable population that will evacuate under a range of hurricane threat situations. It is known that a number of people who have substantial housing and are not threatened by flooding will evacuate along with the vulnerable population.

(b) When the evacuating population will leave in relation to an evacuation order or advisory given by local officials or others in authority.

(c) The probable destinations of the evacuees, expressed as percentages of the total number, who would go to local public shelters, remain in the local area with friends or relatives, remain in the area in a hotel or motel, or leave the area for out-of-region shelter.

(d) The percentage of available vehicles that the evacuees will use for hurricane evacuation.

(e) The percentage of the total number of evacuating vehicles that may be motor homes or towing boats, campers, or other equipment.

(f) How the population will respond based on forecasts of hurricane intensity, probability, or other information provided during a hurricane emergency.

(h) The percentage of evacuees who would require public assistance for emergency transportation.

(3) Burden Hour Authorization. Estimates of the number of hours the public would be burdened by answering questions for the behavioral survey must be submitted to the Office of Management and Budget (OMB) through HQUSACE and FEMA.

(4) Effective Communication. Because of the substantial variation in the public's reaction to hurricane threats based on their perception of the specific circumstances and the advice of local officials, technical data reports should highlight the importance of effective communication of evacuation orders and advisories in prompting appropriate public response.

(1) General. The purposes of the shelter analysis are to estimate the number of evacuees that will seek public shelter and the number of shelter spaces available, and to provide information for use in determining evacuation clearance times in the transportation analysis. The shelter analysis should address shelter locations,

capacities, demand, and potential vulnerability. Data developed in the hazards, vulnerability, and behavioral analyses are used in the shelter analysis.

(2) Public Shelter Inventories and Capacities. The Study Manager should request an inventory of existing public shelters and capacities from the appropriate state or local agency.

(3) Potential Vulnerability. The Study Manager should locate the public shelters on the inundation maps, asking local emergency management, department of social services, or American Red Cross officials for assistance, if necessary. He/she should then determine the vulnerability of those shelters and their access routes to flooding.

(4) Public Shelter Demand. Public shelter demand (number of evacuees seeking public shelter) should be calculated for each evacuation scenario. Calculations should be based on population data developed in the vulnerability analysis and estimates of the percent of evacuees seeking public shelter established in the behavioral analysis.

(5) Demand/Capacity Analysis. For every community in the study area, the shelter demand generated by each scenario and tourist situation should be compared to the total available shelter capacity.

(6) Shelter Assignment. Following completion of the transportation analysis, each evacuation zone could be assigned to specific public shelters. Although shelter assignments may serve to minimize clearance times in areas where shelter space is critical, in other areas the effects could be negligible.

(7) Vertical Evacuation and Refuge. Vertical evacuation is the preplanned relocation of occupants of vulnerable areas to the upper levels of specifically identified and assigned multi-story buildings. Vertical refuge is the similar relocation of those occupants because of inadequate time or opportunity for them to leave the area.

(1) General. The primary purpose of the transportation analysis is to calculate the clearance times needed to conduct a safe and timely evacuation for a range of hurricane threats. Other purposes are to define the evacuation roadway network and to evaluate traffic control measures/highway improvements for improved traffic flow.

(2) Evacuation Travel Patterns. During a hurricane evacuation, a large number of vehicles must be moved across a roadway network in a relatively short period of time. As pointed out by the behavioral analysis, the number of evacuating vehicles will vary as a function of the intensity of the hurricane, the number of tourists in the area, and certain behavioral response characteristics of the evacuees. Vehicles enter the road network at different times, depending on each evacuee's response to an evacuation order or advisory. Where vehicles leave the roadway network depends on both the planned destinations of evacuees and the availability of acceptable destinations such as public shelters, hotel/motel units, and friends or relatives in nonvulnerable locations.

(3) Analysis Input. Since all hurricane situations differ in some respects, it is necessary to set forth clear assumptions about storm characteristics and evacuee response before transportation modeling can begin. Changes in storm characteristics, particularly intensity, that affect the vulnerability of coastal residents can cause a wide variation in evacuation response. Since the circumstances under which future hurricane evacuations may be conducted vary widely, sensitivity analyses should be performed during the transportation modeling. Those variables having the greatest influence on clearance times should be identified and then varied to establish a logical range within which actual values should fall. Key input assumptions that affect the transportation analysis are grouped into five areas:

(b) Socioeconomic Data. Current population and housing unit data by subarea (census tract, enumeration district, or traffic analysis zone); mobile home and seasonal/tourist unit data as available and appropriate; vehicle ownership data; income information if available.

(c) Behavioral Analysis. An analysis of the probable behavioral response characteristics of the population focusing on expected percentages of participation by the population, destination types, rate of response, and vehicle usage.

(d) Sheltering Information. Public shelter and hotel/motel capacities and locations; local emergency management and American Red Cross operational policies affecting timing and/or capacity.

(e) Roadway Network Information. Number of travel lanes by direction per roadway segment, intersection characteristics and operations, bridge locations and operations, traffic count data, and evacuation traffic control assumptions.

(a) General. The transportation analysis is necessarily broad in scope, usually requiring complex computer modeling techniques. Although some states and large metropolitan areas have organizations with the capability of undertaking transportation studies within specific jurisdictions, a regional or multi-regional analysis can usually be conducted more effectively by a consulting firm with expertise in modeling procedures directly applicable to hurricane evacuation.

(b) Evacuation Scenario Development. Hypothetical hurricanes that have unlike characteristics but similar effects on the study area should be grouped into evacuation scenarios.

(c) Evacuation Zone Development. Data gathered by census tracts, enumeration districts, traffic analysis zones, or other data base units should be grouped by evacuation zone.

(d) Dwelling Unit Data by Evacuation Zone. Population, dwelling unit, vehicle ownership data, etc., collected by census tract, traffic analysis zone or other unit must be allocated to the evacuation zones.

(e) Evacuation Roadway Network Designation. Each jurisdiction's existing hurricane evacuation routes are evaluated. In choosing roadways for the hurricane evacuation network, care should be taken to designate only those roads that are not expected to flood from rainfall or storm surge while the evacuation is in progress. Ideally, other desirable characteristics are little or no adjacent tree coverage, substantial shoulder width and surface, and current designation as an evacuation route in an existing evacuation plan.

(f) Trip Generation. Population data gathered in the vulnerability analysis should be used in the trip generation calculations to produce the total evacuating population and vehicles that originate in each evacuation zone. For each zone, numbers of evacuating population and vehicles should be grouped by destination type (trip purpose). For hurricane evacuations, destination types are local public shelter, local friend's/relative's home (including churches, union halls, etc.), local hotel/motels, and out-of-county/out-of-study area.

(g) Trip Distribution. This step develops trip tables showing zone-to-zone and zone-to-county/jurisdiction exit point vehicle movements for each destination type and storm scenario. It involves judgements about which zones will fill available public shelter space and hotel/motel rooms in inland "dry" zones.

(h) Trip Assignment. This step assigns the trip interchanges for a particular scenario to the coded evacuation road network.

(i) Calculation of Clearance Times. Evacuating vehicles move at speeds limited by the relationship of traffic loadings on the various roadway segments to the ability of the segments to handle those loadings (roadway capacity). Based on the hourly capacity for each critical link, and the hourly volume desiring to use the link, queuing delay times and evacuation travel times can be calculated.

(5) Transportation Analysis Products. Although considerable amounts of information are produced in the transportation analysis, the following products are particularly important to hurricane evacuation preparedness and post-storm evacuation assessments.

(a) Evacuation Zone Map. All study area zones are delineated and surge-vulnerable zones are variously shaded to indicate levels of evacuation by scenario.

(b) Evacuation Road Network Map. These maps show the roadways included in the traffic modeling and the relation of the evacuation zones to the road network. They should clearly show the nodes and link names used in the modeling.

(c) Dwelling Unit Data. A listing of census/traffic analysis zone delineations and data with their relation to the evacuation zone system, and a listing by evacuation zone of the number of permanent units, mobile home units, seasonal units, etc., should be provided.

(d) Evacuating People and Vehicle Tables. These tables show the output of the trip generation task. The total number of evacuees and evacuating vehicles produced by every evacuation scenario and tourist occupancy level tested is available for each evacuation zone.

(e) Evacuation Road Network Link File. This file shows a link by link listing of assumed roadway characteristics including the number of lanes by direction; if appropriate, a generalized estimate of the link's service volume at a specified level should be given.

(f) Trip Tables by Storm Scenario. For each scenario, this output of the trip distribution task shows the zone-to-zone vehicle movements and the assumed number of vehicles from each zone exiting the county or other jurisdiction at certain points.

(g) Zone-to-Zone Paths. Depending on the modeling approach, tables should be presented which show the road segments used to move traffic from one zone to another.

(h) Evacuating Vehicles by Roadway Segment. For each storm scenario, the total number of evacuating vehicles assumed to use each roadway segment should be reported.

(i) Critical Roadway Segments and Intersections. Volume to capacity ratios are calculated for heavily traveled roadway segments. Segments with the highest ratios are identified as critical links. Critical links and intersections control the flow of evacuating traffic during a hurricane evacuation and are key areas for special traffic control.

(j) Clearance Time Tables. The most important products of the transportation analysis are the clearance times, which vary depending upon storm scenario; behavioral response; and, if appropriate, tourist occupancy level. The behavioral analysis determines when the evacuees will leave relative to a given evacuation order or advisory (response rate) and the rate at which they will leave. Clearance time is normally estimated for each county. It begins when the first evacuating vehicle enters the roadway network, prior to an evacuation order or advisory, ends when the last vehicle reaches an assumed point of safety, and includes the time spent traveling along the roadway network and waiting due to traffic congestion (queuing delay time). It does not relate to any one vehicle. In estimating clearance times, it is of utmost importance to provide adequate time to safely evacuate the vulnerable population, but the consequences of a premature evacuation order or advisory must also be recognized.

(k) Traffic Control Measures. The movement of evacuating vehicles during a hurricane evacuation requires extensive traffic control efforts to make maximum use of roadway capacity and to expedite safe escape from hurricane hazards. The transportation analysis should reveal critical roadway segments and intersections and recommend specific traffic control measures and/or roadway modifications to help alleviate the anticipated problems in these areas. The development of traffic control techniques for critical evacuation routes should always involve state and local police, emergency management, and fire department officials and, if appropriate, the U.S. Coast Guard for bridges.

Several approaches developed by the USACE, FEMA, and the private sector are available to state and local officials to aid in hurricane evacuation decision making. These include the Decision Arc Method and the HURREVAC, GDS, HURRTRAK, and other computer programs. The Decision Arc Method, HURREVAC, and GDS are related techniques that determine the latest time at which an impending evacuation order or advisory should be given by integrating information extracted from the NHC Tropical Cyclone Forecast with data developed in the hurricane evacuation study. They also take into account strike probabilities produced by the NHC. Since several factors must be weighed in evacuation decision making, none of these approaches is designed to be a decision-making mechanism.

The Decision Arc Method was developed by the USACE to deal with inherent problems in relating hurricane evacuation to "eye landfall". It departs from the "time-to-landfall" approach by translating clearance times into distances on a hurricane tracking chart, and prelandfall hazards times into distances on a two-dimensional hurricane graphic. This combination visually depicts a threatening hurricane situation. HURREVAC, developed by FEMA, and some computer programs available commercially function in a fashion similar to the Decision Arcs but use a system based on local time rather than distances. Since these programs depend on an operating computer, they should always be backed up by the manual Decision Arc Method.

(1) General. When a hurricane approaches a coastline at an acute angle, as is the usual case along the Atlantic seaboard, a small error in the forecast track can rather drastically change the point of landfall, significantly increasing or decreasing the distance and time to landfall. The forward motion of hurricanes can also accelerate and decelerate, causing the time of landfall to be even more unpredictable. Rather than base hurricane evacuation decision making and mobilization on forecast time and point of landfall, methods are available to help compensate for forecast errors by relating evacuation operations to actual hurricane position and movement.

The Decision Arc Method employs two separate but related components which, when used together, present a graphic depiction of the hurricane situation as it relates to each jurisdiction. A specialized hurricane tracking chart, the Decision Arc Map, is paired with a two-dimensional hurricane graphic, the STORM, to describe the approaching hurricane and its relation to the area considering evacuation.

(2) Decision Arc Map and STORM. Decision Arcs are nothing more than clearance times converted to distance by accounting for the forward speed of the hurricane. This method requires the development of special hurricane tracking charts with a series of concentric arcs usually centered on the southernmost boundary of each county. The largest of these concentric arcs should have a radius at least as large as the quotient of the longest clearance time, measured in hours, multiplied by the greatest expected hurricane forward speed, expressed in knots. The resulting radius would be measured in nautical miles.

The Special Tool for Observing Range and Motion (STORM) is used as a two-dimensional depiction of an approaching hurricane. It is a transparent disk with concentric circles spaced at equal nautical mile intervals, their center representing the hurricane eye. These circles form a scale used to note the radii of tropical storm winds reported by the NHC in the Tropical Cyclone Forecast.

(3) Method of Application. To translate a clearance time into nautical miles (Decision Arc distance) for use with the Decision Arc Map, simply multiply the clearance time by the forward speed of the hurricane in knots. This calculation yields the distance in nautical miles that the hurricane will move while the evacuation is underway. For convenience, a Decision Arc Table can be developed for each community to convert an array of clearance times and forward speeds to respective Decision Arcs. To use the Decision Arc method, officials plotting an approaching hurricane on the Decision Arc Map should make an evacuation decision prior to the time when the selected radius on the STORM crosses the appropriate Decision Arc (the Decision Point). As the Decision Point nears, factors such as hurricane category, NWS probabilities, forward speed/acceleration, and possible forecast errors must be considered. Once the selected STORM radius crosses the Decision Arc, there is no longer sufficient time to safely evacuate the vulnerable population without employing extraordinary measures to hasten their departure.

HURREVAC includes many of the features of the Decision Arc Method. It uses the radii of tropical storm winds and hurricane forward speed reported in the NHC Tropical Cyclone Forecast to determine the prelandfall hazards time for an approaching hurricane. The program then assumes a worst-case scenario by adjusting the forecast track to aim the hurricane directly toward the jurisdiction in question. Therefore, as with the Decision Arc Method, evacuation timing is not related to a forecast point of landfall or time of landfall. By integrating the calculated prelandfall hazards time with clearance times from the technical data report already contained in the program, HURREVAC will calculate the local time when an evacuation decision must be made, the time when tropical storm winds could arrive in the community, and the time when the hurricane eye could make landfall. The probability values from the NHC Tropical Cyclone Forecast are incorporated into another feature of the program. Using those values, along with the hurricane category, forward speed, and track, the program will select from an array of evacuation scenarios the evacuation decision most often made, historically, under similar circumstances.

The HURREVAC program also includes graphic displays of the evacuation zone maps for the study area; past, present, and forecast hurricane locations; and the tropical storm wind field. A separate display of the inland wind field information mentioned previously [see Hazards Analysis, Wind Hazards] is available for the entire Gulf of Mexico coastline and the Atlantic coast as far north as North Carolina.

The technical data report gives a detailed description of how the study was performed and the study results. It should contain written descriptions of the conduct and results of each study task and all maps, diagrams, and tables needed to support those descriptions..

The USACE should provide technical assistance to state and local emergency management officials in preparing or revising evacuation plans. Assistance should be in the form of interpreting information developed in the evacuation study and training in the use of that information. Training should include a tabletop exercise, preferably involving FEMA and the NWS, using the Decision Arc Method and any other available decision-making aids.

The Study Manager should work with state and local emergency management officials to develop and disseminate publicity designed to educate potential evacuees. Public information materials can take many forms: brochures for distribution in the study area, tabloids printed by local newspapers, information printed into telephone books, taped audio and visual presentations, slide presentations, wall maps, and others.

A regional hurricane evacuation exercise sufficient in scope to test all major elements of the hurricane evacuation plans should be conducted. The participants should include state, regional, and local agencies that have hurricane emergency preparedness responsibilities. The scope could range from only tabletop communications to full activation of field personnel and emergency operations centers. Regardless of the scale, the goal of the exercise should be to test the effectiveness of each plan in affording the public a safe, efficient, and effective evacuation from a hurricane threat.

The exercise should test the ability of emergency management officials to identify the appropriate evacuation scenario as it develops, including those of neighboring communities. Official's responses should be tested in the areas of evacuation decision making, communications, public warnings, manpower/equipment deployment, resource allocation, timing of evacuation order or advisory, shelter activation, emergency transportation, and traffic control. Communications and emergency power systems should be fully tested, long-term if possible. Monitors should be stationed at each emergency operations center and, if appropriate, in the field to evaluate response activity.

A post-exercise review should be conducted to evaluate the effectiveness of each plan. Officials who participated in the exercise should also contribute to the review. Monitors should be asked to critique the activity to which they were assigned. A critique report should be published at the state level that documents the exercise methodology, identifies problem areas, and recommends improvements. Areas where future preparedness training would be beneficial should also be identified.

There are no rigid boundaries between hurricane evacuation study maintenance, updates and restudies. Rather, there is a gradual increase in scope and/or complexity as the effort moves from maintenance to update to complete restudy. The following paragraphs address typical features and activities which might be expected to fall within these categories.`

As part of a state or local jurisdiction's yearly maintenance of hurricane evacuation plans and procedures, they should routinely evaluate certain data treated or developed by the hurricane evacuation study. Information about changes in population, numbers of seasonal housing units and/or mobile homes; availability of more detailed topography; changes in shelter inventories; and changes to access/egress routes (new bridges, roads, ferries) is often most readily accessible to a local jurisdiction. Ongoing maintenance of the data base should result in much faster and more efficient updates and/or restudies.

This effort is triggered by changes in characteristics of the study area or availability of advances in study procedures or products that have the potential to improve the capabilities of states or local jurisdictions. No significant changes in expected surge limits are anticipated from the base study. Minor changes to behavioral assumptions may be made but no new public surveys are performed. The transportation analysis is revised to reflect significant population increases, roadway improvements on key evacuation corridors, and public shelter changes. Additional evacuation scenarios may be incorporated based on new traffic control assumptions. Study updates will include evaluating alternatives that may lower long evacuation clearance times. New base mapping may be incorporated and digital/GIS technology introduced where previously unavailable. Decision making tools are revised with new clearance times and shelter list changes. Tables in the current technical data report are revised as necessary.

This effort is triggered by major changes in characteristics of the study area or availability of advances in study procedures or products. Examples would include: large increases in vulnerable population; a direct hit by a hurricane resulting in demographic changes or expected public response; changes to the SLOSH model that result in significant differences in expected surge limits. Some or all study components would need to be revisited. A major revision of the technical data report is accomplished and updated tools for decision making are provided.

This analysis meshes together evacuation data from several different hurricane evacuation studies. Impacts of one region's evacuees on another region are considered. Major public transportation providers are identified for hazards and vulnerability analysis and for evacuation clearance time considerations. Forums are provided for different states and regions to coordinate on responses and information flow that will need to take place for future storm events.

As the national hurricane evacuation experience base increases, there will be continual advances in evacuation planning concepts and operations procedures. Changes in the "state of the art" of hurricane evacuation studies will reflect these advances. It can be expected that at certain times individual or multiple study areas will be able to benefit from additions or modifications to their study products as indicated by experience in other jurisdictions. Similarly, factors such as advances in surge modeling, evacuation decision software, mapping, shelter selection criteria, etc. can be expected to eventually reach a point where an update or a restudy is indicated.

In some jurisdictions, the size of the vulnerable population, lack of evacuation routes, or other factors have produced calculated clearance times of 24 hours or more. Clearance times of this length can require jurisdictions to make evacuation decisions when hurricane strike probabilities are rather low. For these areas, any changes in clearance times can be critical. All other factors being equal, study areas with longer clearance times will have higher priority to receive Federal funding for updates than those with more manageable times. In considering requests for funding of hurricane evacuation study updates or restudies, FEMA Headquarters and the HQUSACE will place significant emphasis on areas with clearance times of about 24 hours, or if there is reason to believe that the changes will lead to such clearance times.