Planning for the Evacuation of New Orleans

Transcription

1 Planning for the Evacuation of New Orleans THIS FEATURE BRINGS TO LIGHT THE EXTENT TO WHICH NEW ORLEANS IS THREATENED BY HURRICANES AND DETAILS THE PLANS TO EVACUATE THE CITY WHEN THREATENED. IT SHOWS THAT WHILE SOME OF THE TRANSPORTATION PROBLEMS THAT CONFRONT THE CITY DURING EVACUATIONS ARE UNIQUE, MOST ARE ALSO SIMILAR TO THOSE FACED BY OTHER COASTAL CITIES IN THE UNITED STATES. BY BRIAN WOLSHON NATURAL DISASTER PLANNING for cities in the United States typically falls under the jurisdiction of emergency planning and law-enforcement agencies. Historically, engineers have played critical supporting roles to these agencies by providing expertise in, among others, flood modeling and mapping and building survivability. One area where engineers have had relatively little input to the disaster planning and preparedness effort in the past has been in the area of transportation planning and evacuation traffic management. Evacuations have historically been managed at a local level by emergencymanagement agencies. Relatively little attention has been given to region-wide evacuations that require the maximized and/or coordinated use of the transportation infrastructure. Likewise, transportation professionals, in both engineering and planning, rarely incorporated the needs of evacuation in their day-to-day traffic planning, design and analysis activities. The result of this lack of involvement was evident in several recent evacuations where the transportation infrastructure was not used to its full potential when the need arose. Emergency-management officials in the New Orleans, LA, USA, metropolitan area are now working to overcome this problem by teaming with the Louisiana Department of Transportation and Development (DOTD) to develop a comprehensive regional plan to evacuate the city in the event of a hurricane. This feature describes the plan to evacuate the city of New Orleans when under threat of a major hurricane. It also highlights the problems that are particular to evacuating the city and the creative ways that disaster and transportation planning agencies are working to solve them. This feature also presents, from a transportation perspective, several other critical issues that affect the movement of people during evacuations. BACKGROUND The New Orleans metropolitan area is home to approximately 1.4 million inhabitants. It is also completely surrounded by water, although merely being surrounded by water is only part of the problem. The primary dilemma faced by New Orleans is that it is situated on land that is predominantly below sea level. Ground surface elevations in the city average about 2 feet (ft.) below sea level, with some parts of the city, like those near Lake Pontchartrain, as much as 10 ft. below sea level. By contrast, the surface elevation of the Mississippi River averages about 1 to 2 ft. above sea level. Thus, during average conditions, the water that surrounds the city is often as much as 10 to 15 ft. above street level. The city has grown and prospered, free from the fear of flooding thanks in large measure to an elaborate system of levees, drainage canals and pumping systems. The relative safety that the levees provide and the low level of major hurricane activity in southeastern Louisiana over the past 35 years have combined to foster attitudes of complacency to the significant threat that exists from tropical storm flooding in this region. Recently, however, the complacent attitudes of prior decades have begun to change. In 1992, Hurricane Andrew missed New Orleans, making landfall about 150 miles to the west. In 1998, Hurricane Georges was forecast to make landfall at the mouth of the Mississippi River and make a direct hit on downtown New Orleans at Category 3 strength. (See Table 1.) A full evacuation was ordered for the city and surrounding parishes. Fortunately for the city this storm also missed the city, turning east just hours prior to landfall, although the storm did go on to cause significant damage to the Mississippi and Alabama gulf coast cities of Gulfport, Biloxi and Mobile. In the aftermath of Georges, the agencies responsible for emergency manage- 44 ITE JOURNAL / FEBRUARY 2002

2 Table 1. Hurricane categories. Hurricanes are rated in intensity on the Saffir-Simpson Hurricane Scale. This scale (shown below) rates hurricanes by their wind speed, barometric pressure, storm surge height and damage potential. Category Wind Speed Barometric Pressure Storm Surge Damage Potential miles per hour (mph) inches (in.) or more feet (ft.) (Weak) knots (kts) millibar (mb) or more m mph in ft. (Moderate) kts mb m mph in ft. (Strong) kts mb m mph in ft. (Very strong) kts mb m 5 > 155 mph < in. < 18.0 ft. (Devastating) > 135 kts < mb < 5.5 m Minimal damage to vegetation Moderate damage to houses Extensive damage to small buildings Extreme structural damage Catastrophic building failures possible ment in the New Orleans area began to reassess their plan to evacuate the population of metropolitan New Orleans. This need was further reinforced in the aftermath of Hurricane Floyd in In September of that year, Floyd threatened the Atlantic coast from Florida to South Carolina before finally making landfall in North Carolina. The size and strength of Floyd, along with the intense media coverage it received, precipitated the largest evacuation in U.S. history and resulted in virtual gridlock on freeway evacuation routes in these states. Most coastal cities have the ability to move people away from the threats of hurricanes (flooding and wind) by moving them into sound structures at elevations above storm-surge flood levels. New Orleans does not have that luxury; people must evacuate. With much of the city below sea level, storm models have shown that even a moderately strong hurricane would inundate the levees, submerging portions of the city under 10 to 20 ft. of water. The models also showed that the levees, built to protect the city from flooding, would actually work in reverse during a hurricane by holding waters within their banks after the surge recedes. As a result, a total evacuation of all areas within the levees is required. To accelerate the flow of evacuees out of the city, local and state emergency-planning and transportation officials in Louisiana have developed an evacuation plan that includes the reversal of freeway routes into the city. Under this plan, traffic flow on some or all of the inbound lanes of the freeways into the city will be reversed to flow in the outbound direction. These contraflow evacuations were used during Floyd in both Georgia and South Carolina with mixed success. The question that has not been answered is: Will such a plan work for New Orleans? The concept has been rehearsed by various emergencymanagement, law-enforcement and transportation agencies. However, it has never been (nor can it realistically ever be) operationally tested. As such, no one knows how well, or even if, it will work. THE NEW ORLEANS EVACUATION PLAN In response to the need for a full evacuation, emergency-preparedness officials, in conjunction with local and state transportation and law-enforcement agencies, have developed a regional plan to evacuate the New Orleans metropolitan area in the event of a major hurricane. The New Orleans evacuation plan recognizes that while a total evacuation of the city may be required, an evacuation of only part of the population is practically possible. Of the 1.4 million inhabitants in the high-threat areas, it is assumed only approximately 60 percent of the population or about 850,000 people will want, or be able, to leave the city. The reasons for this are numerous. Although the primary reasons are a lack of access to transportation (it is estimated that about 200,000 to 300,000 people do not have access to reliable personal transportation), an unwillingness to leave homes and property (estimated to be at least 100,000 people) and a lack of outbound roadway capacity. To increase the limited outbound roadway capacity, New Orleans officials are planning to use contraflow operation on its interstate freeways. Contraflow (also referred to as one-way-out evacuation) involves the use of one or more inbound travel lanes for the movement of traffic in the outbound direction. Georgia and South Carolina were the first states to implement interstate contraflow for a mass evacuation during Hurricane Floyd in Now, every coastal state from Virginia to Texas has or is in the process of developing plans to use interstate lane reversals during evacuations. 1 While the concept is relatively simple, there are many inherent difficulties associated with reversing flow on a freeway, particularly during an evacuation. For a description of the mechanics of contraflow evacuations as well as the costs and benefits associated with its use, interested readers are urged to refer to other recent reports on this subject. 2,3 ITE JOURNAL / FEBRUARY

3 Limitations of the New Orleans Highway Network for Evacuation The primary hindrance to the evacuation of New Orleans is the limited number of routes leading out of the city. The general orientation of highways in metropolitan New Orleans is east-west. The area is served by a single interstate freeway, interstate 10, that traverses the entire metropolitan area. Three U.S. highways, 11, 90 and 61, parallel I-10 on the east and west sides of the city. Louisiana state highways 44 and 48 also parallel I-10 to the west. The Lake Pontchartrain Causeway is the sole northbound route out of town, spanning approximately 23 miles over the lake. Interstate 55 is also a northbound route, although it joins I-10 approximately 20 miles to the west of the city. An additional constraint, from the perspective of an evacuation, is that all of these routes cross over long sections of water. I- 10 spans the south shore of Lake Pontchartrain for about 12 miles and the eastern shoreline for seven miles. The profile of the at-grade, noninterstate routes are nearly flat and only 1 or 2 ft. above water level. As a result, sections of U.S. 90, U.S. 11 and U.S. 61 are all prone to flooding, even during moderate to heavy thunderstorms. The Lake Pontchartrain Causeway, while much less susceptible to flooding, must also be closed to traffic when winds exceed 45 mph. These factors, coupled with the surge and flood potential brought about by approaching hurricanes, severely limit the evacuation routes out of the city. Evacuation Routing and Contraflow Plan The plan to evacuate the city involves all available routes out of New Orleans, while maximizing the utilization of I-10. In contrast with other states, the freeway contraflow aspect of the plan is only used a relatively short distance (approximately 20 miles). However, what the New Orleans plan lacks in contraflow length, it makes up for in efficiency. U.S. 90 and U.S. 11 will also be used as long as they are safely passable. It is expected that the winds and high water preceding the storm will necessitate the closure of these routes first, then the causeway, then the elevated sections of I-10. The decision to close these routes will be made by a state police commander, in conjunction with officials from the Figure 1. New Orleans primary evacuation routes. (Map Source: Rand-McNally, 2000) Figure 2. Louisiana State Police traffic control plan, the I-10/Loyola Drive interchange. DOTD and the Office of Emergency Preparedness. The state police will also preposition wreckers at strategic locations to remove disabled vehicles on these routes. Evacuation traveler information will be available through two local radio stations through the Emergency Broadcast System (EBS). 4 Additional traveler information will be provided by the DOTD highway advisory radio network. Under the New Orleans plan, diagrammed in Figure 1, traffic evacuating the western metropolitan area will be divided into two separate streams. Louisiana State Police personnel will route traffic in the left two lanes of westbound (outbound) I-10 into the eastbound (inbound) lanes prior to the I-10/I-310 interchange as diagrammed in Figure 2, using the two-lane, paved median crossover shown in Figure 3. Lightweight water-filled barriers prohibit median crossings at this location during nonevacuation periods. Prior to an evacuation these will be drained and removed by DOTD personnel. Both traffic streams will parallel one another over the Bonnet Carré Spillway Bridge section of I-10 over the south shore 46 ITE JOURNAL / FEBRUARY 2002

4 Figure 3. Westbound I-10 median crossover at Loyola Drive. Figure 4. Louisiana State Police traffic control plan, the I-10/I-55 interchange. Figure 5. I-10 contraflow termination median crossover. of Lake Pontchartrain. Some 20 miles later, at the I-10/I-55 interchange, all traffic moving in the normal westbound lanes will be forced to head north on I-55 as shown in the Louisiana State Police schematic diagram of Figure 4. After the interchange, the contraflow traffic in the eastbound lanes will cross back into the westbound lanes of I-10 using the median crossover shown in Figure 5. To reduce the demand on the outbound lanes of I-10, traffic evacuating north from the west bank side of the Mississippi River on northbound I-310 will be routed to northbound U.S. 61, a four-lane divided highway. When U.S. 61 becomes impassable from the rising waters of Lake Pontchartrain, this traffic will be diverted to LA 48 parallel to and east of the Mississippi River. Although westbound I-10 is completely over water out of New Orleans, this fact should actually help to facilitate the evacuation. One of the complicating aspects of contraflow evacuation is the need to prevent evacuees in the contraflow lanes from exiting the freeway and preventing inbound vehicles from entering the roadway in the wrong direction. Since there are no exit/entrance ramps between the beginning and ending of the contraflow segment, this will not be an issue on I-10. This will also minimize the amount of traffic enforcement personnel required to implement and maintain the plan and should reduce motorist confusion. More significantly, the layout of the westbound New Orleans freeway network will not necessitate a merge point at its termination. Since all evacuees in the normal westbound lanes will be forced to proceed north on I-55, the contraflow traffic will cross back into the empty westbound lanes after the I-10/I-55 interchange. Merging of separate traffic streams at the end of contraflow sections is a major concern of evacuation traffic planners because the merging of four lanes of evacuation traffic into two will only move the location of traffic congestion, rather than eliminating it. Other states have dealt with this issue in different ways, including the use of long segments (greater than 100 miles) that draw off traffic over its length. 1 CRITICAL ISSUES When planning for an evacuation, the goals and procedures for evacuation are often quite different from those used to address routine traffic-planning and congestion-management issues. An evacuation is an extreme response to an extreme threat where the potential for mass loss of life exists. Under such conditions, many of the standard principles and practices that govern traffic flow and ITE JOURNAL / FEBRUARY

5 control may be ignored in favor of potentially higher risk practices that can increase roadway capacity and reduce clearance times. These may include the use of reverse laning, using shoulders as an additional lane, routing traffic through partially completed construction zones and deactivating traffic signals. The traffic mix during an evacuation can also be quite different from normal conditions. Drivers are under the added stress of potential loss of life and property. Evacuating vehicles are often filled with children, the elderly, pets and personal belongings. Evacuees also often pull heavy trailers with their vehicles. In addition, evacuees have a tendency to move all driveable vehicles from the evacuation zone, including recreational, off-road, vintage and under-repair vehicles, despite the fact that some them may be marginally roadworthy. These factors combine to not only increase demand, but also decrease roadway capacity. Evacuations also increase the demand for roadside comfort facilities, disabled vehicle clearing crews and repair and fueling stations. In addition to operational issues of the evacuation, there are also strategic and administrative concerns, several of which are still being addressed as part of the New Orleans plan. Some of these are being dealt with through engineering efforts. However, some are also related to the new efforts to develop a cooperative approach to evacuation and an environment in which business as usual attitudes need to be overcome for creative solutions to be generated. Several of these issues are presented below in New Orleans-specific terms. However, they are applicable to any states that need to employ emergency evacuations in times of crisis. Interstate Movement of Evacuees One of the controversial aspects of contraflow is its use across state lines. Presently, no states have agreements to operate contraflow freeway lanes between states. During Floyd, tremendous numbers of evacuees moved up the East Coast from Florida to Georgia and into South Carolina without contraflow, causing near-gridlock conditions. Similar conditions were encountered on I-10 as people fled New Orleans. To lessen the likelihood of these conditions in the future, discussions between Mississippi and Louisiana officials are underway to establish an interstate contraflow agreement. As described earlier, the plan to evacuate New Orleans to the west is well established. However, the plans to evacuate the east side of the metropolitan area are still under development. The geography of the region dictates that New Orleans evacuees will have little choice but to head into Mississippi. Unlike the west side of the city, there are limited routing options once I-10 returns to grade at the interchange of I- 12/I-59. Directing evacuees east or west on I-10 could potentially send them directly into the path of a hurricane. This leaves northbound I-59 as the only viable option. The plan favored by Louisiana officials would mirror operations on the west side of town, using the elevated section of I-10 over the eastern edge of Lake Pontchartrain in contraflow fashion (shown in Figure 1). The suggested plan is to continue the I-10 contraflow operation through the I-12/I-59 interchange and into Mississippi. Unfortunately, Mississippi highway officials have been somewhat reluctant to continue I-59 contraflow into their state. The Mississippi Department of Transportation (MDOT) objections to I-59 contraflow into Mississippi are primarily safety related. MDOT officials fear that a lane reversal could hamper efforts to reach disabled vehicles on I-59 and affected southern communities. They are also concerned that the need to control traffic along the route could put a strain on available lawenforcement personnel. There are also concerns that the movement of tremendous numbers of people from New Orleans (potentially numbering in the hundreds of thousands) could hinder the evacuation of Mississippi coastal residents and possibly overtax the sheltering resources of the state. Nonetheless, Mississippi officials recognize the dangers that face the citizens of New Orleans, and the dilemmas faced by their counterparts in Louisiana, and are currently working to resolve this issue. Roadway Safety The benefits of contraflow evacuation on freeways come with an increased level of risk. Freeways are designed for travel in one direction. Guidance features like signs and pavement markings may not be visible to drivers traveling in the opposite direction. Likewise, roadway safety features such as crash attenuators, guardrail transitions and breakaway support posts are not designed to provide protection from the reverse direction. There is also the risk of vehicles entering the reverse flow lanes from the wrong direction. When these factors are combined with the stress of evacuation and the confusion that exists for drivers unfamiliar with contraflow, such operation can move from a level of inconvenience to one of danger. Despite these risks it is also recognized that time is of the essence during evacuations and any delay can potentially result in loss of life. So, while careful attention must always be paid to safety, these risks associated with nonstandard practices must be carefully weighed against the need to increase capacity. Louisiana, like several other states using contraflow, plans to use state police personnel and in some cases National Guard troops to maintain safe and orderly evacuations and minimize the potential for accidents. Entry points into contraflow will be barricaded and guarded. On-route traffic enforcement will also be used to maintain lower travel speeds at safe levels, if required. The North Carolina Department of Transportation is also investigating the use of two-way guidance and dynamic message signs so that they are visible to drivers during contraflow operations and reconstructing some guardrail end terminals and transitions to make them crashworthy in either flow direction. Construction Zones Another issue being examined, as part of the New Orleans evacuation plan, is the occurrence of construction zones on evacuation routes. In 1998, during the Georges evacuation, sections of I-10 from New Orleans to Baton Rouge and I-12 from Hammond to Baton Rouge were under construction, leaving a single lane of traffic open in the construction zones. Fortunately, the contractors on both projects were able to open two lanes in the outbound direction of travel soon after the evacuation order was given. While Louisiana DOTD officials were able to avoid problems during Hurricane 48 ITE JOURNAL / FEBRUARY 2002

6 Georges, they are looking for better ways to maintain full capacity in evacuationroute construction zones in the future. Suggestions have included limiting the construction season, distance, performance time and/or phase sequencing of projects on evacuation routes. However, no specific policy with regard to this issue has been set. Recent experiences by the Florida Department of Transportation showed that when such restrictions are written into construction contracts, the cost of reconstruction projects increased significantly. As such, they are being carefully evaluated at this time. Unpredictability of Hurricane Forecasting and the Time Required to Evacuate the City Another significant issue is the limited ability to forecast hurricanes and its effect on evacuation travel demand. The decisions on what area to evacuate, when to start it, when to end it and where to shelter evacuees are all based on the track and severity of the storm. Unfortunately, the task of forecasting the movement and development of hurricanes can be a tenuous one. Current storm-track forecasting systems are able to predict strike location within about 100 miles, 24 hours before the storm makes landfall. This accuracy rate, while an improvement over past years, is still not accurate enough or early enough to give emergency managers the advanced warning time they need to evacuate a city the size of New Orleans. It also makes it difficult to make potentially costly evacuation decisions, and more importantly, to get people to take mandatory evacuations seriously. It has been estimated that a full evacuation of New Orleans will take 72 hours. In 1998, the weather in New Orleans was sunny and pleasant 72 hours prior to the landfall of Hurricane Georges. These conditions, coupled with the wide strike probability band shown on weather forecasts, did not raise an alert for most people to evacuate the area. As a result, the major thrust of the evacuation did not start until it became apparent the storm was tracking directly toward the center of New Orleans, some 24 to 36 hours before landfall. Had Georges maintained the strength and track forecast, casualties could have exceeded 50,000. One way to address this issue is to initiate a mandatory evacuation as early as possible. However, this raises a multifaceted problem. First, the cost of evacuations, in terms of personnel and material resources and lost productivity is enormous. Estimates of the cost of an evacuation range from about $200,000 to $1,000,000 per mile of coastline, depending on the location. At these rates, an unwarranted evacuation order could result in the loss of tens or hundreds of millions of dollars. Premature evacuation orders also have the potential to send evacuees into the path of a storm that moves in a different direction. Another problem is the Cry Wolf scenario. If mass numbers of people are required to evacuate for a storm that never strikes, it is likely that they will be much less eager to evacuate early the next time. Emergency-management officials are well aware of these issues and are cautious to balance the accuracy of current predictions with the costs of issuing incorrect evacuation orders. However, when in doubt, they will always look to err on the side of caution. CONCLUSION Census figures show that the population of the coastal areas of the southeastern and gulf-coast states of the United States continues to grow rapidly. As shown during Hurricane Floyd in 1999 and during Hurricane Georges in 1998, many of these areas may not be suitably prepared to deal with the need for mass evacuations under threat of hurricanes. To meet the need for faster and more efficient evacuations, disaster-planning agencies are presently seeking to more actively involve transportation professionals in the evacuation planning and preparedness process to develop strategies to effectively use and manage the transportation infrastructure when the need arises. However, the general level of involvement and awareness in the transportation community remains limited with regard to these issues. Despite the fact that evacuations are rare events, transportation officials in threatened states need to consider them in the planning of future highways, control plans and intelligent transportation systems (ITS). Research must also continue to identify better ways to address issues of safety, efficiency, information exchange and poststorm re-entry during evacuations. It has been suggested that the Institute for Transportation Engineers can also play a significant role by being the catalyst that brings together the collective expertise of transportation professionals in the field of evacuation and major-event traffic management. ACKNOWLEDGMENTS The author would like to acknowledge the technical assistance and information provided by Dr. Marc Levitan and Dr. Joe Suhayda of the Lousiana State University (LSU) Department of Civil and Environmental Engineering and LSU Hurricane Center and Sergeant Chris Bodet of the Louisiana State Police. References 1. Federal Highway Administration. Contraflow Operations on Interstates and Other Evacuation Routes. Summary from Session A of the FHWA Transportation Operations During Major Evacuations: Hurricane Workshop. Atlanta, GA, USA, June Wolshon, B. One-Way-Out: Contraflow Freeway Operation for Hurricane Evacuation. Natural Hazards Review. Vol. 2, Issue 3 (Aug. 2001): Federal Emergency Management Agency. Southeast United States Hurricane Evacuation Traffic Study. Washington, DC, USA, Louisiana State Police, Troop B. New Orleans Emergency Evacuation Plan. Kenner, LA, USA, June BRIAN WOLSHON, P.E., PTOE, is an Assistant Professor in the Department of Civil and Environmental Engineering at LSU. He received his B.S. from Wayne State University and M.S. and Ph.D. from Michigan State University. His professional interests are highway design/safety, ITS and traffic flow, particularly for hurricane evacuation. Wolshon is a Member of ITE. ITE JOURNAL / FEBRUARY