When a disaster strikes, whether natural or man-made, emergency evacuations are likely to be an important part of the response, and transportation authorities must be ready to facilitate the flow of people. Evacuations for any event can be difficult to plan. These can be large-scale undertakings that may involve thousands, even millions, of people trying to get out of one area in a short time frame. As numerous experts point out, transportation systems are not designed for evacuations, they’re designed for normal traffic flow on a given day. Thus, systems must be adapted when there is an evacuation. Complicating the planning is the fact that inhabitants often delay departure until the last possible minute, so traffic and roads become congested even more.

The key is planning for contingencies, whether that involves alerting the public to the best routes out, rerouting traffic on highways, or providing transportation for people without cars who live in the path of the hurricane, chemical spill, or other impending disaster. Ahead are lessons learned from past evacuations (most often related to hurricanes) and a look at how researchers are trying to use what they learn to lay the groundwork for improved evacuations in the future.

Decision Factors

Before people get on the road, they have to decide to evacuate. Researchers have looked at the factors that influence that decision, especially where it relates to warnings of an approaching hurricane. There are a few main issues that people will consider, says Jay Baker, associate professor in the Department of Geography at Florida State University and president of Hazards Management Group. Housing is one. People will consider whether their house is a safe place to ride out the storm. People who live in mobile homes are much more likely to evacuate than others for that reason, Baker says.

The overall risk of the area comes into play as well; people do evacuate from the more risky areas at a higher rate than elsewhere (though, as discussed later in this article, they sometimes misjudge how vulnerable they are). Also, people are much more likely to evacuate when they’ve been specifically told to do so.

Evacuation Orders

Transportation and behavioral researchers have been studying how the public responds to evacuation orders in an attempt to figure out how to make them more effective.

The first question is whether it helps to make them mandatory. Researchers note that while some municipalities have the authority to make evacuations mandatory, many don’t have the resources to enforce such orders if people ignore them. However, an even bigger factor is that significant numbers of people don’t know they are supposed to evacuate in the first place, says Baker, who notes that it’s not uncommon for as many as a third of the people in the evacuation area to be unaware that an evacuation order has been issued. 

The best way to ensure that everyone knows about an evacuation in their area, says Baker, is to go door to door and tell people about it. But that’s not practical for all areas, and it takes a lot of personnel. “The second most effective way, probably, is to drive through neighborhoods with loud speakers. But you have to do it a number of times. And some people still aren’t going to hear it. Their windows are closed, and they’ve got the television on and things like that,” he says. And while social media may reach some people, his research has shown that most people still receive the bulk of their evacuation information from television.

Social media…for hurricane information during a threat is still way, way behind everything else. And it’s hard to convince the emergency management agencies of that. They’re convinced that people rely on social media for hurricane information during a threat a lot more than we find is the case,” Baker says.

Additionally, people often don’t know when the evacuation orders refer to their location, because they don’t know which evacuation zone they are in. In an effort to tackle that problem, Charlotte County, Florida, has added colored bands to neighborhood stop signs in reflective colored tape to indicate storm surge risk. The stop signs near peoples’ homes correspond to their storm surge risk and when they hear, say, “red zone evacuate,” they’ll know whether it’s them or not. “So you don’t have to be able to read a map, and you don’t have to call or go to a Web site to type in an address, which they use in a lot of places,” says Baker. “No one has to knock on your door.”

People also respond differently depending on who issues the order. They are more likely to respond to an evacuation order if it’s issued by a community leader, such as the mayor. Additionally, Baker says that when the message is phrased in a way that makes it appear that the residents don’t have a choice, they’re more likely to leave. An example would be saying “this area is being evacuated,” rather than “authorities recommend that you evacuate.”

Another question is whether people will suffer evacuation fatigue if they live where hurricanes are common. Some are afraid about the “cry wolf” syndrome, meaning they worry that if people obey orders to evacuate and then the hurricane doesn’t hit as hard as had been expected, they’ll be discouraged from evacuating in future events. But Baker says that doesn’t seem to happen. He looked specifically at the case of Panama City, Florida, in 1985. There were three large-scale evacuations in a short amount of time; each time the storm ended up missing the area, and nearly the same percentage of people evacuated for each storm. 

Of the people who do receive the evacuation orders and still don’t leave, there are many factors that come into play, from not having anywhere to go to not having transportation. Social pressure also comes into play; people are more likely to leave or stay depending on what their neighbors and friends are doing.

Another issue may be pets, but many evacuation centers and shelters are now pet-friendly. However, Baker’s studies have found that much more than those sorts of considerations, people don’t leave because they simply think they’ll be safe. Unfortunately, their perceptions are not always accurate. But in addition to those who think they are safe when they are not, many people whose homes are not vulnerable assume they are at risk and leave, which further clogs exit routes.

When Hurricane Rita hit Texas shortly after those residents had watched the devastation caused by Katrina, the effect was stark: “We had everyone evacuate,” either from fear of their homes being damaged or fear of losing power for an extended period of time, says Russell Henk, senior research engineer at the Texas A&M Transportation Institute. Many of those people could have sheltered in place or locally, says Henk, a member of a post-Rita task force that aimed to improve future evacuations. And the fact that they all tried to get out made it all the more difficult for those who most needed to leave.

Timing. Another major consideration in evacuations is how much advance notice to give. That’s not so easy to calculate, as it turns out.

Hurricane Floyd hit the southeastern United States in September 1999. At the time, it prompted what was considered the largest-scale evacuation in the history of the country. Areas from Florida all the way up through North Carolina were evacuated, putting two to three million people onto the roads. In several places, traffic ground to a standstill. Baker spoke to one person evacuating in South Carolina who said that he “got on the interstate spur that comes into 95 that goes into downtown Charleston. He said for three hours he could still see his house because the traffic was creeping so slowly.”

Before Floyd, transportation analysts were mostly focused on what is known as clearance time, says Baker. Clearance time is how long it theoretically would take to get everyone out of an area from the time you tell them to evacuate—based on normal traffic. “That’s important because the local officials need to know how long they can wait to tell people to start evacuating,” Baker says.

But clearance time does not account for traffic backups. Baker explains that commute time is a measure of how long the folks will be spending on the road. And that’s important too. “The average time that people in Charleston spent commuting [from Floyd] was about ten hours. So if you’re sitting in the road for that long, especially if it’s the interstate where you can’t get off very often, then you have bathroom problems and medical problems and food problems and water problems and people running out of gasoline, and it’s just a helpless feeling for people to be sitting there and not moving at all,” says Baker. Additionally, if the backup lasts long enough, people might not be out of the area they needed to evacuate from when the storm hits.

Contraflow. One possible solution that has been tried is called contraflow. It is a method of reversing the direction of certain lanes of traffic during an evacuation or other events to make the flow out of an area more efficient. For example, if you have several lanes on a highway coming into an area that’s being evacuated, contraflow plans would appropriate some of those lanes to give people more lanes for driving out of the area.

Contraflow is being used more often in evacuation planning and has been implemented in several evacuations, including many hurricanes. There are contraflow lanes of all different lengths, according to Transportation’s Role in Emergency Evacuation and Reentry, written by Brian Wolshon, a professor in the Department of Civil and Environmental Engineering at Louisiana State University and director of the Gulf Coast Center for Evacuation and Transportation Resiliency. He has spent years studying hurricane-evacuation traffic patterns and trying to develop computer models that could predict future patterns to aid in evacuation planning. According to that book, the shortest contraflow lanes are about 25 miles long out of New Orleans, but there have been lanes of more than a hundred miles in other areas.

The data indicate that contraflow can make a major difference in evacuations. Contraflow was not implemented on a certain stretch of I-55 during Hurricane Ivan evacuations in 2004, but it was implemented on that same stretch a year later for Katrina. While only about 61,000 vehicles were able to evacuate on a northbound stretch of highway in the 48-hour evacuation period during Ivan, contraflow allowed 85,000 to get out over that same road and timeframe during Katrina, according to Wolshon’s book.

But contraflow is difficult to implement and can’t be used in all situations. Careful planning and controls have to be in place to redirect traffic. Authorities will have to determine where the entrances to the newly reversed lanes will be, and driver-awareness plans will be needed to make sure people know the lanes are changing. Additionally, contraflow can involve shutting down certain exits and funneling people toward certain areas; sometimes officials in those locations express concern that they won’t be able to accommodate all of the evacuees.

When contraflow isn’t implemented efficiently, it can be just as bad as not being done at all. Wolshon uses as an example the attempted implementation of contraflow out of New Orleans during Hurricane Ivan. Wolshon says officials built a crossover median to connect the two outside outbound lanes of I-10 with the two inbound lanes, “but it didn’t work as effectively as it could have or should have,” says Wolshon.

Wolshon and other researchers have used trafic simulation models to figure out the best places for the ingress and egress to contraflow lanes. They came up with a specific reloading model for the New Orleans area that was used during Hurricane Katrina. When that was implemented, “traffic flowed much, much better,” says Wolshon. “It wasn’t perfect but it was much better, and they had the data to back it up to show how many more people moved out of the city.”

Merging, which works fine in normal rush-hour commuter traffic, can slow things down too much when so many vehicles are attempting to leave an area, and it can be particularly tricky in contraflow areas. One option is to disallow merging at certain points along a highway. “[W]hen you get to a situation where it may be a life and death, you need to keep people moving, you might say ‘well, look, they might not be able to exit here, they might not be able to get onto this interstate exactly where they want to go, but at least they’re…going to be kept moving,’” Wolshon says.

In the case of the full-on exodus that happened in Texas with Hurricane Rita, the overflow of evacuees was exacerbated by the lack of a contraflow plan in the region, says Henk. Additionally, though people had advance warning, a lot of people waited until the end of the week to evacuate. “Basically, we just had gridlock. The whole system just cratered…people literally sat, and most of the freeways and arterials were parking lots. What usually takes maybe 30 minutes to an hour took the better part of a day in terms of movement and getting people in particular out of the Galveston [and] Houston area,” Henk says.

Fuel. Traffic isn’t the only thing that can stop evacuees in their tracks. An empty tank can have the same effect. With Rita, the gas stations hadn’t ramped up, and everyone had waited until the last minute to fill their tanks. Henk says that now gas stations are advised to get their inventories up to the maximum 96 hours before a storm is expected to hit. There are now agreements between the State of Texas and the private sector petroleum industries to fuel up before a storm. “There’s now a formal countdown starting at four days out where there’s prepositioned fuel, advanced fuel capacity, and that’s just one of the many dynamics that are now in place,” Henk says.

Additionally, in his post-Rita work, Henk recommended having large tankers prepositioned along the evacuation routes so that cars could refill tanks on the go, and he says the state implemented an awareness campaign where people receive flyers reminding them about items such as fueling up as the storms approach.

Staggered departures. Doing evacuation orders in stages or phases is another way to mitigate bottlenecks and traffic standstills. Wolshon has also been involved in helping to develop how this can be done effectively. For example, a phased evacuation was implemented in Louisiana during Hurricane Katrina, with the earliest stage of the evacuation being reserved for people south of the Intracoastal Waterway who would have been at the most risk for flooding.

Henk recommended phased evacuations after Rita, as well. And he advised that they correspond to zip codes, rather than a color-coded map, to make it clearer when people should be leaving.

Special Needs

Hurricane Katrina also revealed that Louisiana and several other areas did not have adequate plans for evacuating those who were unable to drive, did not have vehicles, or were in at-risk populations. “There was really no plan put in place to evacuate the people of New Orleans who didn’t have access to cars, which was about a third of the population,” says John Renne, who led a study titled National Study of Carless and Special Needs Evacuation Planning.

The report found that outreach must flow both ways in disaster preparation. There should be public awareness campaigns from emergency officials to ensure that the carless and those who need assistance in evacuations are aware of the resources available. Additionally, information about needs must come from the community itself so that its members can be appropriately accommodated.

In the years after Katrina, cities and states have made some progress in this area. For example, Wolshon’s book cites an online system implemented by Houston’s Office of Emergency Management that allows residents to register for special needs transportation services for hurricane evacuations.

In New Orleans, authorities have implemented the City-Assisted Evacuation plan. Residents can go on a city Web site and find information about where their evacuation spots are, as well as register for special-needs or city-assisted evacuation. “So the emergency management officials need to work with the transportation officials [and the] transportation people need to work with the local communities,” including social services and nonprofits, Renne says.

New Orleans has taken a unique approach to the awareness issue. It teamed up with a local arts council to have artists create sculptures to draw attention to the “evacuspots” where people would meet for city-assisted evacuation. “So it’s a very innovative approach to combining public art with transportation and emergency management,” Renne says.

City-assisted evacuation was tested for the first time in 2008 during Hurricane Gustav and was a success, Renne says.

Miami is also doing a good job in carless and limited-mobility evacuation preparation. “They have been working and have very detailed plans that respond to homeless populations, vulnerable populations; they work across the region all the way from the Florida Keys all the way through the entire Miami-Dade County and Broward County up the coast,” says Renne.

New Models

Researchers are continuously trying to improve traffic demand modeling that’s currently lacking in these evacuations. Chester Wilmot, professor in the Department of Civil and Environmental Engineering at Louisiana State University, has devoted much of his career to it. He is currently developing a new model that he hopes will better predict how and when people will be on the roads during a mass evacuation.

The model requires various types of information, the first being about the storm—such as intensity and projected path—and the second being what officials are doing. For example, have they issued evacuation orders? Are they opening up a contraflow? Are the orders regarded as mandatory or voluntary? The third type of information concerns peoples’ living conditions—such as whether they live in mobile homes and whether they have cars.

Wilmot’s team uses that information to determine what the evacuation behavior will be. The data fed into the model is dynamic and changes over time as the storm and other conditions change.

Wilmot’s model also uses data from post-event surveys. He gets dynamic data about each storm from the National Hurricane Center, and that is used to build up databases that can feed the models.

Wilmot’s group breaks out models for separate types of behavior. For example, one model might address whether the household would evacuate. The next model would look at where the household would evacuate to. Then there would be a model looking at the route the household would use to evacuate. Other models would look at what type of vehicle the households would evacuate in.

The models are used in a daisy chain to attempt to reproduce the total behavior of people. The goal is to predict, based on certain conditions of a storm and certain actions taken by decision makers or emergency officials, which households are likely to evacuate when, and if they do, where they would be heading and what route they would choose. “That enables you to give sort of traffic estimates,” Wilmot says.

It is hoped that the models will ultimately allow planners to anticipate route and traffic flow. However, though it’s been run using information from past storms, it is still just in a test mode. Whether it could work in real time has yet to be proven. Seeing if the simulation works in storms coming up would be the next step. But Wilmot says there are still some kinks to work out, so it’s not ready to be used in an actual planning situation just yet.

There are many aspects of behavior and transportation planning that are integral to getting people out of vulnerable areas in advance of a storm’s hitting or after there’s a disaster. And although past experiences have provided lessons that have assisted in recent years, there is more work to be done. As Wolshon says, evacuation can be an art, but there’s plenty of room for science and planning to be factored in.

Renne also notes that more should be done to connect local, state, and federal planning approaches. “Disasters don’t know political boundaries,” he says. “And we need to do a better job looking across regions and working from municipality to neighboring municipality to figure out how a region can come together and work collaboratively on these topics.”