Brian Wolshon

National review of hurricane evacuation plans and policies: a comparison and contrast of state practices

Since the involvement of transportation professionals in evacuation has been a fairly recent development, it is not surprising that the level of understanding of evacuation issues and terminology in the transportation community is somewhat limited. It has meant that many of the newly developed plans and policies have never been put into actual practice. It has also meant that many aspects of these plans and policies vary significantly from state to state and remain largely unknown to the wider professional transportation community. To determine what the latest policies and strategies are, how they differ from one location to another, and to increase the level of knowledge and awareness of these new evacuation practices, a national review of evacuation plans and practices was recently undertaken by researchers from Louisiana State University (LSU) in cooperation with the LSU Hurricane Center. The study was carried out from a transportation (rather than an emergency management) perspective and included both a review of transportation literature and a survey of department of transportation (DOT) and emergency management officials in coastal states threatened by hurricanes. This report summarizes the findings of the survey while also providing some background on development of evacuation practices and research in the US. This report includes information on the application of evacuation strategies and technologies, such as the use of reverse flow operations and intelligent transportation systems (ITS). It also summarizes current evacuation management policies, methods of information exchange, and decision-making criteria. The intent of this report is to provide a broad perspective on the current state of evacuation practices, while also presenting similarities and differences in individual state practices. Particular attention is paid to unique, innovative, and potentially useful practices used in individual states that could be more widely applied.

Alternative Methods to Increase the Effectiveness of Freeway Contraflow Evacuation

The city of New Orleans is among the most vulnerable cities in the world to the threat of hurricanes. To protect its population from these storms, officials in Louisiana have joined a growing number of states that are planning to use contraflow freeway operations to expedite the evacuation of threatened areas. Although contraflow is widely regarded as a major advance in evacuation planning and response, no one really knows how well, or even if, it will work. Research was undertaken to improve the understanding of traffic conditions on contraflow freeway segments during an evacuation. The CORSIM microscopic traffic-simulation program was used to model the freeway configuration that will be used to evacuate New Orleans as well as two alternative scenarios for this same segment. The results showed that the currently proposed configuration might result in an underutilization of the contraflow segment, thus significantly limiting the number of evacuees who can get out of the city. The study also showed how the effectiveness of the New Orleans contraflow segment might be significantly improved with some simple and inexpensive modifications to the existing plan. Most important, the results of the research underscore the critical nature of proper planning and design of contraflow entry points and how they are often overlooked for both emergency and nonemergency conditions.

Modeling and performance assessment of contraflow evacuation termination points

About 20 hurricane evacuation contraflow segments are planned for use in the United States. When activated, these routes will serve as lifelines for people fleeing the potential destruction of approaching storms. The termination points of these segments are critical because they move traffic from the reverse-flowing lane into the normal flow direction. They are also thought to affect the overall effectiveness of the sections significantly because they can regulate the amount of volume that exits the section. The research effort described in this paper was undertaken to assess and compare the operational characteristics of contraflow evacuation termination point designs that would be used under threat from catastrophic storms. Among the developments of the research was an approach and set of assumptions for using CORSIM to model contraflowing freeway traffic under evacuation conditions. These models were used to assess and rank the planned termination designs comparatively and to identify the factors that ...

ANALYSIS OF INTERSECTION DELAY UNDER REAL-TIME ADAPTIVE SIGNAL CONTROL

The United States Department of Transportation has recently begun implementation of the national demonstration project for suburban Advanced Traffic Management Systems (ATMS) utilizing the Sydney Coordinated Adaptive Traffic System (SCATS). SCATS is an automated, real time, traffic responsive signal control strategy. The expected benefit from the system comes from its ability to constantly modify signal timing patterns to most effectively accommodate changing traffic conditions. The objectives of this research study were to analyze the differences in certain delay parameters which would occur as a result of implementing SCATS signal control. The study employed a macroscopic simulation procedure to compute intersection delay under both a strategy that changed signal timings once per hour and SCATS signal control. A comparison of delay under both forms of control is presented. The study findings demonstrated mixed results regarding the benefit of SCATS control. A general conclusion of the study was that SCATS distributed the delay across competing approaches more evenly. However, in some cases this resulted in an increase in the total intersection delay. The observed delay change was attributed primarily to the saturation equalization objective of the SCATS control program. SCATS attempts to allocate green time to the intersection approaches based on the degree of saturation. Under this philosophy the system is able to balance the percentage of green time between all approaches, resulting in more uniform delay.

Transit-Based Emergency Evacuation Simulation Modeling

Several recent mass evacuations, including those in advance of Hurricane Katrina in New Orleans and Hurricane Rita in Houston, have demonstrated the effects of limited planning for carless populations. The lack of planning left a significant portion of the mobility-limited population of both these cities unable to flee in advance of the storms. Since 2005, however, both of these cities (as well as others across the United States) have developed transit-assisted mass evacuation plans at various levels of detail. Because these plans are relatively recent and do not have a history of experience on which to base their performance, it is difficult to know how well, or even if, they will work. This article describes one of the first attempts to systematically model and simulate transit-based evacuation strategies. In it, the development of and the results gained from an application of the TRansportation ANalysis and SIMulation System (TRANSIMS) agent-based transportation simulation system to model assisted evacuation plans of New Orleans are described. In the research, average travel time and total evacuation time were used to compare the results of a range of conditions over a two-day evacuation period, including two alternative transit evacuation routing plans and four alternative network loading scenarios. Among the general findings of the research was that the most effective scenarios of transit-based evacuation were those that were carried out during time periods during which the auto-based evacuation was in its “lull” (nonpeak/overnight) periods. These conditions resulted in up to a 10% reduction in overall travel time and up to 45% reduction in the total evacuation time when compared to peak evacuation conditions. It was also found that routing buses to alternate arterial routes reduced the overall travel time by up to 52% and the total evacuation time by up to 14%.

Empirical Characterization of Mass Evacuation Traffic Flow

Among the many gaps in the current state of mass evacuation planning and analysis practice has been a lack of the field-based study of traffic flows under actual evacuation conditions. Without observational studies of such conditions, the simulations and forecasts of roadway performance during emergencies have historically been based on conjecture and professional judgment. However, the recent series of hurricane evacuations along the U.S. Gulf Coast has given investigators the opportunity to collect and evaluate traffic conditions during evacuation scenarios. This paper uses recently collected traffic data from two recent evacuations in Louisiana to assess how well various roadway classifications in different geographic areas were able to carry traffic during emergencies under both normal-flow and contraflow operations. The objectives were to characterize the general conditions of traffic flow under an evacuation condition, to address lingering questions related to maximum sustainable flows, and to examine how the flows compared with those suggested in the Highway Capacity Manual (HCM). The findings of this work suggest that during evacuations most roadways carry flows well below the HCM-predicted maximums and that despite the enormous demand conditions generated by a mass evacuation, the maximum flows on urban roadways typically do not even reach those of typical daily commuter periods.

Modeling risk attitudes in evacuation departure choices

The decision of whether and when to evacuate can be characterized as decision making under risk. Presently, most models assume linear utility functions through which it is impossible to disentangle factors that influence risk attitudes and other factors that affect decision making under risk. There is a need to disentangle and study factors that affect risk attitudes from factors that affect an evacuees preparation time. The aim in doing so is to provide planners and practitioners with an ability to measure a persons risk attitude and develop appropriate strategies that could motivate people to evacuate. This study is expected to connect the theory of risk developed in economic theory with behavior under threat. The paper uses the Hurricane Andrew response data in conjunction with time-dependent data on the probability of a hurricane strike and the category of the hurricane data to develop a model for evacuation departure choice. A constant relative risk aversion specification is used to model risk attitudes. The process of an evacuation is abstracted as an individual being given a choice between two lotteries: either to stay or leave. The results show that the model is able to predict the total number of evacuees and the time varying evacuation rates with reasonable accuracy. Factors such as time of day, length of time spent in a region, and whether a mandatory evacuation order was issued affected risk attitudes. The presence of children affected the amount of time spent preparing if the family decided to stay.

Validation Techniques for Region-Level Microscopic Mass Evacuation Traffic Simulations

The experiences of several recent evacuations have demonstrated how a mass evacuation of a major city can affect traffic throughout an entire region. This realization has brought the need for analyzing and evaluating evacuation plans at a regional level. Numerous recent studies have devoted themselves to the topic of simulating large-scale evacuations. However, few studies have developed procedures for the validation of large-scale models. This paper discusses validation within the context of the recent development of the regional multimodal evacuation model for New Orleans, Louisiana. The New Orleans model is unique because it is among the first ever to incorporate qualitative and quantitative model validation procedures based on field data collected during an actual mass evacuation. The paper discusses the various statistics considered for validation, including their inherent advantages and disadvantages. It also presents the results obtained from the validation exercises of the New Orleans model. The study concluded that regression analyses were the most appropriate for statistically analyzing the spatial and temporal data correlations between the traffic patterns produced within the simulation and those actually observed during the Hurricane Katrina evacuation. From a qualitative standpoint, colorized spatiotemporal maps were also found to be quite effective for visualizing traffic speed and volume patterns. The maps were also invaluable for quickly identifying and analyzing bottleneck areas at both the local and regional levels.

Performance of Traffic Networks during Multimodal Evacuations: Simulation-Based Assessment

Mass evacuations of urbanized areas can be expected to generate traffic demand significantly in excess of routine daily travel conditions. Depending on the nature of the hazard and the population characteristics within the threat area, the elevated demand conditions may last for several days and can impact thousands of miles of roads. This paper presents the results of a project to evaluate the impact of a transit bus-based evacuation on the operation of a regional road network during a mass evacuation. In the project, the TRANSIMS agent-based simulation system was used to model the Citizen-Assisted Evacuation Plan (CAEP) for the City of New Orleans within the context of a general evacuation. Regional plans developed by Louisiana officials to support the evacuation of low-mobility individuals when under threat of hurricanes were used to code the model. However, because these plans have yet to be fully implemented, their benefits, effect on the overall evacuation operation, and the adequacy of the service they will provide has not been evaluated. In this the operational traffic characteristics of the busses and other vehicles involved in the evacuation operation were simulated under a range of conditions. The results showed that while the CAEP busses were able to increase the total number of people evacuated from the threat area, the additional vehicles had a minimal impact when they were routed exclusively to arterial evacuation routes. However, when bussed were routed to more heavily utilized freeways, travel delays increased and congestion queues increased by about 50 percent.

Traffic Impacts and Dispersal Patterns on Secondary Roadways during Regional Evacuations

The evacuation of southeast Louisiana in the days prior to Hurricane Katrina represented the largest concentrated movement of traffic in the history of the state. Traffic data showed that nearly a half million vehicles, carrying an estimated one million people, flowed out of the New Orleans area before the storm. Since it was well recognized that evacuation traffic would overwhelm the available network capacity, Louisiana transportation and state police officials developed a plan to achieve a maximum utilization of the states highest capacity evacuation routes. This paper differs from prior analyses by shifting the focus of attention from the impact of evacuation traffic on freeway and primary arterials to secondary and low volume roadways that have historically been underutilized during such emergencies. Analyses were conducted to determine how traffic was dispersed on the secondary roadway network, how long the impacts lasted, and where they were the most pronounced. The results suggest that many Katrina evacuees used roads in the secondary system as their primary routes of egress to far greater degrees than previously thought. They also indicate that secondary and low volume routes were also well used as alternatives to saturated interstate freeways and by evacuees seeking destinations not directly served by the primary highway network.