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The NRC is also currently developing a specific set of processes and objectives that will raise the level of consistency and uniformity of such studies Jones and Wolshon Forthcoming. The U. Army Corps of Engineers approach for hurricane evacuation transportation analyses U. Army Corps of Engineers and adapted from Baker is summarized here. These processes can be readily generalized to other hazard scenarios.
Evacuation transportation zones are defined based on 1. These zones represent subareas of the region under threat and serve as the basic units of origins and destinations in the analysis. Dwelling unit data are developed for each zone based 2. These data include more detailed characteristics of the population, number of dwelling units, and number of vehicles. Such data are readily available from sources such as the U. Census Bureau. The roadways that are part of the evacuation trans Particular attention is paid to inter- sections and link segments in which reductions of outbound lanes occur.
These data are also readily available within most transportation agencies and metropolitan planning organizations in the form of geographic information systems GIS inventories. A travel demand estimate is conducted to forecast 4. Evacuation travel demand forecasting relies on the behavioral analysis. The process is used to estimate the number of people and vehicles that will go to local public shel- ters; homes of local friends and relatives; local hotels, motels, churches, and other types of local destina- tions; and all destinations outside the local area.
These trip productions are calculated for each evacu- ation transportation zone.
Crude falls as Gustav weakens
A worst-case participation rate is used to determine how long the evacuation would take if everyone ordered to leave actually did. It also results in inflation of actual or even probable. Similar to plans in Houston, the strategy seeks to sequence evacuation orders starting from the coast and moving inland. One of the interesting features of the plan, shown in the bottom legend, is that it is developed specifically for evacuation traffic management purposes and not as a protective action plan.
Part of the Louisiana plan is to incrementally implement increasingly restrictive traffic management plans. Thus, the phasing plan also establishes when contraflow plans could be expected to take effect. It is recognized that phased evacuations are not without problems of their own.
Chief among these is evacuees following procedures properly. Many evacuees tend to wait for clear evacuation orders before leaving. Thus, there can be a tendency for later evacuations, even in the early phase desig- nated areas of the plan. There is also the potential as seen in Houston for many more people than necessary to evacuate. Because it is effectively impossible to enforce phased evacu- ations, they end up as a guidance-only strategy.
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These types of conditions can be multi- plied exponentially when shadow evacuations, in which people not actually in danger also evacuate, occur. Shadow evacuation-induced gridlock that impairs the movement of upstream evacuees was observed recently in Houston during the evacuation for Hurricane Rita in Vague instructions and statements from the authori- ties, misperceptions regarding vulnerability, Peacock et al. As a result, traffic in the region came to a virtual standstill for more than a day.
In addition to causing driver frustration, using up available fuel supplies, and potentially decreasing the participation rates of future evac- uations, these conditions also limited the ability of coastal evacuees in the Galveston area to evacuate. It impaired the movement of infirm and special needs evacuees from hospi- tals and other care facilities.
To reduce the potential for similar occurrences in the future, phased evacuation plans for hurricanes have been or are being developed in several states. Phased evacuation planning for hurricanes is particularly useful because storms tend to give several days warning, allow for the most vulner- able areas to be clearly recognized, and often create massive numbers of evacuees.
The idea of phased evacuation plans is to issue sequential evacuation orders that initiate evacuations in the most threatened areas first and permit evacuees to pass through areas of higher population before the onset of road. TraFFic conTroL deVices To help in the control and guidance of traffic during evacu- ations, several transportation agencies have developed tools and strategies to convey information to travelers.
The three most common are signs, pavement markings, and traffic signals. The following sections include examples of evacua- tion-specific techniques using these devices. Chapter 21 in the manual includes guidance on the design, size, and placement of these devices. Signs in this section of the MUTCD are meant to guide, restrict, or control traffic operations and to limit access to essential emergency and aid-related vehicles. The chapter also includes suggested signs for medical, welfare, registration, and decontamination centers that may be required for various types of hurricane, radioactive fallout, chemical, and general hazards.
The EM-1 sign may be used with legends for other types of hazards than hurricanes, and this line of text may be omitted for more general use. The sign configuration shown on the left side of Figure 5 also includes a commonly used supplemental sign with AM and FM radio station frequen- cies that provide emergency information. In addition to the formally designated signs in the MUTCD, it is not uncommon for local transportation agencies to develop their own signs for local use in emergencies and evacuations. These include signs specifically created for use on contraflow segments to convey radio frequencies for evacuation travel Among the best-defined and well-developed roles of trans- portation in evacuations are in the areas of direction and control of transportation systems.
This is not surprising because traffic control and traffic operations are the areas that transportation agencies are the most experienced and best equipped to support. As a result of a series of several recent high-visibility mass evacuation problems, state DOTs across the United States have begun to take much more active roles in planning regional evacuations and, in some cases, have served lead state agencies in the development of management and control strategies.
There is also a trend among DOTs to employ dedicated full-time staff members whose primary responsibility is maintaining evacuation readiness and coordination with other state agencies. These personnel have proved to be valuable in establishing and maintaining communications and coordination with neighboring states where evacuations cover multistate regions and where evacuation monitoring and control takes place from regional and statewide traffic management centers.
Two illustrations for which these measures have been particularly useful are for the complex regionwide freeway management plans that are now in place for New Orleans and Houston. The DOTs in Louisiana and Texas were instrumental in development of the plans, both of which now incorporate coordinated evacuation phasing, contraflow, and assisted evacuations. The direction and control of transportation systems should not, however, be interpreted as extending into the direction and control of evacuations, directly.
Although transportation agencies play key roles in supporting and assisting in the execution of such orders, the review of practice showed that the declaration and timing of evacuations are decisions that are made by emergency mangers and law enforcement agen- cies and that there were no examples in which transportation agencies were involved in such decisions.
Instead, transpor- tation support activities were limited to actions such as the reconfiguration and implementation of traffic control, traffic management planning, and areawide traffic monitoring, among many others. This chapter summarizes and highlights many current practices and recent developments in traffic control and the role that transportation agencies play in supporting plan development and decision making in emergency evacuations. This sign, located just before a key decision point outside of New Orleans, was used to guide drivers into the appropriate lane based on their desti- nation.
At this location, the left two lanes are guided into the contraflow lanes west toward Baton Rouge, whereas the right two lanes continued in the normal flow lanes northbound toward Mississippi. An example of a less sophisticated, though highly useful sign is shown in Figure 9. Although this sign is not used on an evacuation route, these flood-level gauges signs are common in evacuation routes in New Orleans where roadways are prone to flooding. These passive flood depth measurers give drivers an idea of the depth of water in low-lying areas near underpasses.
In Figure 9, the horizontal line shows the flood depth at this underpass location sustained during the landfall of Tropical Storm Allison in As with some of the previously mentioned signs, these markings are not found in the MUTCD, but rather they have been developed for local use.
Pavement markings for evacuations are much less common than signs. Because they are not included in the MUTCD, no formally established stan- dards guide their design and implementation. Signing on contraflow segments is particularly important along the reverse flowing side of contraflow freeway lanes. When the alignments of directional freeway lanes become independent or separated by medians, drivers in contra- flowing lanes may not always be aware of exit locations and services available, because they cannot see into the other lanes and the signs in their lanes face the opposite direction.
When not in use, these signs are folded upward and appear as blank sign backs as shown on the left side of Figure 6.
When needed, a crew unlocks the latches permitting the bottom half of the sign to fall into the open position and secures the bottom sign half to the sign supports see the right side of Figure 6. To maintain readiness for the implementation of traffic control devices during the hurricane season, ALDOT, as with several other states, also maintains ready-for-use mobile transport vehicles for rapid deployment. An example of one of these vehicles, loaded to implement contraflow on I, is shown in Figure 7.
The difference is the addition of a directional arrow above the hurricane symbol to indicate the intended direction of travel. The review of practice showed that some new types of heat-applied thermoplastic pavement markings retain their retro-reflective properties even when submerged below two or three inches of water.
Thus, they may be desirable on routes prone to flooding during evacuations. An example of pavement markings used to designate shoulders for use as an additional travel lane is shown in Figure On the left side of the figure is the marking used for the inside shoulder adjacent to the normal flowing lanes.
These markings are particularly important in advance of interchange ramps as the paved shoulder aligns with the off- and on-ramp auxiliary lane.
The review of practice showed that, currently, there are no standardized or recommended rules of operation for traffic signal control during evacuation emergencies. Although it is recognized that the primary goal should be to facilitate the outbound movement of traffic away from the hazard zone, it is also recognized that as in nonemergency conditions cross- street turning traffic needs to be accommodated.
In urban- ized areas with densely spaced street grids, it is possible that primary movement may not be clearly defined. This lack of definition has been controversial. An example of such an issue was noted in recent hurri- cane evacuations for the timing of signals along primary arterial highways in less densely populated areas. In several instances, evacuation traffic on the major highway passed through small towns with one or two traffic signals.
In some cases, signal indications along the primary highway were set to a flashing yellow to maintain uninterrupted flow along the main route. However, this caused some areas of these small towns to become inaccessible as local travelers were unable to find adequate gaps to cross the major highway. To avoid similar conditions in later evacuations, some localities have maintained normal, nonemergency, peak-hour signal timings to service cross-street traffic. Note: the horizontal line indicates the 8-ft flood depth during tropical storm allison in Contraflow is a form of revers- ible traffic operation in which one or more travel lanes of a divided highway are used for the movement of traffic in the opposing direction.
The common definition of contraflow for evacuations has been broadened over the past several years by emergency management officials, the news media, and the public to include the reversal of flow on any roadway during an evacuation AASHTO It is a highly effec- tive strategy because it can both immediately and signifi- cantly increase the directional capacity of a roadway without the time or cost required to plan, design, and construct addi- tional lanes.
It is also popular with the public because it is viewed as a logical utilization of the unused lane capacity of adjacent inbound lanes as shown in Figure Since , contraflow has been planned to evacuate regions of the southeastern United States when under threat from hurricanes. As a result of its recent demonstrated effec- tiveness during Hurricane Katrina Wolshon , it is also now looked upon as a potential preparedness measure for led to congestion, long queues, and delays as well as the potential for prohibiting full clearance of the hazard zone. To address these issues, some state agencies now plan to use flashing yellow in conjunction with police enforcement to permit cross-street traffic maneuvers.
A recent study conducted by Chen et al. Simulations were performed on two arterial corridors over a hr period using cycle lengths of , , and s as well as all-yellow and all-red flashing modes. The results quantified the trade-off between network clearance time and delays for cross-street traffic. As expected, the longer green times for the outbound evacuation traffic was best for maximizing the amount of outbound evacuation traffic volume and minimizing their delay. Although the authors recommended a flashing yellow to give a virtual infinite green to the evacuation traffic, they also pointed out that, if approach volumes are closer to those of routine peak periods, the usual nonemergency timing plans could be most effective.
If average delays of 15 min to cross-street traffic were deemed to be acceptable, then cycle lengths FigURE 10 hurricane evacuation route directional shoulder pavement markings normal lanes at left and contraflow lanes at right , Us, texas. Note: photos not taken under evacuation conditions. Reverse and contraflow operations have also been popular for managing the infrequent, but periodic and predictable, directionally imbalanced traffic patterns asso- ciated with major events such as concerts, sporting events, and other public gatherings.
Reversible lanes have been cost- effective on bridges and in tunnels where additional direc- tional capacity is needed, but where additional lanes can not be added easily.