NUREG/CR--4831

PNL.-7776

State of the Art in Evacuation

Time Estimate Studies-for

Nuclear Power Plants

Prepared by

T. E. Urbanik, J. D. Jamison

Pacific Northwest Laboratory

Operated by

Battelle Memorial Institute

Prepared for

U.S. Nuclear Regulatory Commission
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NUREG/CR-4831

PNL-7776

State of the Art in Evacuation

Time Estimate Studies for

Nuclear Power Plants

Manuscript Completed: February 1992

Date Published: March 1992

Prepared by

T. E. Urbanik*, J. D. Jamison

Pacific Northwest Laboratory

Richland, WA 99352

Prepared for

Division of Radiation Protection and Emergency Preparedness

Office of Nuclear Reactor Regulation

U.S. Nuclear Regulatory Commission

Washington, DC 20555

NRC FIN 12000

*Consultant, College Station, TX 77845-9627

ABSTRACT

In the event of a major accident at a commercial nuclear power station, exposure of the public to airborne

radioactive materials can be prevented or greatly reduced by evacuating the area immediately surrounding

the reactor site. Reactor licensees are required to conduct studies to estimate the time needed to evacuate

the public from the area surrounding each nuclear power station. The results of such studies are used by

regulatory personnel and emergency planners to assess the potential effectiveness of protective responses

for the public. The time required to evacuate the public from a 10-mile emergency planning radius is

estimated by analyzing the available transportation facilities and other relevant conditions within this

radius. To support the analysis, data must be collected and assumptions must be made regarding the

transportation facilities, the size and characteristics of the population and other conditions in the planning

zone. This report describes standard approaches and provides recommendations regarding the relevant

information, assumptions and methods to be used in performing evacuation time estimate studies.

iii

CONTENTS

Abstract ...........

Introduction .........

Transportation Analysis

Basic Methodolo

Emergency Planr

Scenarios ....

Demand Estimat

Capacity .....

Adverse Weather

Accidents ....

Traffic Managem

Roadway Constr

Driver Behavior

Radial Dispersio

Relocation Cent

Trip Generation

Analysis 'Ibols

Other Considerations in

Assumptions aba

Populations Dep

Special Facility I

Confirmation Ti

State and Local

Reporting ...

Updating ....

References ...

1 Traffic Management Di

1 Notification Distributi

2 Preparation Distributic

3 Trip Generation Time

........... Csr ............................................

Cos......... ...............................................

•igy Zondera ns. .............. ........ ..... ............ ........

ing . . ...... . . . . . . . . .. .. . . . . . . . .. . . .. . .. . . . . . . . . . . . . . . . . . . . .

r. . .. .e . . . . . . . . . . .. . . . . . . . .. . . . . . .. . . . .. . . . . . . . . . . . . . . . .

.i nt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

tion...................................................

rn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

r s. . .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

T ent . . . . . . . . . . . . . . .. . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

E c uto ............................................ .........

)u t E a i.............................................. .......

end.........................................................

. . .i . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

T im e .. ............................... ......... ............

e im e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Evacuation Time Estimate Studies ...............................

out Evacuation Tim e ..........................................

•endent on Public Tr1ansport .....................................

Populations .................................................

m e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

R eview ....................................................

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . °. . . . . . . . . . ..

FIGURE

iagram .....................

TABLES

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6

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v

INTRODUCTION

Evacuation is used as a protective action to

remove people from areas potentially affected by

wind-borne radioactive materials released from

nuclear power plants. To prepare for evacuation,

emergency responders can use time estimate

studies to develop appropriate protective

responses for potential events and to find ways to

reduce evacuation time. This report, prepared by

the Pacific Northwest Laboratory for the U. S.

Nuclear Regulatory Commission (NRC), provides

information about what is needed in a useful time

estimate study. This report discusses both transportation analysis, the primary concern in a time

estimate study, and other considerations, such as

populations with special transportation or housing

needs.

Before 1980, transportation analysis for natural

and technological hazards was rarely done. The

determining factors in evacuation times were

considered largely qualitative and rarely quantifiable. Techniques for determining evacuation

times were devoid of the expertise that existed in

transportation analysis. In 1980, the NRC and

the Federal Emergency Management Agency

(FEMA) issued the Criteria for Preparation and

Evaluation of Radiological Emergency Response

Plans and Preparedness in Support of Nuclear

Power Plants, NUREG/CR-0654 (NRC 1980a and

1980b). This document established planning

standards and evaluation criteria for emergency

response plans; including those relating to

evacuation. Appendix 4 of NUREG/CR-0654

provided limited guidance on preparing evacuation time estimate studies.

Concurrently, the NRC examined techniques for

estimating evacuation times at nuclear power

plants, with results documented in Analysis of

Techniques for Estimating Evacuation Times for

Emergency Planning Zones, NUREG-CR-1745

(Urbanik et al. 1980). This document made recommendations on how to conduct evacuation

time estimates. These recommendations, along

with work by FEMA contractors, were included in

Revision 1 of NUREG/CR-0654.

Because there may be a wide range of potential

accidents, it is impractical to provide time

estimates for each of the possible accident and

condition possibilities. Thus, it is appropriate to

think of evacuation time estimates as part of a

planning basis for each site, i.e., as part of the

larger plan for responding to a spectrum of

possible accidents. (For details about using a

planning basis to develop an emergency response

plan, see NRC [1980b and 1978].) The standard

planning basis includes a plume exposure pathway

emergency planning zone (EPZ) of about

10 miles radius; this is the area for which detailed

evacuation planning is considered appropriate.

Within these spatial limits, evacuation time

estimates examine the sensitivity of evacuation

times to key variables, including the nature and

limits of transportation facilities in the affected

area and other factors that may affect evacuation

time, such as the public's use of public transportation or need for special transportation (e.g.,

guarded transportation). Both transportation

analysis and ancillary concerns are covered in the

following sections.

TRANSPORTATION ANALYSIS

CONSIDERATIONS

At the most fundamental level, transportation

analysis compares evacuation demand (i.e., the

number of evacuating vehicles) with available

capacity of evacuation roadways. However, the

analysis is complicated by the fact that capacity

cannot be stored for future use. That is, if

vehicles are delayed in one portion of the

roadway network, it is possible that capacity in

another portion of the network could be unused.

Simple analysis techniques exist (e.g., see the

Transportation Research Board's Highway

Capacity Manual [1985]) for evaluating operations

at various points along a roadway system.

Although not specifically intended for estimating

evacuation time, the techniques can be used to

estimate roadway capacity. However, as the

complexity of a roadway network and the number

of evacuees increase, the use of computer models

becomes attractive.

1 NUREG/CR-4831
It is important to note the inappropriateness of

using "level-of-service analysis" to do evacuation

planning. Level-of-service analysis is predicated

on the desire to provide capacity in excess of

expected demand. Ensuring that there is

sufficient capacity to provide a high level of

service during an evacuation is not practical in

most cases. Only in very low-population

emergency planning zones will a high level of

service during evacuations be achievable.

The basic methodology for estimating evacuation

times is to compare the evacuation demand (in

numbers of vehicles evacuating per hour) with

available roadway capacity or transportation

service rate. If the transportation service rate

(also typically expressed in units of vehicles per

hour) is greater than the rate of evacuation

demand, no significant traffic-related delays

would occur. In such a case, evacuation time is

simply the time required by evacuees before

beginning to evacuate, plus the time required to

drive out of the emergency planning zone.

However, if evacuation demand exceeds capacity,

additional time is required to account for trafficrelated delays. The following sections discuss the

key factors affecting evacuation time estimates.

Basic Methodology

The basic method to determine evacuation time

is to check whether the time-dependent

evacuation demand rate exceeds the available

roadway capacity. If the evacuation demand rate

is less than available roadway capacity, evacuation

time is simply the time required for the last

evacuee to begin evacuating, plus the driving time

to leave the area. A critical part of evacuation is

the trip departure time discussed in below. If the

rate of trip departures exceeds available roadway

capacity, the time required by the excess vehicle

demand must be added to the evacuation time.

A simplistic example illustrates the process. If

1000 vehicles attempt to evacuate in a 1-hour

period and available roadway capacity is 2000

vehicles per hour, there is no significant roadwayinduced delay. Evacuation time is essentially

1 hour plus driving time out of the evacuation

area. Alternatively, if 3000 vehicles attempt to

evacuate in a 1-hour period and available

roadway capacity is 2000 vehicles per hour, the

evacuation time for the last vehicle to leave is 1.5

hours (which includes 30-minutes delay time) plus

driving time out of the evacuation area.

Obviously, a real example is more involved due

to the complexities of vehicles leaving many

different areas at many different times over many

different roads under a variety of weather

conditions. Nevertheless, the methodology simply

requires an analysis of all the routes and any

delay because of evacuation demand rates

exceeding the capacity of the roadways.

Emergency Planning Zones

A plume exposure emergency planning zone of

about 10-miles radius is required for the area

covered by evacuation planning (see NRC 1980b

and 1978). The EPZ boundary is often increased

or decreased slightly to conform to the

characteristics of a particular site. Factors

considered in determining an EPZ are

demography, topography, natural barriers, land

characteristics, access routes, and local

jurisdictional boundaries.

Sectors are sub-areas of the EPZ. The sectors,

usually 90 degrees and sub-divided at 2 and 5

miles, provide a convenient frame of reference

within which to carry out partial evacuation of the

EPZ based on wind direction. The prevailing

wind direction at the time of a radiological

release determines the affected sectors. The

sector boundaries are also based on demography,

topography, land characteristics, access routes,

and local jurisdictional boundaries.

Scenarios

Scenarios are the alternative sets of input

variables that represent combinations of

conditions that might occur at the time of a

nuclear power plant accident. For purposes of

evacuation time estimating, key variables are

typically population and roadway capacity. It is

NUREG/CR-4831 2
desirable for the evacuation time estimate study

to provide a range of evacuation times based on

the likely ranges of conditions. The evacuation

time for any set of conditions not specifically

analyzed in the study can be inferred, based on

an understanding of how evacuation time is

affected by each of the variables..

For a given geographic area, the population to be

evacuated is highly time-dependent. For

example, scenarios to be analyzed should reflect

different seasons of the year, days of the week,

and times of day. Likewise, roadway capacity is

highly dependent on weather conditions.

Weather conditions to be considered should

include both good conditions (clear) and adverse

conditions (rain, fog, or snow). Adverse weather

reduces vehicle speeds. (See page 5, below.)

The purpose of formulating several different

scenarios is to determine if certain combinations

of conditions cause evacuation demand to exceed

roadway capacity. A range of possible combinations should be considered; however, it is not

useful to analyze illogical or mutually exclusive

combinations of conditions, such as a large

daytime beach population and snow-covered

roads. The analyst should attempt to identify

that combination of conditions likely to generate

the highest typical demand on a recurring basis.

Scenarios to be analyzed should also include

periodic events or conditions that generate a

large, temporary population in the EPZ.

There is a relationship between evacuation time

and the advisability of certain protective action

decisions. Overestimating evacuation time, for

instance, is not desirable because such an

estimate might lead the decision-maker not to

order evacuation as a protective action when it is

actually the best alternative. It is also not

necessary or desirable to determine a "worst

case" evacuation time. The worst case would

nearly always be one in which evacuation is

simply not possible.

Demand Estimation

One of the key aspects of the methodology is to

define the number of evacuees. Although the

object of evacuation is to remove people from the

EPZ, it is the number of evacuating vehicles that

determine if any transportation-related delays are

likely. An estimate of the number of evacuating

vehicles can be based on several possible data

sources. In most cases, the number is estimated

after estimating the number of evacuees.

Occasionally, it is more appropriate to estimate

the number of evacuating vehicles directly. For

example, it may be more accurate to determine

the number of vehicles at a beach by counting

them in the parking lots than to count or

estimate the number of individuals on the beach.

Databases may be used to estimate of the

number of evacuating vehicles. The evacuating

population is typically subdivided into three

groups: permanent residents, transients and

special facility populations. Some individuals may

be members of more than one group.

Permanent residents are those persons who live

in the EPZ year-round. The permanent resident

population is typically estimated from census data

(often updated for local growth).

Transients are visitors, including tourists and daily

employees, who live outside the EPZ. Transient

populations are usually derived from other local

sources of data. In some cases, special field

studies, such as counting the numbers of tourists'

vehicles, may be conducted in specific areas in

order to develop better estimates of those areas'

transient populations.

Special facility populations, including school and

prison populations, are estimated on a facility-byfacility basis because the transportation needs are

determined by individual facility characteristics.

Some special-facility populations may require

buses, and others ambulances. Therefore,

consideration of individual facilities is necessary

3 3 NUREG/CR-4831
because of the need to identify the specific vehicle

requirements. Evacuation time for special-facility

populations is determined by the vehicle needs,

mobilization time, loading time, and travel time.

For example, if enough buses are available to

evacuate schools in a single trip, evacuation time

depends primarily on mobilization time of the

buses, loading time, and travel time out of the

emergency planning zone. If multiple trips are

re quired due to vehicle limitations, the analysis is

more complicated (see "Other Considerations"

on populations depending on public

transportation).

The issue of double counting makes careful

analysis necessary. In some cases, 'double

counting is necessary and does not cause

significant problems. For example, school

children are counted both as permanent residents

and as special facility populations. This is

because in some cases the school children may

evacuate from school (on weekdays in the winter

and in the daytime) and in others from home

(e.g., in the summer on an evening). The school

children are counted separately in order to

determine vehicle needs for a direct evacuation

from schools. This particular type of double

counting has no adverse effect on evacuation time

estimates; however, care should be taken to avoid

inappropriate double-counting.

Returning commuters are permanent residents

who work outside the EPZ and return home

before evacuating as a family group. Returning

commuters move in a direction opposite to the

general evacuation during the early portion of an

evacuation while the public is preparing to

evacuate. Trip generation time includes the

returning commuter trips. Returning commuters

are not considered evacuation trips for purposes

of estimating evacuation time.

Voluntary evacuation covers those who decide to

evacuate without being advised to evacuate. The

terms "spontaneous evacuation" and "shadow

evacuation" are also applied to this phenomenon.

Voluntary evacuees can be individuals living

within the planning zone but not within the

sector(s) where evacuation has been advised, or

those living outside, but near, the EPZ who may

be responding to an evacuation order directed at

people within the EPZ.

Two activities can be planned to account for

voluntary evacuation. First, traffic can be

controlled to direct voluntary evacuees so they do

not interfere with other evacuating traffic. .In

some cases, traffic control is unnecessary because

*the path of voluntary evacuees is independent of

the designated evacuation routes. Second, the

appropriate number of voluntary evacuees can be

included in the evacuating traffic demand

estimate.

Another possible demand on roadway capacity

during an evacuation is "background traffic,"

which describes vehicles in the EPZ during an

evacuation but not associated with permanent

residents, transients, or special facility

populations. The most common example of

background traffic would be through-traffic on

major intercity routes such as interstate highways.

Access control measures to direct through-traffic

onto some alternative route outside the EPZ is

the preferred method to handle this sort of

background traffic. Through-traffic not rerouted

before it enters the EPZ must be considered part

of the evacuating traffic for purposes of

calculating demand on the available roadway

capacity.

Some individuaP kiy choose not to evacuate.

Nevertheless, i ~cuation time estimate

studies, it is noniially assumed that all individuals

evacuate the EPZ.

Capacity

Transportation analysts classify roadways using

the hierarchy of local'streets, collectors, arterials,

and freeways. Local streets primarily provide

access to individual residences. Collectors

concentrate local traffic and, ideally, provide

access to arterials. Arterials are the roads and

streets whose principal function is to move traffic.

Freeways are a special type of arterial with

NUREG/CR-48314 4
controlled access. bottleneck at the capacity flow rate.

The primary evacuation roadway system for

analysis purposes generally includes arterials and

freeways. Occasionally, collectors or even local

streets are used to. improve the operation of the

evacuation roadway system. Opportunities to

improve an evacuation by using any roadway that

could reduce evacuation time should not be

overlooked; for instance, through traffic

management, a minor roadway such as a local

street could be used to 'improve evacuation

capacity.

It is unnecessary to analyze all roadways in an

EPZ because the critical elements of the

evacuation roadway system are those points

where large volumes of traffic converge. Delay

on the evacuation roadway network (if it exists)

generally occurs at the convergence of two

arterials or at arterial access to freeways.

To determine roadway capacities, the roadway

characteristics (number of lanes, lane widths,

shoulder widths, grades, etc.) and traffic control

features (traffic signals, stop signs, lane use

restrictions, one-way streets, etc.) must be

determined through field surveys. Maps and

other available databases should not be relied on

without field verification.

The quality, or level-of-service, of roadways is

quantified using a rating scheme to describe the

quality of traffic flow on a scale from A (best) to

F (worst). The level-of-service designation is not

particularly applicable to evacuations because the

issue in evacuation is how long it will take to

clear a given area, not the quality of traffic flow.

By definition, where demand exceeds capacity,

the level-of-service is "F", which is breakdown or

forced flow. The existence of level-of-service "F"

means that there are bottlenecks due to

evacuation demand that exceeds the rate at which

a roadway can accommodate traffic without delay.

Although level-of-service "F" exists upstream of a

bottleneck, the bottleneck itself, in fact, flows at

capacity. Vehicles in forced-flow conditions are

simply waiting for their opportunity to pass the

The points of a roadway with the least capacity

constrain the capacity of the evacuation network.

Typical bottlenecks are intersections, especially

intersections with traffic signals. Traffic signals

assign right of way and determine the capacity of

the intersection for movement in a particular

direction. The capacity for a given movement is

determined by the percentage of time the traffic

signal is green. Occasionally, sections of a

roadway between intersections may have fewer

lanes than other portions of the roadway and thus

create bottlenecks at locations other than

intersections. Ramps to freeways may also limit

the capacity of the freeway to accommodate

traffic. A freeway that would have at least two

lanes in each direction can never reach capacity

with a single one-lane, entrance ramp. Of course,

if evacuation traffic has more than one access

point to a freeway, the freeway itself may reach

its capacity.

Adverse Weather

The time required to make a roadway suitable

for evacuation must be added to the calculated

.evacuation time. Adverse weather conditions

(rain, snow, ice, and fog) reduce both roadway

capacity and the speed of vehicles. Severe snow

or ice conditions can make a roadway impassable.

Thus, the impact of adverse weather conditions

should be assessed at the time a decision to

evacuate is being made.

A few studies have addressed roadway capacity

under adverse conditions (Jones and Goolsby

1969, Kocmond and Perchonok 1970, Gandhi

1972, Ries 1981, and Hall and Barrow 1988). It

has been observed that rain reduces capacity 10

to 20 percent; snow reduces capacity 10 to 30

percent. The effect is determined by the intensity

of the rain or snowfall; the larger-capacity

reductions have occurred for rates of rain or

snowfall that are likely to be of brief duration.

Weather-related capacity reductions of 20 to 25

percent are typically used in current evacuation

studies.

5 5 NUREG/CR-4831
Accidents

Evacuation time estimate studies normally

include no special analyses of the effects of traffic

accidents because accidents and breakdowns are

relatively rare events. During an evacuation,

accidents and breakdowns are so few (no more

than in normal traffic) that there is no realistic or

useful way to account for their effect. Planners

usually minimize the potential impact of traffic

accidents and breakdowns on evacuation time

estimates by providing for tow trucks to remove

disabled vehicles if necessary. The rapid

clearance of damaged or stalled vehicles will ease

any negative effect on roadway capacity.

evacuation time. However, traffic management is

a resource-intensive process and its potential to

improve evacuation traffic flow is usually limited

by the availability of personnel and equipment.

Traffic control plans must detail the locations,

strategies and resources required to carry out

specific traffic management activities so that

personnel carrying out those activities understand

the goals. A traffic management diagram such as

that shown in Figure 1 is an example of how to

provide the necessary information to the

personnel who will carrn out the traffic

management plan for a specific intersection.

Traffic Management

The most typical means of reducing evacuation

time is traffic management. Traffic management

involves traffic control by such means as the

directing of traffic by traffic management

personnel or discouraging certain traffic

movements by use of traffic cones or barricades.

Traffic management is undertaken to improve

traffic flow on the roadway network.

Traffic management might involve the limited use

of capacity enhancement methods, such as the

provision of an additional lane at a heavily

congested intersection or conversion of a

particular road to one-way traffic. Converting all

the roads leading out of the EPZ to one-way

traffic is not an acceptable alternative because of

the need to provide access for emergency

workers.

Access control is a type of traffic management.

It is necessary to discourage entry into the EPZ

by those who do not belong there. Access control

measures serve to restrict traffic not associated

with an evacuation and keeps it from affecting

the flow of evacuation traffic.

Not all nuclear power plants require detailed

traffic management strategies because traffic

management is implemented only at locations

where it is likely to be effective in reducing

[Locationi I

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Figure L Traffic management diagram.

Roadway Construction

The impact of roadway construction is usually not

considered in developing evacuation time

estimates because disruption due to construction

NUREG/CR-4831 6
is usually temporary and dynamic in nature.

Although roadway construction can greatly affect

capacity of some segments of the roadway

network at certain times, decision-makers must

deal with these effects on a case-by-case basis.

When decision-makers know the sensitivity of the

evacuation network to. changes in demand or

capacity, they can accurately assess the impacts of

a variety of conditions, including construction

activities.

Driver Behavior

It has beeni widely observed that during an

evacuation, drivers tend not to panic, but act in a

manner that promotes good traffic flow (Witzig

and Shillenn 1987). They tend to obey the rules

of the road and act in an orderly manner during

evacuations. Furthermore, it is likely that the*

best driver in the family will be driving during the

evacuation of a family group.

Radial Dispersion

In general, evacuees should move in a direction

radially away from the power plant. Evacuation

routing should not be contrary to the desired

radial dispersion solely for the purpose of more

effectively using available roadway capacity.

However, in some cases it will be necessary, due

to the available roads, for evacuees to move

towards the power plant for some part of their

trip out of the area.

Relocation Centers

A portion of the evacuation traffic will go to preidentified relocation centers. Relocation centers

are located at least 5 miles, and preferably 10

miles, beyond the plume exposure EPZ.

Facilities that serve as relocation centers should

have good traffic circulation in their areas. To

the extent practicable, selection of a particular

facility to serve as a relocation center should not

cause overloading of any portion of the

evacuation network.

Trip Generation Time

For estimating purposes, the population within an

EPZ is usually divided into segments having

similar travel characteristics during an evacuation.

Two major groups are 1) those using personal

autos to evacuate and 2) tho se that require

special transportation. These groups can be

divided further by location and time of day.

"Trip generation time" is the interval between

the issuance (notification) of an order to evacuate

and the beginning of the response, i.e., travel out

of the EPZ. Trip generation time includes the

activity of preparation, and will vary depending

on the location where notification is received by

each evacuee.

Trip generation activities are either independent

(can occur in parallel) or dependent (must occur

in series). For example, a person cannot prepare

to leave home until they arrive home; these are

dependent events. However, the spouse can be*

making preparations to leave while the worker is

returning home; these are independent activities.

The preparation time required by an individual

varies by activity. The time required for the same

activity also varies by individual. It is, therefore,

first necessary to identify the various steps in

preparation time and their sequence. Then, the

distribution of times for the various activities can

be determined, as individuals will each have

different time requirements.

One example of this process is a person at work

who must. return home before beginning

evacuation. The events associated with trip

generation for an individual at work can be

summarized as:

1

2

3

4

5

First notification of public

Individual's awareness of accident

Leave work

Arrive home

Leave home.

7 7 ~NUREG/CR-483 1
However, if the individual was at home (weekend

or night time), the sequence of events is

1

2

5

First notification of public

Individual's awareness of accident

Leave home.

The trip generation time required for individuals

is simply the sum of the times required for each

activity associated with the sequence of events.

The time required for event sequence 1-2 is the

time required for the activity "receive

notification." The time required for event

sequence 2-3 is the time required for the activity "prepare to leave work." The time required for

event sequence 3-4 is the time required for the

activity "travel home." Finally, the time required

for event sequence 4-5 is the time required for

the activity "prepare to leave home."

If everyone had the same time requirements for

each activity, the process of estimating trip

generation would be straightforward. It would be

necessary only to add the times required to

complete each activity. If roadway capacity is not

a limiting factor, simply adding up the maximum

times required for each activity would yield the

time required for the last person (the one taking

the longest time) to beready to leave.

Because different individuals have different time

requirements, the time required by the person

taking the longest time is obviously longer than

that required by many individuals. If the capacity

of the roadway system is the limiting factor,

assuming everyone requires the maximum trip

generation time will result in overestimating the

evacuation time, because some individuals would

have actually left earlier. The use of time

distributions is desirable to avoid overestimating

evacuation time for EPZs where road capacity

affects evacuation time.

To account for the time required by different

individuals to perform an activity, a time

distribution for the activity must be estimated.

The probability distribution for an activity shows

what fraction of the population will complete the

activity in a given span of time. These probability

distributions are constructed in several ways

depending on the data available. Estimating the

distribution from assumed average and extreme

values (minimum and maximum) is a typical

approach. Occasionally, surveys of potential

evacuees can be used to determine the

appropriate distributions.

The various distributions for a given activity must

be combined using compound probability. The

following example illustrates the process.

The example assumes an evacuation at night

from home. The events are: first notification,

awareness of accident, and leaving home. Table

1 shows the warning system effectiveness in

providing notification (activities 1 and 2). Table 2

shows the assumed time required to prepare

(activities 2 to 5). Table 3 is the result of

combining the two distributions.

Combining the distributions, as in Table 3, shows

that the maximum time required, 45 minutes, is

equal to the maximum notification time

(15 minutes in Table 1) plus the maximum

preparation time (30 minutes in Table 2). The

alternative analysis without distributions would

ignore the roadway capacity available before

45 minutes. Without distributions, all evacuees

are assumed to have left home by 45 minutes

after first notification. The use of distributions is

desirable in estimating evacuation times for EPZs

where roadway capacity causes delays to those

evacuating.

Table 1. Notification Distribution

(Activities 1 and 2)

Elapsed Time Cumulative Percent

(Minutes) Notified

5 20

10 60

15 100

NUREG/CR-48318 8
Table 2. Preparation Distribution

(Activities 2 to 5)

Elapsed Time Cumulative Percent

(Minutes) Prepared

5 15

10 30

15 60

20 75

25 90

30 100

Table 3. Trip Generation Time

Elapsed Time Cumulative Percent

(Minutes) Ready

5 0

10 3

15 12

20 30

25 51

30 72

35 86

40 96

45 100

Analysis Tools

The analysis simply involves estimating the

number of vehicles that will evacuate during each

of several time periods and comparing those

numbers (the demand) with the roadway capacity.

The analysis can be done manually when

populations .are small and roadway systems are

not complex. As evacuation demand exceeds the

capacity of -the roadway network, the analysis

becomes more tedious. The use of computer

models can reduce the computational effort and

allows for the consideration and refinement of

more alternatives. However, the use of computer

models requires a competent transportation

analyst. The computer model does not totally

represent reality, and the process of simplifying a

real roadway system into a computer representation can be poorly done. The use of computers

can also give a false sense of accuracy.

The IDYNEV computer model is a public

domain program that is available through the

Federal Emergency Management Agency

(Urbanik et al. 1988a and 1988b). The IDYNEV

model has been successfully used at nuclear

power plants around the United States.

OTHER CONSIDERATIONS IN

EVACUATION TIME ESTIMATE

STUDIES

Besides those issues covered in a transportation

analysis, evacuation time estimate studies often

involve such issues as examining assumptions

about evacuation time, populations dependent on

public transport, special facilities, confirmation of

evacuation, state and local review, reporting of

evacuation results, and updating of evacuation

planning.

Assumptions About Evacuation Time

A number of significant assumptions must be

made in order to estimate an evacuation time for

a particular situation. It may be appropriate to

conduct surveys or collect site-specific data upon

which to base significant assumptions. However,

regardless of the basis, any assumptions used

should be documented. Documenting the

assumptions that went into a particular

evacuation time estimate allows the decisionmaker to better compensate for different

conditions that may exist during an actual

emergency.

Populations Dependent on Public

Transport

Some portion of any population does not own or

have access to an automobile in which to

evacuate. In addition, some members of the

general population have special transportation

.9 .9 NUREG/CR-4831
needs. Those with special needs must be

provided transportation using buses, vans, or

ambulances. Surveys must be conducted in the

EPZ to identify those requiring special

transportation and determine their needs. The

buses, vans, and ambulances required to transport

these people must then be identified.

If enough vehicles exist to transport all those

requiring special transportation in a single trip,

the analysis is relatively straightforward. The only

questions to be answered are 1) the time

required to mobilize the vehicles, 2) the time

required for the vehicles to travel to their

respective assignments, and 3) the time required

to load the vehicles. If the time for these special

evacuation vehicles to be mobilized, driven to the

loading site(s), and loaded is greater than the

evacuation time for the general population, the

evacuation time estimate for this group will be

different from that determined for the general

population.

The analysis is more complicated when multiple

trips are required because of the difficulty in

estimating the outbound speed of special

population evacuation vehicles in evacuation

traffic conditions. In the one-trip scenario, the

special population vehicles cannot be delayed

beyond the time required for the last vehicle to

evacuate the EPZ. In the multiple trip scenario,

the travel speed that is attainable may be limited

by evacuation traffic on portions of the route.

The outbound travel times for buses, vans, or

ambulances must account for delays due to

evacuation traffic.

There are many alternatives in evacuating the

population dependent on public transport. The

final choice will depend on local circumstances

and the preferences of those providing the

service. The critical issues are identifying

* the number of persons requiring

transportation,

* the available vehicles,

* the number of trips required,

* the mobilization time,

* the inbound travel time,

" the route time, and

" the outbound travel time (taking proper

account of traffic conditions).

Special Facility Populations

Special facility populations are similar to the

transport- dependent. The first step is to identify

the location and number of persons at special

facilities. The next step is to determine the

number of vehicles available, the number of trips

required, the mobilization time, the inbound

travel time, the loading time, and the outbound

travel time. If multiple trips or trips to multiple

facilities are required, delays due to evacuation

traffic must be considered. In some cases, certain

special facilities (for example, prisons) have

unique requirements and evacuation planning has

to take into consideration special arrangements

that may be necessary, such as security for the

movement of prisoners.

By definition, special facilities are unique and

addressed on a case-by-case basis in evacuation

planning. The issue is not the identification of

individual evacuation time estimates for these

facilities, but the determination of transportation

needs, the unique requirements at each facility,

and whether special facilities, as a group, will take

longer to evacuate than the general population.

Confirmation Time

Confirmation that the evacuation process is

effective and the public is following the order to

evacuate is to assure that all the population has

been notified. Additional reasons to confirm

public evacuations are to provide assistance to

those having difficulties and to maintain security.

In plume exposure EFZs with a large population,

it is not possible to confirm that everyone is in

compliance in a timely manner. A sampling

approach may be used to determine the

effectiveness of notification systems, or patrols

may be established to pass through the entire

EPZ.

NUREG/CR-4831 110
The sampling approach is to determine the

sample size to generate the desired confidence

that the expected percentage of the population

has evacuated. Statistical analysis can determine

the appropriate sample size to use. A possible

sampling approach is to begin calling randomly

selected households 1 hour before the expected

completion of evacuation. If no one is home at

the expected number of households, notification

is determined to be effective. Otherwise, the

process is repeated after the expected time of

completion of evacuation. Those at home during

the telephone survey can tell the caller if any

.problems exist with notification or if there are

unanticipated problems with transportation. This

sampling approach could be supplemented by

vehicles passing through the EPZ along planned

routes. The use of vehicles could also be the

primary means of confirmation.

State and Local Review

The evacuation planning process is a cooperative

effort of state and local authorities. It is

appropriate that those involved in developing an

evacuation time estimate should obtain input to

and review of the evacuation time estimate study

by state and local officials, including those who

will be involved in implementing traffic

management plans.

Reporting

The evacuation time estimate study documents

the results of a technical analysis of a specific site.

It is important that the results be presented in a

format that makes the emergency response

decision-maker aware of the significance of the

estimates and the underlying assumptions.

The evacuation time estimate study is typically

incorporated into the emergency plan by direct

reference or by citation of key findings. A

summary document may be the most effective

means of presenting study findings to decisionmakers. A summary document could contain

onily that information likely to be used by a

decision-maker, such as time estimates, guidance

on selecting the appropriate evacuation time

estimate, critical variables at evacuation time, and

key assumptions used in estimating evacuation

time. Key issues are how to select an evacuation

time estimate and carry out the proper actions

necessary to achieve the predicted time estimate.

If a summary document is used, a separate

technical report should be prepared to thoroughly

document the study.

The level of documentation provided in the

evacuation time estimate study itself should allow

a competent transportation professional to

replicate the results of the study, albeit at great

effort. Typical reporting formats include

population and vehicle data by evacuation area,

summarized by sectors and distance (2, 5, and 10

miles) from the plant. Alternatively, data may be

provided by geographic areas (i.e., those

emergency planning areas defined in the study).

The roadway network used in the analysis must

be documented, including a map of the

evacuation roadway network. The characteristics

of the roadway network, including road type

(freeway or other type of highway), traffic control

features (traffic signals including type and signal

timing, stop, or yield), and capacity, should be

keyed to the evacuation network map. The data

should be provided in tabular form for manual

analysis or in the form of a computer listing for

computer models.

The features and capabilities of computer models

not in the public domain should also be

documented. The documentation could be in the

form of references to readily available documents

or by providing detailed documentation in

appendices to the evacuation time estimate study.

Traffic management strategies used to reduce

evacuation time should be documented.

Updating

The evacuation time estimate is only as good as

the input data used in the analysis. Changes in

the two key determinants of evacuation time,

population and roadway capacity, must be

11 11 NUREG/CR-4831
regularly monitored and updated. Monitoring of

population growth over time is critical. As a

general rule, a 10 percent increase in population

indicates a need to check evacuation times. An

initial assessment would involve determining

whether growth had taken place in areas

constrained by roadway capacity. If the

possibility exists for increased evacuation times, a

detailed analysis is necessary. A reevaluation

should typically be done every 3 to 5 years. In

areas of little growth, the evaluation would

typically involve verification of the accuracy of the

underlying data and assumptions used in the

analysis.

REFERENCES

Gandhi, P. K. 1972. Effect of Adverse Weather

and Visibility on Capacity of a Signalized

Intersection Approach. M. S. thesis,

Northwestern University, Evanston, Illinois.

Hall, F. L., and D. Barrow. 1988. The Effect of

Weather on the Relationship Between Flow and

Occupancy on Freeways. Presented at the 1988

Transportation Research Board meeting,

Washington, DC.

Jones, E. Roy, and Merrill E. Goolsby. 1969.

Effect of Rain on Freeway Capacity. Texas

Transportation Institute, Research Report 24-23,

College Station, Texas.

Kocmond, W. C., and K. Perchonok. 1970.

Highway Fog. National Cooperative Highway

Research Program Report 95, Highway Research

Board, Washington, DC.

Ries, G. L. 1981. Impact of Weather on Freeway

Capacity. Minnesota Department of

Transportation, St. Paul, Minnesota.

Transportation Research Board. 1985. Highway

Capacity Manual. Special Report 209,

Transportation Research Board, Washington, DC.

Urbanik, T., A. Desrosiers, M. K. Lindell, and C.

R. Schuller. 1980. Analysis of Techniques for

Estimating Evacuation Times for Emergency

Planning Zones. NUREG/CR-1745, U. S.

Nuclear Regulatory Commission, Washington,

DC.

Urbanik II, T., M. P. Moeller, and K. Barnes.

1988a. Benchmark Study of the I-DYNEV

Evacuation Time Estimate Computer Code.

NUREG/CR-4873, U. S. Nuclear Regulatory

Commission, Washington, DC.

Urbanik II, T., M. P. Moeller, and K. Barnes.

1988b. The Sensitivity of Evacuation Time

Estimates to Changes in Input Parameters for the

I-DYNEV Computer Code. NUREG/CR-4874, U.

S. Nuclear Regulatory Commission, Washington,

DC.

U. S. Nuclear Regulatory Commission (NRC).

1978. Planning Basis for the Development of State

and Local Government Radiological Emergency

Response Plans in Support of Light Water Nuclear

Power Plants. NUREG-0396, U. S. Nuclear

Regulatory Commission, Washington, DC.

U. S. Nuclear Regulatory Commission (NRC).

1980a. Criteria for Preparation and Evaluation of

Radiological Emergency Response Plans and

Preparedness in Support of Nuclear Power Plants,

for Interim Use and Comment. NUREG-0654, U.

S. Nuclear Regulatory Commission, Washington,

DC.

U. S. Nuclear Regulatory Commission (NRC).

1980b. Criteria for Preparation and Evaluation of

Radiological Emergency Response Plans and

Preparedness in Support of Nuclear Power Plants.

NUREG-0654, Rev. 1, U.S. Nuclear Regulatory

Commission, Washington, DC.

Witzig, W..F., and J. K. Shillenn. 1987.

Evaluation of Protective Action Risks.

NUREG/CR-4726, U. S. Nuclear Regulatory

Commission, Washington, DC.

NUREG/CR-4831 12
NUREG/CR-4831

PNL-7776

DISTRIBUTION

No. of

Copies

OFFSITE

100 F. Kantor

Emergency Preparedness Branch

Office of Nuclear Reactor Regulation

US Nuclear Regulatory Commission

Washington DC 20555

25 T. H. Urbanik

Texas Transportation Institute

Texas A & M University

College Station TX 77843

1 R. A. Erickson

Emergency Preparedness Branch

Office of Nuclear Reactor Regulation

US Nuclear Regulatory Commission

Washington DC 20555

1- L. H. Cohen

Emergency Preparedness Branch

Office of Nuclear Reactor Regulation

US Nuclear Regulatory Commission

Washington DC 20555

ONSITE

Pacific Northwest Laboratory

J. D. Jamison (10)

D.1

NRC FORM 335 U.S. NUCLEAR REGULATORY COMMISSION 1. REPORT NUMBER

(2-89) (Assigned by NRC. Add Vol., Supp., Rev., NRCM 1102, and Addendum Numbers, if any.)

3201,3202 BIBLIOGRAPHIC DATA SHEET NUREG/CR-4831

(See instructions on the reverse) PNL-7776

2. TITLE AND SUBTITLE

State of the Art in Evacuation Time Estimate Studies for 3. DATE REPORT PUBLISHED

Nuclear Power Plants MONTH YEAR

March 1992 4. FIN OR GRANT NUMBER

FIN 12000

5. AUTHOR(S) 6. TYPE OF REPORT

T. E. Urbanik*, J. D. Jamison Technical

7. PERIOD COVERED 0 tnclusve Date,•

8. PERFORMING ORGANIZATION - NAME AND ADDRESS (IW NRC, provide Division, OfficeorRegion, U.S. Nuclear Regulatory Commission, and mailing address, if contractor, provide.

name and mailing address.]

Pacific Northwest Laboratory

Richland, WA 99352

*Consultant

College Station, TX 77845-9627

9. SPONSORING ORGANIZATION - NAME AND ADDR ESS (If NRC, type "Same as above"; if contractor, provide NRC Division, Office or Region, U.S. Nuclear Regulatory Commission

and mailing address.)

Division of Radiation Protection and Emergency Preparedness

Office of Nuclear Reactor Regulation

U.S. Nuclear Regulatory Commission

Washington, DC 20555

10. SUPPLEMENTARY NOTES

11. ABSTRACT (200 words or less)

In the event of a major accident at a commercial nuclear power station, exposure

of the public to airborne radioactive materials can be prevented or greatly

reduced by evacuating the area immediately surrounding the reactor site. Reactor

licensees are required to conduct studies to estimate the time needed to evacuate

the public from the area surrounding each nuclear power station. The results of

such studies are used by regulatory personnel and emergency planners to assess

the potential effectiveness of protective responses for the public. The time

required to evacuate the public from a 10-mile emergency planning radius is

estimated by analyzing the available transportation facilities and other relevant

conditions within this radius. To support the analysis, data must be collected

and assumptions must be made regarding the transportation facilities, the size

and characteristics of the population and other conditions in the planning zone.

This report describes standard approaches and provides recommendations regarding

the relevant information, assumptions and methods to be used in performing

evacuation time estimate studies.

12. KEY WORDS/DESCR!PTORS (List words orphrases that will assist researchers in locating the report.) 13. AVAILABILITY STATEMENT

Evacuation Time Estimates, ETE, Protective Actions Unlimited

Transportation Analysis, Emergency Planning Evacuation 14. SECURITY CLASSIFICATION

(This Page)

Unclassified

(This R(eport)

Unclassified

15. NUMBER OF PAGES

16. PRICE

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