こ う えいフ ォ ー ラ ム 第 27 号 / 2019 . 3

Tools for Risk Estimation and Cost-Benefit Analysis of Road
Geohazard Risk Reduction for Nonseismic and Seismic Events
道路災害の非地震時 ・ 地震時のリスク削減に係るリスク算定と費用 ・ 便益分析ツール
森 幹尋 * ・ 田中 健一 * ・ エミリオ ベントーュラ ** ・ ウィリアム グズマン *** ・アレイダ モントーヤ *** ・ デイマン パストラ *** ・ モニカ ギテレス *** ・アロンソ アルファロ *** ・ ブレンダ カレロ *** ・ へクトール ゴンザレス ***Mikihiro MORI, Kenichi TANAKA, Emilio VENTURA, William GUZMÁN, Aleyda MONTOYA,
Deyman PASTORA, Mónica GUTIÉRREZ, Alonso ALFARO, Brenda CALERO and Hector GONZALEZ

エルサルバドル国への日本国際協力機構 （JICA） 技術支援プロジェクトでは、 道路災害リスク削減に係るリスクと便益の算定と費用 —便益分析を行うツールを開発した。 保全対象は、 被災が懸念される斜面あるいは横断渓流を伴う道路箇所および橋梁である。 このツール開発の目的は、 リスク ・ 対策の便益、 費用— 便益分析結果の提供による道路災害リスク削減への効率的な投資の推進である。 本ツールは、 道路の豪雨時等の非震災と震災を統一的に扱うことを特長としている。 ある道路箇所のリスク （年潜在損失額） と年
被害軽減期待値は、 非震災リスク、 震災リスクについて別々に算定し合算する。 非震災と震災の両者に有効なリスク削減投資は高い投資効率を示し、 投資の推進が期待される。

Keywords ： 道路災害、 リスク削減、 確率論的リスク評価、 地震災害、 費用対効果分析

1. INTRODUCTION（1） FEATURES
The spreadsheet-based Road Geohazard Management
Tool (GeoMT) has been developed through the technicalas destabilization due to slope excavation, deterioration,
and weathering.
A set of worksheets and the manual comprising the
GeoMT is downloadable on the Government of El Salvador
website dacger.mop.gob.sv/.

assistance project funded by the Japan International
Cooperation Agency (JICA) in El Salvador. The outline ofroad geohazards in El Salvador is given in Section 1.3.

（2） PURPOSE
The purpose of developing GeoMT is to promote efﬁcient

The tools measure the risks and the indicators of cost-investments in road geohazard risk reduction based on

benefit analysis of projects for reducing geohazard risks

the risk estimation and indicative cost-benefit analysis

on roads. The tools also analyze the effectiveness of

results. Most of the identiﬁed measures contribute to risk

investments related to reducing seismic and nonseismic

reduction due for both seismic and nonseismic causes.

road geohazard risks. Nonseismic damage is caused not

As for the reduction measures, these comprise slope

only by heavy rain, but also by the loosening of slopes suchprotection, structure and foundation reinforcement,
surface and subsurface drainage works for ground*

コン サルタント 海 外 事 業 本部 環 境 ・ 水資源 事 業 部 地 圏防災 室
Geosphere Engineering & Disaster Management Office,Environment & Water Resources Divisions, International
Consulting Operations** エル サルバドル共和国 公共 事 業 ・ 運 輸 ・ 住宅 ・ 都市開発省 公
共事業担当副大臣 Ministry of Public Works, Transportation,
Housing and Urban Development (MOPTVDU), Vice Minister
for Public Works, the Republic of El Salvador*** エ ル サルバ ド ル 共 和 国 公 共 事 業 ・ 運 輸 ・ 住 宅 ・ 都 市 開 発 省
気候変 動 ・ リスク 管 理 戦 略局 Department of Climate Change
Adaptation and Strategic Risk Management (DACGER),
Ministry of Public Works, Transportation, Housing and Urban
Development (MOPTVDU), the Republic of El Salvador

stability and road geohazard information system. The
effectiveness of the measures is evaluated as the increasein the Safety Degree of Probability (SDP) in years or the
return period for a severe geohazard damage event fora road location. The details are described in Sections 4
and 5.
（3） ROAD GEOHAZARD DAMAGE EVENTS IN EL SALVADOREl Salvador has an area of 21,040 km2. As of December81Tools for Risk Estimation and Cost-Beneﬁt Analysis of Road Geohazard Risk Reduction for Nonseismic and Seismic Events
2016, the total length of the national highway is 6,540 km

refers to a portion of a road that is between 1 andand is 57% paved. The country is in an orogenic zone of

100 km in length; and iii) Peak Ground Acceleration

the Paciﬁc Rim with active seismic and volcanic activities.

(PGA） is the maximum ground surface acceleration

Most parts of the territory are hilly and mountainousof a location unit gal (cm/sec2). PGA can bewith lowlands along the Pacific Coast. In the plateaus

determined by reading the peak acceleration of aand mountains including those in the metropolitan

seismic waveform recorded by a seismograph.

area, valley-like rivers and vulnerable volcanic grounds
predominate. During the May to November rainy season,
many types of geohazards occur such as slope collapse,
fallen trees, rockfalls from mountainside slopes alongroads, road failures due to erosion and collapse ofvalley-side slopes, inundation, flash flooding, and(2) ROAD LOCATIONS TO BE ASSESSEDThe evaluation is performed for every hazardous road or
bridge location.
The classiﬁcation of roads and bridges in a location are
shown in Table 1, Fig.1, and Fig.2:

debris flows. Also, subsidence and sinkholes occur due
to cavitation below the roads. Some of the landslides,

Table 1 Types of Road Locations and Geohazards

road subsidence, and sinkholes occur during the annual

Road Location

Symbolpeak for groundwater level after the rainy season from

Road location withmountainside
slope

M

Fall/collapse and slideRoad location withvalley-side slope

S

Collapse, slide, and ﬂow(road riverside erosion, ﬂood)

Road location withstream crossing

V

Flow (debris ﬂow, earth
ﬂow, ﬂood, and erosion)

Road location with
subsurface storm
drainage-

Subsurface erosion(Sinking due to subsurface
cavitation)

Road location prone
to inundation-

BridgeB

December to January. When earthquakes occur, there
are possibilities of slope collapse, landslides including
the deep-seated and rapid types, rockfalls, and groundliquefaction in the lowlands.
The most efﬁcient plan to reduce road geohazard risks
and prioritize the risk reduction measures can be selectedusing GeoMT.

2. RISK OF ROAD GEOHAZARDS(1) DEFINITION OF GEOHAZARDS
Geohazards are “ events caused b y geological ,geomorphological, and climatic conditions or processes,

Type of Geohazard

Bridge failure due to collapse,
slide and seismic motion
including liquefaction offoundation groundwhich are serious threats to human lives, properties, andthe natural and built environment” (Solheim et al. 2005).
In GeoMT, the types of geohazard risks are categorized
as follows:●

Geohazard material types are classified into rockmass, soil (debris or earth), and water. In most cases,
it is a mixture of materials such as soil and water;●

Geohazard movement is classified into i) fall or
collapse; ii) surface and subsurface erosion; iii)
slide; iv) flow or flood; and v) seismic motion(including ground liquefaction). The movement
types may change or be compounded;●

In GeoMT, i) the term "damage" includes all

Fig.1 Classification of Road Location

damages caused by geohazards such as structuraldeformation and collapse, soil or rockfall, rockThe evaluation of a bridge is divided into four parts:

collapse, and inundation and flood, which affectbridge piers, bridge abutments at origin and destination

roads; ii) "road location" refers to a geographicallysides, and superstructure (Fig.2).

distinguishable location of a road and is normallyless than 1 kilometer in length. A "road section"82こ う えいフ ォ ー ラ ム 第 27 号 / 2019 . 3

Worksheet 1:• Probabilities ofdifferent levels ofroad damages(year)

Worksheet 2:• Potential loss from thedifferent levels of roaddamages (currency)

Worksheet 3:• Potential annual loss (currency/year)• Annual risk reduction benefits (currency/year)
Fig.2 Classification of Bridge Parts

3.	W ORKFLOW FOR ESTIMATING RISK REDUCTION
BENEFITS AND COST-BENEFIT ANALYSIS
Fig.3 shows the workflow for estimating risk, risk
reduction beneﬁts, and cost-beneﬁt analysis for each road

Worksheet 4:• Cost-benefit analysis indicators: benefit-cost
ratio (BCR), net present value (NPV, currency),
economic internal rate of return (EIRR, percent).
Note: Analysis results are generated along the ﬂow indicated by
the arrows.

Fig.3 W orkflow for Estimating Risks, Risk Reduction Benefits,
and Cost-Benefit Analysis

location.
All worksheets in GeoMT are Excel-based as given in
the appendixes. Users can enter data only in the white

The detailed procedures are described in the following
sections of Chapters 4, 5, and 6.

cells. Some of the cells are provided with dropdown lists
to select the appropriate situation for a road location. The
worksheet automatically produces the analysis results.
The list of worksheets comprising GeoMT is shown in

4.	WORKSHEET 1: RATING CHECKLIST FOR PROBABILITIESOF GEOHAZARD DAMAGES
An example of Worksheet 1 is given in Appendix 1.

Table 2.
Table 2 Worksheets in GeoMT
Worksheet No.
Worksheet 1

Output/Location Type
Rating checklist for the probability ofgeohazard damages for a road location
with:-M mountainside slope;-V valley-side slope;-S stream crossing;-BP Bridge piers;-BA Bridge abutment;-BS Bridge superstructure(1) GENERALThis project developed Worksheet 1 (Table 3) and workﬂow(Fig.4) which estimates the Safety Degree of Probability(SDP). SDP indicates the probability of a road damage
event in years due to the probability of road seismic or
non-seismic events. For road locations with subsurface
storm drainage or in an inundation prone area, this is notprepared due to the technical issues involved.
As shown in Fig.4, one of the procedures will estimate

Potential losses due to a road geohazard
event

the SDP for non-seismic events. For seismic events, thePotential annual losses and risk reduction
beneﬁts for a:-SS road location with slope and stream
crossing;-BR bridge.

damages and/or failures, is first estimated. CPGA in gal

Worksheet 2
Worksheet 3

Worksheet 4

Cost-benefit analysis of a geohazard
risk reduction investment for a roadlocation

Critical Peak Ground Acceleration (CPGA) that induces(cm/s2) is then converted to the return period in years,
which is SDP for seismic events. It is noted that SDP isfor both seismic and nonseismic events.
SDP for nonseismic events and CPGA for seismic
events are estimated based on the selected categories in
Worksheet 1 checklist (Table 3). The categories are selectedbased on visual inspection and available information
including geographical information and are used forthe ratings. Simulation, numerical model analysis, andanalysis of historical records can be used to evaluate the
SDP or CPGA of road damage events and those which83

Tools for Risk Estimation and Cost-Beneﬁt Analysis of Road Geohazard Risk Reduction for Nonseismic and Seismic Eventsshould be a priority to the rated SDP or CPGA using
Worksheet 1.
In Fig.4, the design SDP or design Peak GroundAcceleration (PGA) refers to the SDP or PGA that wasused in designing the target of the current structure
before evaluating SDP using GeoMT. In the case of seismic
events, the design SDP is the return period of the design
PGA.
The worksheet rates the SDP in years for nonseismic
events and the critical PGA in gal or cm/s2 for seismic
events simultaneously by selecting the appropriate
categories in Worksheet 1.
(2) DAMAGE LEVELS FOR SDP RATING
Table 4 shows the types of road locations and thedamage levels in the worksheet for rating the SDP of roadgeohazard damages.

Select the applicable categories for checklist
items
for
nonseismic
Rating the SDP bysumming up the
SDP scoresassigned to
selected categories

for seismic
Rating the CPGA bysumming up the PGA
scores assigned to
selected categories

Design PGA ofexisting measures
Design SDP ofexisting measures
Evaluate the SDPof the current
situation by
selecting thelarger values
between the rated
and design SDP
values for existingmeasures

Evaluate the CPGA of thecurrent situation by
selecting the larger
values between rated anddesign values for existingmeasures

Table 3 Structure of Worksheet 1: Rating Checklist for SDP
Rating checklist of
probability in years
Checklist
items

Categories

Items
Select fromwhich may the dropdown
contributelists
to SDP or
PGA

SDP in years
Non-seismic damage
Roadside One-lane Two-lanedamage closure
closureCPGA ofseismic
damage in gal

Scores assigned for selectedcategories

Distress
Select either
items
Yes/No(predictablephenomena
to roaddamages)
Rated SDP in years or
critical PGA

Summing up of the scores assigned to
selected categories

Design SDP No existingin yearsmeasures,of existing design SDP=0
measures
DesignPGA in gal
of existingmeasures

No existingmeasures,design PGA=0

SDP or CPGA of thecurrent situation

Select the larger values between rated
and design for existing measures
Return periodof CPGA ofthe cell justabove

SDP in years of the current
situation for seismic
damageTable 4 Type of Road Location and Damage Levels to be EvaluatedRoad
Location

Damage Level
Non-seismic

Seismic

Road
Three levels For one level of damage:locationof damages:● RoadsideFirst, evaluate CPGA leadingwithto road damage.
mountain damage;● One laneside/
The level of damage against
closure;valleyCPGA is determined from theside slope ● Two laneclosuresite condition.
BridgeThe level of damage: Full-width closure

Evaluate the SDP of thecurrent situation as thereturn period of the CPGAof the current situation

determined for each location along the mountainside andFig.4 Worksheet 1 Workflow: Rating Checklist for SDP

valley-side slopes. SDP is estimated for the two levels

As for nonseismic events such as heavy rain, SDP isof damages: One-lane and two-lane closures. In theworksheet, the function for rating SDP for more than twolanes closure was not included as there are only a few
historical events with which to calibrate the parameters of
the rating function. SDP for three-lanes or more closures
may be calculated by extrapolating SDPs for one-lane andtwo-lane closures.
SDP for road and/or bridges crossing a stream isestimated for flow-type geohazards such as flood and84こ う えいフ ォ ー ラ ム 第 27 号 / 2019 . 3

debris flow. In this case, SDP is estimated only fordamage level defined as “full-width closure.” This isbecause the stream crossing and the bridge are thought
to lead to severe damage requiring full-width closure

Minorcollapse

Valley-side
slope

Mountainside
slope

when exceeding the hydrological limit of the flow rate
(flow volume per second) against the discharge capacityRoadof a watercourse. Full-width closure may occur when thehydraulic limit of the flow speed exceeds the resistance

Inclinedtree

capacity of the bridge structure. Slide type or erosion
type geohazards may also damage a bridge, and once

Inclined
tree
Slope

the bridge is damaged, the damage would be considered

FallenTreesevere similar to full-width closure.
The worksheets rate CPGA which lead to road damage,then evaluate the return period of CPGA for each roadFig.6 Examples of the Item Group: Distresslocation. The worksheet does not include the function for
rating CPGA at different levels of damages because only a
few actual seismic damage cases are available to calibrate

As for nonseismic events, SDP is estimated for eachthe parameters required for the rating. The damage

damage level, and CPGA is estimated for a seismic event.

level of a bridge is judged as full closure when PGA value

SDP and CPGA for each road location are finally rated

exceeds CPGA. As for the location of the stream crossing,as sums of the SDP and CPGA scores allocated to eachthe damage level is evaluated as full road/bridge closure

selected check category. For the SDP of a seismic damage

based on the scenario that an earthquake induces flow-

event, a return period (in years) of the CPGA is calculated

type geohazards that exceeds the discharge capacity of thefor each road location.

watercourse crossing the road.

GeoMT-PGA, an ancillary tool of GeoMT, is forformulating vulnerability curves relating to earthquakes(3) PROCEDURE FOR PROBABILITY RATING
In the worksheets, each check item has two or moreand calculates a set of return periods for specific PGA
values for a location.

choices. For example, in the item "angle of the mountainsideslope up to the point of the inclination change (AS), there
are four choices: "AS ≥ 60°, 60°> AS ≥ 45°, 45°> AS ≥ 30°,
and 30°> AS" （Fig.5） .

(4) CALIBRATION TOOL FOR PROBABILITY RATINGIn GeoMT, the calibration tool was developed to
optimize the scores for SDP and CPGA for each categoryof the rating checklist item. This has been prepared to
improve the accuracy of SDP and CPGA values for a road

Vehicle lane(s)Mountainside
slope

location.
This calibration tool has the following functions:
AS: Angle of themountainsideslope up to thepoint of change ininclination.

●

Create a database of rated and actual SDP and
CPGA values for road locations;●

Allocate the optimum scores of SDP and CPGA to
speciﬁc categories in the checklist items so that theresidual sum of squares of the rated values and theToe of the slope

actual values are minimized based on the database

Fig.5 Angle of the Mountainside Slope

above.
●

Given the versatility of GeoMT, this calibration tool

In the check item group “distress (predictable phenomena

was developed using the “Solver” function, an Excelof road damage) items such as “minor collapse/ fall on the

add-in. This tool can search for optimal predictor

mountainside slope of the road” or “fallen/inclined trees

variable (scores for speciﬁc categories) to determineon the mountainside slope of the road” (Fig.6), the user

the response variable (rated result) calculated by

selects either “Yes or No.”the rating formula.
85

Tools for Risk Estimation and Cost-Beneﬁt Analysis of Road Geohazard Risk Reduction for Nonseismic and Seismic Events(5) ACTUAL SDP FOR NONSEISMIC ROAD DAMAGE
The actual SDP in years for nonseismic geohazards are(6) ACTUAL CPGA FOR SEISMIC ROAD DAMAGE
The actual CPGA values are set up as shown in Table 6.

set up as follows. The actual SDP can be applied to roadlocations with similar conditions as shown in Table 5.
Table 5 Procedure for Setting the Actual SDP
Geohazard
Type

Actual SDP for Non-Seismic Road
DamageMountainside
fall or collapse(1) The return period for rainfall
measured by the rain gauge nearest
to a road location for estimating
historical road geohazard damage
induced by heavy rain
(2) The return period of historical roaddamage events repeatedly occurring
such as fall/collapse of slope at a roadlocation with mountainside slope

Valley-side
collapse orerosion(3) The number of years expected
before each road damage event isestimated by the annual rate of
expansion of slope failure at theroad valley-side.
(4) The return period of hydrologicalevents when the peak f low rates(or speed) of flow-type geohazards(f loods, debris f lows, and others)
exceeds the ﬂow capacity or hydraulicresistance capacity of the stream.

Slide(5) The probability of slide activation
obtained from the following formula
including Factor of Safety (FoS) fora slide type geohazard.
SDP = 500 x (FoS - 1)
where
SDP: Safety Degree of Probability(years)FoS: Factor of Safety

Flow

Same as (4) above

Note for (5): Since there is no standard method for convertingFoS to SDP, the formula was initially proposedin GeoMT. Simply set FoS = 1.2 which is equal to
100 years probability and set FoS = 1 for 0-year
probability which is the situation for balanced
sliding force and resistance force. FoS = 1.2 is thecommon target FoS for slide-type geohazard for
major arterial roads in Japan and cases where slips
occur again higher than measured is very rare. FoS= 1.2 was assumed to be equivalent to 100 years
probability considering that no safety case had been
veriﬁed for more than 100 years after measurement.
The unforeseen cases on the natural conditions fordesign and quality in construction are considered.

86

Table 6 Procedure for Setting the Actual CPGA
Geohazard
Type

Actual CPGA for Seismic Road
DamageMountainside
fall or collapse(1) PGA of historical damage event(2) CPGA estimated from numericalslope hazard analysis

Valley-side
collapse

Same as (1) and (2) above

Slide

Same as (1) and (2) above

Flow

Same as (1) above(3) CPGA estimated from numericalsimulation represents slope fall/collapse/slide into the stream
resulting in ﬂow-type geohazard at
the downstream crossing for a roadlocation.

Seismic
motionincludingliquefaction

Same as (1) above(4) CPGA obtained from the seismic
structural analysis(5) CPGA obtained from the seismicliquefaction analysis

こ う えいフ ォ ー ラ ム 第 27 号 / 2019 . 3(7)	SDP OF A ROAD LOCATION WITH EXISTING MEASURESFOR NON-SEISMIC ROAD DAMAGE(8) C
 PGA OF A ROAD LOCATION WITH EXISTING MEASURESFOR SEISMIC ROAD DAMAGE

SDP rating result can be replaced by the design SDP for

The CPGA rating can be replaced by the design PGA for

existing measures if existing measures function properly

existing measures if existing measures function properly

as shown in Table 7.

as shown in Table 8.

Table 7 Evaluation Procedure for Design SDP
Geohazard
Type

Design SDP for Nonseismic Road Damage

Mountainside (1) Maximum SDP of assumed fall orfall or collapse
collapse event(s) with measuresdesigned for slope stability (e.g.,
removal of the unstable slope, slope
protection) or road protection (e.g.,barrier, shelter)
Valley-side
collapse orerosion

Slide

Flow

(2) The expected number of years for roaddamage occurrence is estimated as theassumed annual rate of expansion ofslope failure with measures designed
at the road valley side.
(3) The hydrological return period forevents with measures designed where
the peak f low rates/f low speed offlow-type geohazards (floods, debris
flows, etc.) exceeds the flow capacity/
hydraulic resistance capacity of thestream(4) The probability of slide activation
obtained from the following formula
including Factor of Safety (FoS) for aslide type geohazard.
SDP = 500 x (FoS - 1)
where
SDP:Safety Degree ofProbability (years)
FoS: Factor of Safety
Same as (3) above

Note: The effects on drainage for surface runoff and vegetation
works on slope stability is not considered in the current
version of GeoMT. There are two reasons: (1) probability ofcollapse/fall or increase in FoS owing to the drainage works
cannot be computed; and (2) Worksheet 1 has checklist items
on slope conditions for spring water, surface water, surface
erosions, and vegetation, therefore, the existing drainage
and vegetation works are reﬂected in the rated SDP.

Table 8 Evaluation Procedure for the Design PGA
Geohazard
Type

Design PGA for seismic road damage

Mountainside (1) CPGA obtained from seismic slope
fall or collapse
stability analysis for the countermeasuretarget slope
Valley-side
collapse

Same as (1) above

Slide

Same as (1) above

Flow(2) Design PGA with the scenario of geomaterials fall /collapse / slide into
the stream resulting in f low-type
geohazard at the downstream crossing
with the road

Seismic
motionincludingliquefaction(3) Design PGA obtained from seismic
structural analysis(4) Design PGA obtained from seismicliquefaction analysis

5.	W ORKSHEET 2: POTENTIAL LOSSES DUE TO A
ROAD GEOHAZARD EVENT (CURRENCY)
An example of Worksheet 2 is given in Appendix 1.
(1) GENERALThe estimate of potential losses due to road geohazards
is conducted for the different level of damage such as
roadside damage, partial-width closure, or full-closure.
The potential economic loss is the sum of the following: 1)
road infrastructure recovery cost; 2) road trafﬁc losses: 3)
human lives lost: 4) vehicle losses; and 5) other losses.
(2) ROAD TRAFFIC LOSSES
A simpliﬁed loss estimation is performed in the case of
the full road closure. The waiting and detour losses are
estimated assuming that either all vehicles decide to wait
for the road reopening or, all vehicles take the shortest
detour road.
The lower value between waiting and detour losses of
all affected vehicles is selected as the road interruption
trafﬁc loss. The estimation uses the value of travel time(currency/hour/vehicle) per vehicle type and unit vehicle
operating cost (VOC) (currency/km/vehicle) per vehicle
type and road condition.
87

Tools for Risk Estimation and Cost-Beneﬁt Analysis of Road Geohazard Risk Reduction for Nonseismic and Seismic Events
In cases of roadside damage or partial-width closure,of the measures (PLA): ARR = PLC – PLA.

traffic losses can be estimated by considering the

The risk reduction target of the design SDP in years

increase in travel time due to reduced speeds or one-or design Peak Ground Acceleration (PGA) should be

way alternating trafﬁc operation. The increase in vehicle

determined by estimating the potential annual losses inoperating costs due to a damaged road is also considered

the case of adopting the planned measures. The procedurein loss estimation.

for setting the design SDP and PGA is the same as shownin Tables 7 and 8.

(3) LOSS OF LIVES AND VEHICLES

Fig.7 shows the risk curves, which are determined by

The rate of lives lost (number of lives lost per totalplotting the annual exceedance probabilities of road damage

affected road user) and the rate of vehicle losses (theevent occurrence (on the vertical axis) and the potential

number of affected vehicles per total vehicle number) is

losses (on the horizontal axis). The potential annual losses

determined by analyzing the actual road damage levels

are indicated as the area between the risk curve and thecaused by each geohazard type.

horizontal axis. The annual risk reduction benefits areindicated as the area between the risk curves for the current

6.	WORKSHEET 3: POTENTIAL ANNUAL LOSS/ANNUALRISK REDUCTION BENEFITS (CURRENCY/YEAR)

situation and the risk curves with the planned measures.

An example of Worksheet 3 is given in Appendix 2.

The potential annual losses is an index of the roadgeohazard risk in GeoMT, which is measured by the
anticipated average losses for a road location in a year.
In Worksheet 3, the current situation refers to thecurrent condition of a road location or section with andwithout countermeasures. Comparison of the risk level
between the current situation and the future conditions
with modified or new countermeasures will be made toevaluate the beneﬁts.
The potential annual losses reﬂect both the probability

Annual Exceedance Probability(%/year)(1) POTENTIAL ANNUAL LOSSES

Annual risk reduction benefits (USD/year) =Potential annual losses for the current situation minus
the Potential annual losses with planned measures forseismic and non-seismic events.
100
10
1
0.1
0.01

0

100

1,000

10,000Potential loss from an event (Currency)

and losses for different levels of geohazard events
for a road location. A road location has different setsof geohazard damage levels (e.g., roadside damage,
partial-width closure, and full-width closure) with theircorresponding probabilities and losses. Estimating risk
as the potential annual loss is determined by integrating
the sets of annual exceedance probabilities (%/year) andlosses (currency) for different levels of road damage events
due to geohazards on a road location. For simplicity,
manipulation of a set of annual exceedance probability
and losses from a road damage event can be used. The
annual exceedance probability is the probability of anevent happening annually (%/year). It is the inverse valueof the Safety Degree of Probability (SDP) in years.
Fig.7 Risk Curve (probability-loss plot)(2) BENEFITS OF ANNUAL RISK REDUCTION
The benefits of annual risk reduction (ARR) is thedifference between the current potential annual losses(PLC) and the potential annual losses after implementation
88

100,000

こ う えいフ ォ ー ラ ム 第 27 号 / 2019 . 3organizations.

7.	W ORKSHEET 4: COST-BENEFIT ANALYSIS FORGEOHAZARD RISK REDUCTION INVESTMENTS
An example of Worksheet 4 is given in Appendix 2.

REFERENCES
1)

The input data required are as follows:●

Technical Consideration Manual for Road Infrastructure in

The investment cost for the geohazard risk
management measure for a road location (currency)●

JICA, COMITRAN, SIECA, 2016: Hydrologic and HydraulicCentral America.

2)

Muzira, Stephen, Martin Humphreys, and Wolfhart Pohl.,

Annual maintenance cost for the installed measure(s)2010: “Geohazard Management in the Transport Sector.”(currency/year)

Transport Notes TRN-40. Report No. 56749, World Bank,●

Discount rate to be used for the cost-beneﬁt analysis

Washington, DC.

●

Annual risk reduction benefits generated by the

Loss Estimation for Road Slope and Pavement, Koei-forum

installed geohazard risk management measure(s)No.17 (in Japanese with English abstract).

*)

(%)

(currency/year): output of Worksheet 4.

3)4)Mori M. et al., 2008: A Study on Simple Potential Annual

Mori M., 2010: Efficient Road Asset Management byUsing the input data described, three indicators ofIntegrated Consideration of Roadway, Bridge and Road Slope,

project worth to support efficient road geohazard risk

Fifth Civil Engineering Conference in the Asian Region andmanagement are calculated as follows:

Australasian Structural Engineering Conference.

●

Net present value (NPV) (currency)●

Beneﬁt-cost ratio (BCR)

Countermeasures for Rainfall-Induced Disasters in El●

Economic internal rate of return (EIRR) (%)

Salvador -Development of a simpliﬁed tool for disaster risk*) Note: The discount rate is input to the calculation of the present
value of benefits and costs considering the social interest
rate as recommended in the Asian Development Bank
(ADB) Guidelines for the Economic Analysis of Projects(1997). The guideline describes that, for decades, theWorld Bank and other international development banks
have used the standard real discount rate ranging from
10-12% to evaluate projects for all sectors and countries.

management-, Paper for INTERPAEVENT International

5)

Mori M. et al., 2014: Risk and Economic Feasibility of

Symposium 2014, in Nara, Japan.
6)

SIECA/CEPREDENAC/SICA, 2010: Manual Centroamericanode Gestión del Riesgo en Puentes (Central America Risk
Management Manual for Bridges).

7)

Solheim, A., R. Bhasin, F. V. D. Blasio, L. H. Blikra, S. Boyle,
A. Braaten, J. Dehls, et al., 2005: “International Centre for

8. CONCLUSIONThe GeoMT updates the database and calibrates it toGeohazards (ICG): Assessment, Prevention, and Mitigationof Geohazards.” Norwegian Journal of Geology 85: 45–62.

improve accuracy in calculating risks and benefits. The
GeoMT has enabled the authors to promote efficientinvestments in road geohazard risk reduction with the useof this tool. The authors propose to disseminate GeoMT
in the Central American region to improve the safety andreliability of managing geohazards for the beneﬁt of roadlogistics for goods and people within the region.
ACKNOWLEDGEMENT ： The authors wish to thank the Japan
International Cooperation Agency (JICA) for the valuable
support and advice, through the Japanese technicalcooperation for the Project for Capacity Developmentof Climate Change Adaptation and Strategic Risk
Management for Strengthening of Public Infrastructure
in El Salvador, Phases I (2012-2015) and II (20162021). Acknowledgment is also given to the persons
involved in the project, to the Ministry of Public Works,
Transportation, Housing and Urban Development(MOPTVDU in Spanish), El Salvador and to other89

Tools for Risk Estimation and Cost-Beneﬁt Analysis of Road Geohazard Risk Reduction for Nonseismic and Seismic Events
Appendix 1: Examples of Worksheet 1: Rating Checklist for Probabilities of Geohazard Damages andWorksheet 2: Potential Loss due to a Road Geohazard Event (currency)

90

こ う えいフ ォ ー ラ ム 第 27 号 / 2019 . 3

Appendix 2: Examples of Worksheet 3: Potential Annual Loss/Annual Risk Reduction Benefit, andWorksheet 4: Cost-Benefit Analysis for a Geohazard Risk Reduction Investment[Worksheet 3-SS] Potential Annual Loss & Risk-Reduction-Benefit for a Location with Slope or Stream-Crossing
white color cell is for user inputs

Location ID

Road Name

Station Origin

GeoMTgray colored cells include instructions or results calculated by this tool

Station Destination

Extension along the road (m)Remarks

Currency US$
Risk Curve

Annual exceedance probability of aroad damage event(%/year)100.00%Nonseismic damage of current situations
Nonseismic damage with planned measures

10.00%

Seismic damage of current situation
1.00%

Seismic damage with planned measures
0.10%

0.01%

1

10

100

1,000

10,000100,000

1,000,000

Total of Nonseismic and seismic damage of current
situation
Total of Nonseismic and seismic damage withplanned measures

Potential losses of a road damage event (US$)

Current
situation/Withplannedmeasures

Items

Unit

Variablesymbols

Potential road damage events for different road damage level
Note: If only one level of damage will be inputted, thesame values shall be inputted for all columns ofdamage level 1, 2, and 3. If two levels of damage will
DamageDamageCalculation be used, the lower level goes on the first column andlevel 1level 2
formula the other value shall be inputted for both columns ofdamage level 2, and 3.
Description of damage level

Same value forcurrent
situation/withplaned measures

Current situation

Nonseismic
DamageWith planned
measures

Lpn Potential economic losses for each damage level obtained using a Worksheet 2.

Potential losses of a road damage event

US$/event

Safety degree of probability of a roaddamage event

years

SDPn_cs Calculated by Worksheet 1-M, 1-V, 1-S or other engineering study

Annual exceedance probability of a roaddamage event%/year

AEPn_cs = 1/SDPn_cs

Potential annual losses of road damage
events in a location

US$/event

ALpn_cs = Integral computation of Lpn and their AEPn_cs

Design safety degree of probability

years

DSDPn

-

Safety degree of probability of a roaddamage event

years

SDPn_pm

If DSDPn > SDCn_cs, SDPn_pm = DSDPn,otherwise SDPn_pm = SDPn_cs

Annual exceedance probability of a roaddamage event in a location%/year

AEPn_pm = 1/SDPn_pm

Potential annual losses of road damage
events in a location

US$/event

ALpn_pm = Integral computation of Lpn and their AEPn_pm

Annual risk reduction benefits of a road location

US$/year

Current situation
Seismic Damage

With planned
measures

Potential economic losses of a road damage
US$/event
event

Partial-width
closure
3

3,000

5

20

200

5.00%

0.50%
131
100

100

100

200

2.00%

1.00%

0.50%
26
105

Lps Loss of damage calculated by using the Worksheet 2

Safety degree of probability of a roaddamage event

years

SDPs_cs Calculated by Worksheet 1-M, 1-V, 1-S or other engineering study

Annual exceedance probability of a roaddamage event%/year

AEPs_cs = 1/SDPs_cs

Potential annual losses of road damage
events in a location

US$/event

ALps_cs = Integral computation of Lps and their AEPs_cs

Design safety degree of probability

years

DSDPs

Safety degree of probability of a roaddamage event

years

SDPs_pm

Annual exceedance probability of a roaddamage event%/year

AEPs_pm = 1/SDPs_pm

Potential annual losses of road damage
events in a location

US$/event

ALps_pm = Integral computation of Lps and their AEPs_pm

e.g. full of 2 lanes road closures

7,000

300
0.33%

If DSDPs > SDCs_cs, SDPs_pm = DSDPs,
otherwise SDPs_pm = SDPs_cs

23
500
500
0.20%
14

Annual risk reduction benefits of a road location

US$/year

Potential annual losses of a road damage eventin a location of current situation

US$/year

ALp_cs = ALpn_cs + ALps_cs

155

US$/yearALp_pm = ALpn_pm_ + ALps_pm

40

Total of Nonseismic andPotential annual losses of a road damage event
Seismic
in a location with planned measures
Damages

Annual risk reduction benefits of a road damage
US$/yearin a location

ARRBs = ALps_cs- ALps_pm

500

Full-width
closure20.00%

ARRBn = ALpn_cs- ALpn_pm

Description of damage levels due to intense earthquake of higher than critical peakground acceleration (PGA)
Same value forcurrent
situation/withplaned measures

Roadsidedamage

Damagelevel 3

ARRB = ALp_cs - ALp_cs

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