599
1
INTRODUCTION
Traditionally,maritime authorities usually makeuse
ofnumberofdeaths,accidents,wrecks,economicloss
etc.asevaluationindexofmarinetrafficsafety.These
aremainlystatisticalanalysisonevaluationfactorsin
thewatersoveraperiodoftime,ofwhichtheresults
are static, and lack of real‐time, process
control and
management.It is unable to reflect the safety
situationinreal‐time.Tobeabletodirectlyreflectthe
real‐timedegreeofsafetyinwaters,weestablisheda
complete maritime vessel traffic safety evaluation
indexsystem,andquantifiedtheresultsofthesafety
evaluationinnavigablewaters.
itiscrucialtoprovide
intuitivereal‐timeevaluationresultsformarinesafety
personnel.
With the rapid development of information
technology, the major shipping countriesin the
world gradually established a more complete shore‐
based AIS networks for busy waters, which can
monitor marine traffic conditions in real‐time, and
acquire
avarietyofsafetydataaffectingmarinetraffic
suchasships’movement,weatherconditionsandso
on.Thesereal‐timedataprovideabasicguaranteefor
marine traffic safety index. Lots of researches on
marine navigation safety have been conducted by
many scholars and marine safety study is shifted
gradually
aswell fromstatic to dynamic analysisof
real‐time processing research. Currently, in the
relative field of marine navigation safety, in the
paper[1], the author put forward the concept of a
tentative real‐time safety index, established a real‐
time safety evaluation index system, and more
considerations of the environmental
impacts on
navigation safety were given, including some
relatively fixed, rarely changing factors, but the
dynamic nature of the evaluation results is not so
strong. In the paper [2], the author analysed
navigation safety factors, and utilized a fuzzy and
comprehensive evaluation method to build a more
complete navigation environment
safety evaluation
indexsystem,andselectagroupofexperimentaldata
to demonstrate its feasibility. However, not all
Marine Traffic Real-Time Safety Index
T.Xu,Q.Y.Hu,Z.Xiang&D.L.Wang
ShanghaiMaritimeUniversity,Shanghai,China
ABSTRACT:Toreflectthesafetydegreeofmarinetrafficinreal‐timeandintuitively,thispaperputforwarda
conceptofreal‐timesafetyindexofmarinetraffic,establishedmarinetrafficreal‐timesafetyindexsystem,and
constructedareal‐timesafetyindexevaluationmodelbyusingvesseltrafficandnavigation
environmentaldata
providedbyshore‐basedAISbasestationnetwork,andquantifyingavarietyofdatawhichimpactsthesafety
ofmarinetrafficsuchasships’real‐timedynamicdata,weatherchangesandsoon.Acontinuousreal‐time
evaluation to a specific area was carried out in the form
of real‐time index curve, taking the Waigaoqiao
ChannelofPortShanghaiasanexample,toverifythefeasibilityandeffectivenessofmarinetrafficreal‐time
safetyindex.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 8
Number 4
December 2014
DOI:10.12716/1001.08.04.16
600
indicatorsselectedhadthecharacteristicsofreal‐time
changes and the required data was obtained with
greatdifficulty.
The concept ofmarine traffic real‐time safety
Index(abbreviatedas
MTRSI)proposedinthispaper
is a dynamic safety value that through the
establishmentofnavigationalsafetyevaluationindex
system,quantifyrelativeparametersaffectingmarine
navigation safety, evaluate the situation by using
relative safety evaluation method, and display the
evaluationresultsinformofindex.
To achieve MTRSI
, three basic steps shall be
followed:
1
Establishdifferentevaluationindexsystemasper
differentneeds;
2
Choosedifferentsafety evaluationmethodsasper
evaluationpurpose;
3
Displayevaluationresultsintheformofindexand
publishthroughInternet,atthemeantime,publish
throughinternetthereal‐timeinformationofeach
indextofacilitatetheinquiryanddecision.
2
MODELOFMTRSI
MTRSI is a real‐time index that reflects real‐time
safetyconditioninspecificwaters,whichisacomplex
modelandofwhichmanyfactorsareverydifficultto
be described using traditional mathematical models.
Thus,accordingtothe principlesofevaluated object
features and evaluation methods, comprehensive
scoring method is selected as final calculation.
AlgorithmprocessisshowninFig.1.
Figure1.Marinetrafficreal‐timesafetyindexdatamodel
Theselectionofcomprehensivescoringmethodis
mainlybasedonthefollowingfourpoints:
1
Determine the appropriate index of real‐time
evaluation model according to investigation and
expertadvice;
2
Fordeterminingthevalueofeachindex,selectthe
appropriate method of calculating the value of
quantitativeindex;
3
Consider using a weighted sum score for each
safetyindexcontributiondifferences;
4
Usecomprehensivescoringmethodtodisplaythe
evaluationresultsinvalue.
3 ESTABLISHMENTOFSAFETYEVALUATION
INDEX
MTRSIvariesovertimeintheevaluationofthemodel
system. The evaluation index is not the more the
better, the key lies in the contribution of evaluation
results.
3.1
selectevaluationindex
Many factors affect marine traffic safety. They are
divided into relatively static factors such as channel
facilities in a certain period, anchorages, berths and
otherfactorsetc.,andreal‐timedynamicfactors,such
as collision between ships, natural conditions,
visibility etc. In this article, we preferred to choose
thoseindexesthat
mayoccurinreal‐timeandshort‐
termasanevaluationindex.
We select indexes as few as possible to reflect
objectively the marine navigation safety. Through
consultation with specialists and field investigation,
weanalysedandsummarizedtheprimekeyindexes
that changes may occur in real‐time and short‐
term,
andeventuallyestablishedtheeffectsofmarinetraffic
inreal‐timesafetyindexwhichare4primaryindexes
and5secondaryindexes.Marinetrafficsafetyindexes
affecting marine real‐time safety are mentioned in
Table2.
Table2.Marinetrafficreal‐timesafetyindexanalysis
_______________________________________________
PrimaryindexSecondaryindex
_______________________________________________
Shiptrafficconditions Shipsdifference
Shipsencounterrate
_______________________________________________
NaturalEnvironment Leewayanddriftangle
Visibility
Diurnalvariation
_______________________________________________
EmergenciesCollision,grounding,
outofControletc
_______________________________________________
DangerouscargoshipsChemicalTanker,LNG,LPGetc
_______________________________________________
3.2
Obtainandcalculateindexweights
Toobtainindex weight, firstly designthe
questionnaire according to classification and
requirements,andthenuseAHPmethodtoconstitute
judgmentmatrixaccordingtothequestionnaire.Each
indexweightiscalculatedbyjudgmentmatrix.Dothe
aboveprocesstoallquestionnairesandcalculatethe
index weight vector that all experts assigned,
and
then after the weight vector anomaly detection ,
average all detection passed weight vectors ,and
finally obtain the weight of each index values as is
showninTable3.
MTRSI
Indexweights
CalculationModule
EvaluationIndexSystem
comprehensivescoring
ThevalueofmarinetrafficReal‐
timesafet
y
Index
Quantifyingand
standardizingtheindex
module
601
Table3.Indexweightvalues
_______________________________________________
IndexCode indexnameWeightValues(
i
w
)
_______________________________________________
Index1 Shiptrafficcondition0.3315
Index2 NaturalEnvironment0.3013
Index3 Emergencies0.1894
Index4 Dangerouscargoships0.1778
Index5 Shipsdifference0.2601
Index6 Shipsencounterrate0.7399
Index7 LeewayandDriftangle 0.2993
Index8 Visibility0.3996
Index9 Diurnalvariation0.3011
_______________________________________________
4
ANALYSISOFMTRSI
Selecting appropriate index calculation can grasp
index changing trend intuitively and clearly. Once
MTRSI
abnormally changes, the reason can be
analysedthroughthechangesofMTRSI.
4.1
Differenceofships
Difference of ships means manoeuvrability is
differentbetweenvesselsofdifferentscale,andtime
requirementofactiontoavoidcollisionisdifferentas
well.Generally,navigationalofficersonlargevessels
navigatevesselsincomplywith relativeregulations,
while navigational officers on small vessels tend to
navigateatrandom.Trafficenvironmentin
fairways
will be very complex, and risk ship collision will
increase. The mean square difference (m) of ship’s
length as the value of ship’s difference can be
calculatedbyformula(1):
n
i
i
L
n
L
1
1

n
i
i
LL
n
m
1
2
)(
1
(1)
4.2
Shipsencounterrate
Inthispaper,wetakeuseoftheGoodwin’stheoryof
Ship Safety Domain and calculation ofShips
encounter rate in paper[3].Considering not only the
current time the ship will encounter state, but also
taking into account the situation of the ships
encounterinthefurthertime.Whenothershipenters
the field of my own ship safe domain , recorded as
one. Taking into account real‐time capability of the
MTRSIwillbeselected everyfive minutesasa time
unit, collected ship data for few minutes as
experimentalbase data. Setevery five minutes for a
time unit and
denoted as 0,1,...,n, etc., and then
averageeverytimeunit,denotedeveryfive minutes
foratimeunit,regardas0,1,...,5.Accordingtothe
abovedata,calculatetheshipwillencounterrate(M):
）（
）（
S
E
M
riskencounter ship of time
TCPA
(2)
i
iiiiii
aaaaaaE
543210
6
1
6
2
6
3
6
4
6
5
*1
(3)
Whereinformula3,
ij
a representsthenumberof
ships encounter in the no. j time point of no. i time
unitunitsthatisexpectedtooccur.
S Totalnumberofvesselswithineveryminute (4)
4.3
Leewayanddriftangle
Leewayanddriftangleiscalculatedbyaveragingthe
differences between COG and HEADING of all
vesselsinspecificnavigablewaters.
4.4
Visibility
According to the relevant navigation regulations,
whenvisibilityislessthanaspecificvalueinnarrow
channels or in waters with heavy traffic, ship traffic
controlwould beimplemented or channel wouldbe
closed. In good visibility, officers on watch have a
clear and wide vision, and it is easier for
them to
make correct decisions to navigate the ship more
safely.
Table4.Indexcalculationsystem(indexvalueiswithintherangeofinterpolationprocess)
__________________________________________________________________________________________________
PrimaryindexSecondaryindexSummary
__________________________________________________________________________________________________
Shiptrafficconditions ShipsdifferenceMeansquareerrorofLengthoftheship(calculatedaccordingto
Index1Index5existinghistoricalstatistics,todeterminetheminimumlengthofthe
shiparethevarianceis32andthe maximumis92)
___________________________________________________________________________
Shipsencounterrate AccordingtoGoodwin’sTheoryinpaper[2],shipencounterrate
Index6calculationmethodtochooseadesignedwatersbasedonhistorical
data,theshipencounterratewithin[0.02,0.4]interval.
__________________________________________________________________________________________________
NaturalEnvironment LeewayandDrift angle Accordingtocourseofadvanceandheadingdifference.The
Index2Index7minimumvalueis0°,themaximumvalueis14°.
___________________________________________________________________________
VisibilityMorethan10kmdefinesas1,lessthan500mdefinesaszero.
Index8
___________________________________________________________________________
DiurnalvariationTimeisbetween0800and1800(daytime)thevalueis1,andthe
Index9remainingtime(night)is0.7,thisindexisnotinterpolated.
__________________________________________________________________________________________________
EmergenciesCollision,grounding, Noincidentstheindexvalueisone,moretwosuddeneventsiszero.
Index3outofControl
__________________________________________________________________________________________________
DangerouscargoshipsChemicalTanker, Nodangerousshipisone,therearethreeormoredangerousshipsis
Index4LNG,LPGzero.
__________________________________________________________________________________________________
602
4.5
Diurnalvariation
Itismoredangeroustonavigatetheshipinnighttime
compared with day time, due to dark light and
interferenceofthebackgroundlightsfromlandalong
the fairway, thus increasing difficulties of judgment
of collision avoidance. Meanwhile, OOW is easy to
fatigueatnight,especiallyinthetwilighthours
which
isaccident‐pronetime,mostpeoplefeelfatigue,and
visionblurred.
4.6
Emergencies
Dataofemergenciesimpactingnavigationalcondition
can be grasped according to emergencies, distress
alert from fault vessel, navigational warnings and
other information. When grounding, collision, and
out of control and other emergencies occur in
navigable waters, navigation conditions will change
dramatically, prompt appropriate action shall be
taken to prevent the situation
from further
deterioration.
4.7
Dangerouscargoships
The presence of dangerous cargo ships can cause a
restrictiontovessels’actiontoavoidcollisioninentire
navigablewaters,andaneffectonnavigationorderto
somedegree.Andtheoverallshippingorderwillbe
affected.
In summary, scope of each index is determined
through expert consultation, questionnaires, as well
astheprocessingandanalysisofhistoricaldata.The
indexes related to water safety in real time, will be
carried out within the value normalized to [0,
1].Calculation of the values of indexes is shown in
Table4.
Through analysing real‐time indexes affecting
marinetrafficsafety,combinedwiththe
aboveindex
values and weights, safety index values can be
obtained by calculation in every one minute. Index
value to determine marine traffic in real‐time is
calculatedasfollowing:

100651
65
wIndexwIndexIndex

789
Index2 Index7 w Index8 w Index9 w 100
(6)
MTRSIcalculationformulaisasfollowing:

12
34
MTRSI Index1 w Index 2 w
Index3 w Index4 w 100


5
EXPERIMENT
InordertoverifythesuitabilityofMTRSImodel,the
‘Waigaoqiao’ channel between ‘Yuanyuansha’
precautionary area to ‘Wusongkou’ precautionary
area in Shanghai port were selected for this
experiment.
5.1
ExamplesofMTRSI
The analysis was based on data from 1131LT to
1200LT on 27
th
, April, 2012. Each initial index value
andthenormalizedvalueareshowninTable5:
Table5.Initialindexvalueandnormalizedvalue(2012‐4‐27
11:31)
_______________________________________________
values Initialindex Normalizedindex
indexvaluevalue
_______________________________________________
Shipsdifference 39.382463 0.877
Shipsencounterrate 0.2918 0.2857
LeewayandDriftangle 0.081481 0.98836
Visibility101
Diurnalvariation11
Emergencies01
Dangerouscargoships01
_______________________________________________
MTRSI calculated result is 81.31 at 11:31 in
comprehensive score method , and so on, MTRSI is
calculated between 11:31 and 12:00 per minute,
MTRSI exponential curve and the primary index
valuesareshowninFigure2,allvaluesarebetween0
and100.
marine traffic real-time index
0
20
40
60
80
100
11:31
11:33
11:35
11:37
11:39
11:41
11:43
11:45
11:47
11:49
11:51
11:53
11:55
11:57
11:59
time
Emergencies Dangerous cargo ships
ship traffic condition Natural Environment
marine real-time safety index
Figure2.MTRSIandprimaryindexvaluescurve
In Figure 2, not only real‐time fluctuations in
MTRSIcan be found, but also the indexfactors that
mainly changed in this model, such as ship traffic
conditionsetc.
5.2
MTRSIdisplaying
Make use of calculation result of MTRSI model ,
demonstrateMTRSIwithinaparticulartimebyXml,
MySqlandFlextechnologyinFig3.Theredareain
Figure3isanareaofhighriskofcollision,thevalue
intheformindexisthecurrentMTRSI.
Figure3.MTRSIdisplayingprocedureinterface
603
6
CONCLUSIONS
MTRSI can reflect directly marine traffic safety
situation in port waters and the key channel in real
time,atthesametimeitcanbeusednotonlyasport
safetyproduced reference, but also asa reference of
marine traffic safety supervision. According to high
risk area or high
risk periods of marine traffic
recognized by MTRSI model, marine authorities can
increase marine enforcement forces and carry out
trafficguidanceandcontroltimely.Inaddition,itcan
help shipping companies, port services and pre‐
arrival ships to keep abreast ofport congestion
andsafety conditionsin time so that
they can make
appropriatearrangement.
By tracking long‐term MTRSI trend, we can
analysethechangingtrendand regularity ofmarine
traffic safety in port waters and key channel, and
MTRSI can be used to evaluate the effect of new
marinesafetymanagementmeasuresetc.
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[2]E.M.Goodwin. A statistical study of ship domain. The
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