International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 3
Number 3
September 2009
The Turkish Straits (the Straits of Istanbul and
Canakkale), which have narrow and winding shapes
that give them the semblance of a river, are one of
the most strategically important waterway systems
in the world. As the Black Sea's sole maritime link
to the Mediterranean and the open seas beyond, they
are a vital passageway not just for trade but for the
projection of military and political power. Also, their
hard to navigate geographical properties, meteoro-
logical conditions, dense and increasing transit/local
traffic, vessel/cargo characteristics, and physical
hindrances, such as cross continental bridges, energy
transfer lines, make the Straits’ traffic conditions
quite complex and risky. Moreover, this narrow pas-
sage runs through the heart of Istanbul, home to over
12 million people and some of the world’s most cel-
ebrated cultural and historical heritage.
Geographically, the Strait of Istanbul is one of the
narrowest waterways in the world. It has length of
31 kilometers with an average depth of 45 meters
(Ozturk, 1995). Its average width is 1.5 km, where
this width decreases to 700 meters at its narrowest
point (Tan & Otay, 1999). Additionally, frequent
adverse meteorological conditions, such as dense
fogs and high currents and winds, contribute to the
complexity of navigation in the Strait.
There are also some non-natural factors making
navigation through the Strait of Istanbul hazardous.
One of them is the dense local traffic, such as intra-
city passenger boats, fast ferries, fishing boats,
pleasure boats, tugboats etc. (VTS User Guide,
2004). Another important non-natural factor that
negatively effects navigation in the Strait is the fre-
quency and cargo characteristics of transit vessels.
Over 56,600 vessels (10,050 being dangerous mate-
Simulation-Based Risk Analysis of Maritime
Transit Traffic in the Strait of Istanbul
B. Ozbas & I. Or
Bogazici University, Istanbul, Turkey
O. S. Uluscu & T. Altıok
Rutgers, The State University of New Jersey, NJ, U.S.A.
ABSTRACT: In this manuscript, development and preliminary results of a simulation based risk modeling
study for the Strait of Istanbul is presented. The goal of this research is to analyze the risks involved in the
transit vessel traffic in the Strait of Istanbul. In the first step of the study, the transit vessel traffic system in
the Strait of Istanbul has been investigated and a simulation model has been developed. The model gives due
consideration to current traffic rules and regulations, transit vessel profiles and schedules, pilotage and tug-
boat services, local traffic, meteorological and geographical conditions.
Regarding risk assessment, two sets of factors are used to evaluate the risk of accident in the Strait: the proba-
bility of an accident and its potential consequences, as estimated and evaluated at various points along the
Strait. Experience has shown that maritime accident occurrences can be very dissimilar from one another and
therefore, probabilistic analysis of accidents should not be done independent of the factors affecting them.
Thus, in this study, we have focused on the conditional probability of an accident, under a given setting of
various accident causing factors. Unfortunately, historical accident data is by far insufficient for a proper sta-
tistical consideration of all possible settings of these factors. Therefore, subject-expert opinion is relied upon
in estimating these conditional accident probabilities. Assessment of the consequences of a given accident (in
terms of its effects on human life, traffic efficiency, property and environment) was also accomplished using a
similar approach.
Finally, by integrating these assessments into the developed simulation model, the risks observed by each
vessel at each risk slice are calculated in regard to the natural and man-made conditions surrounding. A sce-
nario analysis is performed to evaluate the characteristics of the accident risk as the vessel moves along the
Strait. This analysis allows us to investigate how various factors impact risk. These factors include vessel ar-
rival rates, scheduling policies, pilotage service, overtaking and pursuit rules, and local traffic density. Policy
indications are made based on the results of these scenarios.
rial carriers) traveled through the Strait of Istanbul in
In order to control and mitigate maritime accident
risks and improve the safety of navigation in the de-
scribed dire environment, The Bureau of Turkish
Strait’s Maritime Traffic Services (BMTS) has set
up a sophisticated Vessel Traffic Control & Moni-
toring System (VTS), (covering not only the Strait,
but also 20 miles into the Black Sea and the Sea of
Marmara) and has established and effected a set of
stringent Maritime Traffic Rules and Regulations
(R&R). The vessels arriving at the northern and
southern entrances of the Strait of Istanbul enter and
then navigate through the Strait according to the di-
rections of the BMTS, which are based on the VTS
inputs and the R&R (VTS User Guide, 2004).
Figure 1. The Strait of Istanbul
The objective of this study is to analyze the risks
involved in the transit vessel traffic in the Strait of
Istanbul. In order to achieve this, a detailed mathe-
matical risk analysis model is developed to be used
in a risk mitigation process (Uluscu et al., 2008).
Firstly, in order to study and better understand the
system, a functional simulation model of the transit
vessel traffic in the Strait of Istanbul is built. In this
simulation, which is based on the mentioned R&R,
in addition to the geographical/meteorological con-
ditions, transit and local vessel traffic in the Strait,
the current vessel scheduling practices are also mod-
eled using a specially designed scheduling algo-
rithm. This scheduling algorithm, which is devel-
oped through discussions with the BMTS
authorities, primarily mimics their decisions on se-
quencing vessel entrances, as well as northbound
and southbound traffic flow time windows (Uluscu
et al., 2009). Finally, by integrating, expert opinion
and historic data based risk assessments into the de-
veloped simulation model, the risks generated by
each vessel, are calculated in regard to the natural
and man-made conditions surrounding it (such as,
vessel characteristics, pilot/tugboat deployment,
proximity of other vessels, current & visibility con-
ditions, location in the Strait etc.), as the vessel
moves along the Strait. Preliminary results obtained
in the application of this procedure are presented and
discussed in later sections.
The primary objective of this study is to develop a
realistic model to assess and investigate maritime
risk imposed by the transit traffic in the Istanbul
Strait; furthermore, it is expected that such a model
and an accompanying scenario analysis will suggest
and support strategies and operational policies that
will mitigate the risk of maritime accidents that will
endanger the environment, the inhabitants of Istan-
bul and impact the economy, while maintaining an
acceptable level of vessel throughput.
Regarding the modeling of risk, first events that
may trigger an accident are identified and defined as
instigators (for example, there can be a mechanical
failure in the vessel or the captain can make a judg-
mental error, during the transit of the vessel through
the Strait of Istanbul). Through the examination of
the historical accident data and discussions with lo-
cal maritime experts, the occurrences of the follow-
ing incidents have been identified as possible insti-
gators of maritime accidents in the Strait: human
error, rudder failure, propulsion failure, communica-
tion and/or navigation equipment failure, and other
mechanical and/or electrical failure. Clearly, the oc-
currence of an instigator depends on the situation,
which may be represented by a vector of situational
attributes. Given the occurrence of an instigator, typ-
ical accidents that may occur in the Strait have been
considered and classified as, collision, grounding,
ramming, sinking and fire and/or explosion. It is also
possible to have accidents may occurring in chain,
so that a prior (1
tier) accident may cause later (2
tier) one. 1
tier accident types include collision,
grounding, ramming and fire and/or explosion, while
the 2
tier accident types include grounding, ram-
ming, fire and/or explosion, and sinking. Potential
consequences of the 1
and 2
tier accidents include
human casualty, property and/or infrastructure dam-
age, environmental damage and loss of traffic effec-
tiveness and throughput. This framework is present-
ed in Figure 2. Defining situations (factors and their
states) that affect the likelihood and/or impact level
of instigators and accidents is critical for the intend-
ed risk analysis. Such factors as called Situational
Attributes, and are divided into two groups: attrib-
utes influencing accident occurrence (vessel class,
vessel reliability, pilot request, tugboat request, visi-
bility, current, local traffic density, vessel proximity,
zone and time of the day) and attributes influencing
consequences (vessel cargo, length, zone). These