International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 3

Number 3

September 2009

295

1 INTRODUCTION

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.

296

rial carriers) traveled through the Strait of Istanbul in

2007.

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.

2 MODELING RISK

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