Maritime Traffic STRATEGIES International Transportation (67) 2 | 2015 13 Traffic flow at the entrance to-the Baltic Sea The Kadet Trench: maritime traffic flow and its parameters Vessel movements, traffic flow, traffic volume, congestion Navigation in the Baltic Sea is challenging, mainly because of its relative shallowness, the ice cover in wintertime and the narrow navigation routes. The present paper focuses specifically on the Kadet Trench (KDT), which provides the only deep-water access to the Eastern Baltic. The trends in ship sizes and speeds in the Kadet Trench are monitored through the collection and evaluation of AIS data for the years 2009 to 2014. Moreover, the paper offers an analysis of the composition of the traffic flow and the hourly and weekly fluctuations of traffic density. Authors: Nina Vojdani, Manfred Ahn, Frank Hartmann, Carsten Hilgenfeld I n 2012, around 9.1 % of total volume of international seaborne cargo was handled in the ports bordering the Baltic Sea [1, 2]. The Kadet Trench (KDT) represents the only deep-water entrance to the Eastern Baltic (see figure 1). The other entrance to the Eastern Baltic, i.e. the Öresund strait between Denmark-Copenhagen and Sweden-Malmö, is limited to a navigable draft of 8 m. There are further smaller belts and sounds in Denmark that remain non-navigable for merchant shipping due to their insufficient draft [3]. Thus the Kadet Trench with its navigable draft of 16 m and its geographical proximity to the German Baltic Sea as well as to the Kiel Canal (North Sea - Baltic Sea) is primarily used by ferries, tankers and feeder vessels in order to call at diverse ports along the Baltic Sea. The transport volume in the Baltic Sea is expected to grow in the future. The Kadet Trench The research area includes the KDT, where traffic is controlled by the Traffic Separation Scheme (TSS) “South of Gedser.” The west side is geologically limited by the Danish Falster Island and its extensions of the Gedser Reef. The inshore traffic zone “Fischland” was established in 2007, to the south and east of the TSS. Figure 2 shows the ship trajectories within the KDT: Paths used only once are represented in white. The more often a trajectory has been used, the darker the color. This color scheme makes the main shipping routes of the TSS visible. At the same time, a number of shipping trajectories that are not part of the TSS traffic flow are revealed. For the analysis, the research area is projected in a square format, with buoy W 71 of the Gedser Reef as the most south-western point and buoy E 72, marking the inshore traffic zone, as the most north-eastern point. This area is divided by the buoys 71 and 72, whose distance is 3.66 sm or 6.78 km from Figure 1: Entrance to the Eastern Baltic Sea Source: openseamap Figure 2: Ship movements in the KDT Source: Trajectory data overlay on electronic sea chart STRATEGIES Maritime Traffic International Transportation (67) 2 | 2015 14 each other (see figure 3). On the west side, ships navigate southwards, and on the east side, ships sail northwards. Both shipping directions are additionally subdivided into shallow-water (outside) and deep-water areas (inside). According to an IMO recommendation, ships with a draft of more than 13 m should take into consideration additional security measures such as taking a pilot on board for this passage [4]. Data basis The analysis is based on Automatic Identification System (AIS) data supplied by the Federal Waterways and Shipping Directorate (WSV). The AIS is a broadcast radio method, based on the ITU recommendation ITU-R M.1371-5, for the transfer of codified information [5]. The standard was confirmed by the International Maritime Organisation (IMO) in the year 2000 and the AIS regulation was integrated in the International Convention Safety of Life at Sea (SOLAS). The method offers detailed information on ships as well as their cargo in order to allow onshore traffic control by the respective coastal state, and thus aims primarily at avoiding ship collisions and increasing security at sea. The data were obtained via the official channels from the WSV, which functions as the official directorate since 2011 [6]. The data base excerpt shows a special data editing format so that it had to be converted in a first step. For a more extended overview of the situation, the available time frame from 03/ 2010 to 12/ 2014 of the WSV data base was complemented by earlier AIS data covering the time span from 01/ 2009 to 2/ 2010 obtained from the Department of Maritime Studies at the University of Applied Sciences Wismar. The low net coverage resulted in a low quality of the data, especially with regard to the northern part of the Kadet Trench, so that the data from 01/ 2009 to 02/ 2010 by themselves were inadequate for a full representation of the overview of the situation. Consequently, these data were only used to provide information of speed and dimensions of the ships. Evaluated data For the preparation of the analysis, the AIS data were filtered and stored in a suitable project data base. This data base contains the static and dynamic information of all ships that belonged to the traffic flow of the KDT. The data on vessels that were present in the concerned sea area but were not part of the traffic flow were deleted. This included for instance those ships present in the KDT that only crossed the TSS, fished in the TSS or simply touched the TSS [7]. The primary aim was to create a data base containing all relevant vessel data in order to enable an analysis of all vessels that were located in the area and followed the traffic route. Traffic volume The analysis of the resulting project database revealed that the number of vessels in the KDT slightly decreased over the years studied, i.e. from 03/ 2012 to 12/ 2014 (see figure 4). The period from 01/ 2009 to 02/ 2010 was excluded from the investigation of the traffic volume since - as mentioned earlier - the low AIS net coverage of the data source did not cover all ships and thus failed to identify all passages. Estimated seasonal variations are only marginal and can be ignored. However, it has to be noted that every year, the traffic volumes show a dip at Christmas and return to the previous level with the turn of the year. The data of the years 2010-2014 document a total of 50,000 vessel movements, which contradicts reports on the matter [8 - 13] listing 65,000 to 85,000 vessel movements. Even if counting also those ships that moved in the complete sea area between the coastal lines but were not part of the traffic flow (ca. 2,500 p.a.) and including private ships (ca. 5,000 p.a.), the number of ship movements between the German and Danish coasts would amount to 57,500 at the most. Traffic speed During the observation period from 03/ 2010 to 12/ 2014, the average ship speed of the traffic flow was analyzed for a period of 20 days (see figure 4). The annual average of vessel speed remains relatively constant at 12.5 to 13.5 kn (1 kn = 1 sm/ h ≈ 1.852 km/ h). The only significant reduction of speed can be observed precisely at Christmas. Throughout the six years investigated, a slight reduction of the average speed can be observed. Whereas in 2010 the average speed was 13.5 kn, the speed in 2014 was 13.1 kn. Thus, from 2010 to 2014, slow steaming for the area of the Kadet Trench can only be traced at a very low level. For the evaluation of figure 5: The ship‘s bridge team usually opts for a speed between 5 and 15 kn. The ships reported to travel at speeds beyond 20 kn as well as below 4 kn Figure 3: Core area of the KDT Figure 4: Traffic volume and traffic speed 03/ 2010 to 12/ 2014 Maritime Traffic STRATEGIES International Transportation (67) 2 | 2015 15 are very few. 99.8 % of all ships travel at an average speed of 24 kn or less. Traffic speed beyond 25 kn was only chosen by class A ships (see figure 6). Ship sizes and width The 50-days average value curve in figure 7 shows the development of ship length and width, confirming the general trend of increasing ship sizes. As expected, the ships‘ length increases proportionally to the ships‘ width. In 2014, the average ship in the KDT measured around 150 m in length and 22.5- m in width (values measured at the ship’s entrance or exit of the Eastern Baltic Sea). It is remarkable that the ship size is higher in summer than in winter. A possible explanation might be the fact that cruise ships, which are generally rather large, mainly navigate the Baltic Sea during the summer months, which is reflected in the average value. Ship class categories All vessels of the traffic flow in the KDT were categorized according to class (see figure 7) in order to draw conclusions on the composition of the traffic flow and the ship types. Vessel classes were labeled A to D and defined in relation to the length, the draft and the vessel type [14]. Thus, ships classes serve as an indicator of the potential damage that a traffic participant may cause in case of an accident. The category, however, offers no immediate risk assessment since that directly dependents on the abilities of the nautical personnel as well as on the technical condition of the ship. Composition of the traffic flow The ship classes were used to study the composition of the traffic flow according to week days (see figure 8 first line). It was shown that ship classes B and C represent the main groups in the KDT, with the third largest group consisting of class A ships and the smallest group being class D ships. Considering the fact that ships of class D are longer than 200 m or tankers with a draft of more than 11 m, their share of 5 to 10 % is rather significant. For these reasons, vessels that are identified as tankers in the AIS are listed separately in figure 8 (bottom row of graphs). It can be observed that their number during week days is hardly affected by fluctuations. A comparison of northand southbound tanker movements (figure 8) reveals that the number of tankers leaving the area is higher than the number of tankers entering it. This might be explained by the fact that tankers moving southwards are loaded and have to sail the KDT because of their increased draft. Tankers entering the Eastern Baltic Sea can use the Öresund as an alternative route and profit from the shorter travel distance when passing through the Skagerrak (sea route north of Denmark). Heatmap and congestion Besides the analysis of single week days, we studied daytime congestion of the KDT (see figure 9, top), uncovering systematic differences. For this, we used the following Figure 5: Speed in the KDT from 01/ 2009 to 12/ 2014 Figure 7: Ship size development since 2009 Figure 6: Ship class categories STRATEGIES Maritime Traffic International Transportation (67) 2 | 2015 16 method: The daily and hourly numbers of southbound and northbound vessels were aggregated and then divided by the number of weeks under investigation in order to receive the average value. The data were visualized in a heatmap developed and adapted specially for this purpose. This map indicates an increased congestion in the early morning hours and during the late hours of the day. Thus, on week days between 6: 00 and 22: 00 o’clock, traffic flow is rather low. During the weekend, especially on Saturdays, traffic flow is significantly higher, especially around noon compared to the same time during the week. In contrast, the heatmap of tanker passages (see figure 9, bottom) is quite homogeneous and does not indicate increased traffic on particular days or times. It can be observed that the average traffic flow is only marked by minor fluctuations, with an average of 1.1 to 1.2 vessel passages per hour. Overtaking in the KDT Despite the challenges of the sea area due to the TSS, necessary significant course alterations of 80° and depth restrictions eastwards as well as westwards, overtaking maneuvers are regularly undertaken. During such a maneuver, a ship is identified as an overtaker if it was part of the traffic flow and entered the core area after and left it before the presumed predecessor. The resulting overtaking maneuvers of the different ship classes are represented in figure 10. The high number of overtaking maneuvers of class D ships is remarkable, especially in view of the fact that these ships are longer than 200 m or tankers with more than 11 m draft and a length of more than 100 m. Conclusion The Kadet Trench (KDT) is one of the most frequented sea areas of the world. Due to the local characteristics described, special care is required in ship navigation. In particular, night hours with more than 10 ship movements per hour, ships of class D and the number of overtaking maneuvers increase the risk of accidents. The situation often leads to news coverage in the media, discussions in politics and analyses by researchers. It is to be hoped that no major accidents will occur in the KDT, especially with southbound tankers. ■ LITERATURE  [1] Review of Maritime Transport, UNCTAD/ RMT/ 2013, Sales no. E.14. II.D.5 United Nations, New York and Geneva, 2014  [2] Serry, A.: Dynamics of maritime transport in the Baltic Sea: regionalisation and multimodal integration. In: 6th International Conference on Maritime Transport, Barcelona, June 25-27, 2014 Figure 8: Composition of traffic flow and number of tankers Figure 9: Congestion in the KDT, all ships and tankers Maritime Traffic STRATEGIES International Transportation (67) 2 | 2015 17  [3] Williams, D. W. (Hrsg.): Admiralty sailing directions: Baltic Pilot, Vol. 1. United Kingdom Hydrographic Office, London, 2004  [4] IMO: Resolution 620 A (15): Navigation Through the Entrances to the Baltic Sea: International Maritime Organisation, 1987  [5] International Marine Electronics Association (IMEA): NMEA 0183 V.4.1: Standard for Interfacing Marine Electronic Devices. Version of June 2012, Severna Park, MD, USA, 2013  [6] Hilgenfeld, C.; Hartmann, F.; Ahn, M.: AIS data as a basis for industry and science. HANSA International Maritime Journal 151 (2014), 8, p. 74-75  [7] Vojdani, N.; Ahn, M.; Hilgenfeld, C.: Aufbereitung von AIS-Daten der WSV-N für die Simulation von Seeverkehrssystemen. Fachgruppenworkshop. Arbeitsgemeinschaft Simulation. ASIM/ GI, Stralsund, June 18, 2015  [8] Roß, Th.: Kadetrinne: Die Tankerfalle in der Ostsee, http: / / www.ndr. de/ nachrichten/ kadetrinne115.html  [9] Hamburger Abendblatt (HAB): Greenpeace in der Kadetrinne. Hamburger Abendblatt, 12.12.2002, www.abendblatt.de/ wirtschaft/ article106777236/ Greenpeace-in-der-Kadetrinne.html [10] Hamburger Abendblatt (HAB): Experte fordert Lotsenpflicht in der Kadetrinne. Hamburger Abendblatt, 04.08.2010, www.abendblatt.de/ region/ norddeutschland/ article107831761/ Experte-fordert-Lotsenpflicht-in-der-Kadetrinne.html [11] Gamillscheg, H.: Warten auf die Katastrophe. (Öresund): Der Schiffsverkehr in der Ostsee nimmt stetig zu. Vor allem die steigende Zahl der Öltanker macht den Experten Sorge. Ostseezeitung, 30.11.2012, S. 3 [12] Gamillscheg, H.: Die Ostsee wird für den Schiffsverkehr zum Nadelöhr. Hannoversche Allgemeine, Nov. 2, 2012, http: / / www.haz. de/ Nachrichten/ Der-Norden/ Uebersicht/ Die-Ostsee-wird-fuerden-Schiffsverkehr-zum-Nadeloehr; accessed on Oct. 21, 2014 [13] Wikipedia: Kadetrinne, http: / / de.wikipedia.org/ wiki/ Kadetrinne; accesssed on July 1, 2015 [14] Ulusçu, Ö. S.; Altıok, T.; Or, İ.; Özbaş, B.: Risk Analysis of the Vessel Traffic in the Strait of Istanbul. Risk Analysis 29 (2009), 10, p. 1454- 1472 Frank Hartmann, Dipl.-Ing. Department of Maritime Studies,at University of Applied Sciences Wismar (DE) frank.hartmann@hs-wismar.de Carsten Hilgenfeld, Dipl.-Ing. (FH), M.Sc. Department of Maritime Studies, University of Applied Sciences Wismar (DE) carsten.hilgenfeld@hs-wismar.de Manfred Ahn, Prof. Dr.-Ing. Professor for Traffic Planning and Urban Planning, University of Applied Sciences Wismar (DE); Steinbeis- Transfer-Institute Laws, Economics and Operations manfred.ahn@hs-wismar.de Nina Vojdani, Prof. Dr.-Ing. Head of the Chair of Production Organization and Logistics [LPL], Faculty of Mechanical Engineering and Marine Technology, University of Rostock (DE) vojdani@uni-rostock.de Figure 10: Passing maneuvers in the traffic flow The German Partnership for Sustainable Mobility Sustainable Mobility - Made in Germany What we offer Publications → Mobility and logistics knowledge, concepts, expertise, and products made in Germany → Information tailored for planners and decisionmakers worldwide → Access to notable experts in Germany → Networking and professional connections → Information on financing options W W W . G E R M A N - S U S TA I N A B L E - M O B I L I T Y . D E Consulting in Sustainable Mobility - Made in Germany W W W . G E R M A N - S U S TA I N A B L E - M O B I L I T Y . 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