Case Study: Izmir, Turkey


  • ESHOT is the municipal-owned operator of the bus network in Izmir and its surrounding service area. It operates a fleet of 1,560 buses, including 410 from its associate Izulas.
  • The bus network forms part of an integrated transport system including Metro, Rail, Ferry, and local paratransit. Integration has been developed since 2000, and suburban rail was included in 2010.
  • The Izmir Metropolitan Transport Co-ordination Centre was established in 2006 for the planning, co-ordination and determination of routes; ESHOT is represented on this body through its General Manager.
  • The company has implemented extensive ITS since 1999, when smart-card ticketing was first introduced. The ticket validators have provided the backbone of the on-bus intelligent network.
  • Vehicle location and voice/data communication capability have been added to provide the platform for a new AVM system. This is based on a centralized Control Centre that manages services on a real-time basis.
  • The AVL supports real-time passenger information on buses and at bus-stops. The communications capability is also utilized for surveillance.
  • AVL data is also utilized for fuel issue monitoring and bus maintenance scheduling.

Scope of the Case Study

This case study deals with the ITS implemented at ESHOT, the municipal bus operator in the metropolitan area of Izmir. It does not cover the ITS implemented at the metro, rail or ferry operators, except where this is directly relevant to the ITS implemented at ESHOT.

Likewise, it does not cover ITS implemented by the city for traffic management or other transportation services, again except where it is relevant to or interfaces with the ESHOT ITS.

Due to the central role of the e-ticket on-bus validators in the ITS implemented at ESHOT, the technology is covered in this Case Study insofar as it forms part of the ITS platform and the development / migration path. The fare collection aspects and related functional / technical requirements are covered in the corresponding Case Study in the Fare Collection Toolkit.



Izmir is Turkey’s third largest city (after Istanbul and Ankara) and has developed over the past 3,500 years around the Gulf of Izmir off the Aegean Sea. It now comprises 11 metropolitan districts brought together under unitary authority, and a further 10 districts are wholly or partially included in the new municipal arrangements.

Izmir Metropolitan Municipality had a population of some 3.35 million in 2010, with the peri-urban area adding a further 0.6 million. Population increase in the municipality over the past decade has been some 50%, primarily because of recent boundary changes but also because of inward migration and natural growth.

Public transport in Izmir consists of the following:

  • Urban bus services, operated by ESHOT and Izulas, with 1,560 vehicles
  • Urban ferry services, operated by Izdeniz; 24 ferries, using 8 quays
  • Metro rail, operated by Izmir Metrosu; 1 line, launched in 2000
  • Suburban commuter rail, operated by IzBan; 2 lines, launched in 2010
  • Peri-urban/hinterland bus services, operated by ESHOT
  • Hinterland paratransit services, operated by dolmus

Urban bus is the main means of public transport in the municipality, providing citywide coverage and carrying 86.5% of all passengers in 2010; metro carried 9.5% of passengers, ferries 3%, and suburban rail 1% (part year).

No data were made available on public transport mode share, although this varies greatly across the metropolitan area. Public transport has a relatively high modal share for trips entering the central area during the peak hours (>50% on some corridors). This quickly tapers off with distance from the centre. Private car is the dominant mode outside the center, and paratransit dolmus (minibuses and shared taxis) provide most of the public transport for suburban and peripheral travel. Cycling and walking have low mode shares, despite being favored in policy terms. Taxis are deregulated, plentiful, and relatively expensive (fuel is heavily taxed), and have a low share of the total travel market.

Public transport developments in recent years have focused on the rail modes, and this is planned to continue under the Egeray program launched in 2006. The metro line is currently being extended at both ends, and new lines are planned. Suburban rail services were launched in 2010, and new lines will be added through to 2017. Four new light-rail tram lines are also included in the program.

However there has also been considerable renovation and expansion of the ESHOT bus fleet in recent years, introducing both low-floor and articulated buses and adding air-conditioning to nearly half of the vehicles. No plans for bus-based rapid transit (BRT) were advised, though.

The primary means of private travel demand management is parking control, with strongest enforcement in the central areas and in suburban hubs. This is primarily based on dissuasive pricing mechanisms, and to a lesser extent on quantity control. However observation suggests that this is not wholly effective.


Regulatory Framework

Regulation of Passenger Transport

A major transformation of public transport in Izmir commenced in 2000, with the launch of the Integration project. This brought together the new metro line, the ferry operations (taken into municipal ownership at that time), and the bus network. This integration was supported by infrastructure investment in new transport hubs at the points of interchange.

A Transport Co-ordination Centre (UKOME) was established within the Izmir Metropolitan Municipality for this purpose, with its powers formalized by Regulation in 2005; UKOME reports directly to the Mayor. The centre covers all modes of public transport, as well as car parking, within the municipality. This institutional reform has now been replicated across Turkey under Articles gazetted in 2006.


Basis of Service / Route Award

UKOME provides the strategic direction for the development of an integrated passenger transport network, including the Egeray program of rail-based transit systems. ESHOT is required to integrate its service offer with other modes, and major investments in interchange facilities have been made in recent years.

The process of integration has been facilitated by a tariff structure that now allows unlimited interchange within a 90-minute period that is enabled through the smart-card e-ticketing system. This development is reported in the parallel case-study for the Fare Collection toolkit.

Within these constraints, ESHOT holds a monopoly for bus-based transit in the urban area and has the freedom to develop and adapt its service offer. However its services in the hinterland of the city are sparse, and local passenger transport there is largely provided by private paratransit dolmus (minibuses and shared-taxis).


Permits or Contracts

ESHOT has a Public Service Obligation (PSO) to carry students and teachers at discounted fares, and the disabled and pensioners for free.

As Greater Izmir has 7 universities (with another 2 planned), the numbers qualifying for discounted fares is very considerable. In the academic year 2010-11, some 250,000 student cards had been issued and a further 17,500 teacher cards.

There are also some 114,000 privilege (free-travel) cards in issue, of which the main categories are: disabled, 55,000; disabled helpers, 6,000; pensioners over 60 years, 49,500; and pensioners over 65, 2,500. Certain categories of municipal service staff are also entitled to free travel when on duty, and 600 anonymous cards have been issued that must be supported by official identification.


Allocation of Revenue and Cost Risks

Revenue and Cost risks theoretically lie with ESHOT, which is required to operate commercially against budgets approved by the Izmir Metropolitan Municipality. However the financial losses arising are covered by the Municipality, and are calculated to be less than the lost value of the services provided under Public Service Obligation.

Tariffs are set by the Izmir Metropolitan Municipality, based on advice from UKOME. In mid-2011, the standard fare in the urban area was TRY 1.70 (USD 1.10) and the discounted fare TRY 0.90 (USD 0.58). This covers any direct or interchange journey completed within 90 minutes of the first boarding.

However the revenue allocation for passenger journeys involving interchange between ESHOT and other modes is formulaic, derived from agreements negotiated between the operators. This formula allocates revenues in favor of the mode first boarded, but may be expected to equalize over the typical daily commute where journeys are reversed.

It should be noted that over 25% of ESHOT passengers also use another transport mode to complete their journey, and hence the sums involved are significant. The revenue allocations are managed within the clearing-house function of the e-ticketing system integrator, and a reconciliation is made every midnight.


Institutional Framework

Public Transport Operators

ESHOT was first formed in 1943 to take the Izmir Tram and Electric Company into municipal ownership; trolleybuses were added to the system in 1945. That year, ESHOT also took over the Izmir Coal Gas Company, and added the Izmir Water Company in 1947 to form an integrated utility enterprise. The ESHOT acronym was then formed from the Turkish for electricity, water, coal-gas, bus, and trolleybus.

However the tramways were in decline even when ESHOT was formed, and the system gradually contracted until the last line ceased operation in the early 1960s; trolleybuses continued in service until 1992, though. In 1982 the electricity operations of ESHOT were nationalized, and a new Izmir Water Company was formed in 1987. In 1994 the coal-gas plant was closed, leaving ESHOT purely as a bus company but retaining its original name.

ESHOT operations incorporate an associate company, Izulas, whose fleet largely comprises minibuses and smaller vehicles more appropriate for operation in historic areas of the city where highway standards preclude large buses. Izulas is still a private company, but fully integrated into the ESHOT systems and sharing several of its depots.

Izmir Metro is the undertaking established for the development and operation of the underground rail network in Izmir. Construction commenced in 1995, and was completed some four years later. The system came into public service in May 2000. Ownership is 60% at the national level and 40% at the municipal level.

The initial line of 11.6km runs along the southern shore of the gulf and through the city centre, and has 10 stations. This line is currently being extended at both ends, and branch extensions are also planned when that program is completed.

Izdeniz is the company formed in 2000 when the ferry services in the Gulf of Izmir were taken into municipal ownership as part of the Integration project. However it retains the structure of a private company, and hasn’t yet received the investment applied to other modes.

24 ferries shuttle between 8 quays positioned around the gulf in the main urban area, and additional services are provided to points further out in the gulf during the summer months for the tourist and excursion markets. All ferry terminals are equipped with turnstiles for smart-card validation, and the traditional jeton payment was discontinued in 2011.

IzBan is the company formed in 2006 for the development and operation of a suburban commuter rail network in Izmir under the Egeray program. It is jointly owned by Turkish State Railways and Izmir Metropolitan Municipality. It is the only such joint-venture entered into by the railway.

Operations commenced in 2010 with lines running south and north-west from the city centre and totaling 80km with 31 stations. Apart from the infrastructure upgrade of existing track alignments, including 2 new tunnels, grade separation, and 5 new stations, 15 new bus terminals were built for integration with ESHOT bus services. All stations were also fitted with turnstiles for incorporation within the city-wide smart-card e-ticketing system.

Local Authorities

The city of Izmir is currently composed of eleven metropolitan districts: Balcova, Bayrakli, Bornova, Buca, Cigli, Gaziemir, Guzelbahce, Karabaglar, Karsiyaka, Konak and Nardilere. Each of these was a former district center absorbed into the expanding metropolis, with Konak district corresponding to historic Izmir and still forming the core of the city.

A further 10 surrounding districts fall under the remit of the Mayor of Izmir in respect of certain administrative functions, including passenger transport. For that purpose, though, the service area is defined as a 50km radius from the city centre and not strictly by district boundaries.

ESHOT Structure

ESHOT operates as five divisions in the urban area, with two minor sub-divisions in the hinterland of the city. The numbers of routes operated by each division, and the vehicles allocated to each are as follow:

Division Routes Vehicles ESHOT Izulas
Buca 50 328 308 20
Konak 74 306 266 40
Bornova 60 378 235 143
Karsiyaka 80 375 305 70
Teleferik 40 287 272 15
Torbali 13 24 24 0
Urla 3 8 8 0
Total 320 1,706 1,418 288

note: Vehicles include the ancillary fleet; service buses total 1,561.

The large majority of the fleet are standard-length single-deck buses, but 200 articulated buses were introduced from 2008 and 42 new mini-buses added to the Izulas fleet in the same year. 744 of the buses are now air-conditioned (including retro-fits), and 444 have low floors and step-less entry equipped for wheel-chair access.

The major investment program from 2007 onwards has increased the fleet from 1,120 to 1,560 buses, and reduced its average age to 8.91 years. 90% technical availability is achieved, now providing 1,400 buses for daily operation.

ESHOT operates from twelve depots, of varying sizes, most of which are located in the city and inner suburbs; five of these depots have full workshop facilities.

Key daily metrics for ESHOT operational performance are:

Fleet operated         1,400

Departures                11,000

Kilometers                320,000

Passengers                1.3 million

Kilometers/bus        230

Passengers/bus         930

ESHOT had 3,760 staff in 2009, of whom 2,768 were drivers. This is a ratio of 2.7 staff per operating bus.


Implementation of Intelligent Transport Systems at ESHOT

Motivations to implement ITS

The principal motivations to implement ITS at ESHOT have been to:

  • Develop a secure and effective revenue collection system – this has formed the backbone of the subsequent ITS applications
  • Enable modal and service integration through minimizing personal costs of interchange
  • Develop enhanced operations management capacity to provide reliable services and deal with disruptions
  • Provide improved passenger information in real-time
  • Provide surveillance for passenger and personnel security
  • Obtain data for planning, resource optimization and performance monitoring

Overview of ITS deployment at ESHOT

ITS at ESHOT has been deployed and enhanced over an extended period, in most cases building on the strengths or capabilities of previous implementations.

The deployment path of ITS systems at ESHOT is summarized as follows:

1999                Introduction of smart-card e-ticketing on pilot basis

2004                Completion of e-ticketing roll-out for all travel on ESHOT

2006                Automatic vehicle location implemented

2007                Introduction of transferable tickets across modes on pilot basis

2008                Completion of transferable tickets across all modes

2009                Fuel issue and stock control system

2009                Operations Control Centre

2010                Real-time passenger information at bus-stops and on buses

2010                Passenger surveillance systems

The smart-card e-ticketing system was the first ITS system at ESHOT, and was originally intended as a stand-alone application. However the on-vehicle validator that was developed by the local equipment supplier had embedded capabilities for automatic vehicle location, as this had been required for another city introducing e-ticketing at the same time.

The validator was also equipped with a communications capability, initially to receive ‘black-lists’ of invalid smart-cards, and this could be adapted to AVL, RTPI, and surveillance applications. The e-ticketing validator has therefore provided the data center and intelligent hub for all subsequent ITS applications at ESHOT.


Intelligent Transport System Applications at ESHOT

Automated Fare Collection

This application is covered in greater detail in the case-study on fare collection in Izmir for the parallel World Bank toolkit currently being developed for that topic. The following is a summary of the key implications of the application for the subsequent deployment of other ITS systems at ESHOT.

Electronic ticketing was introduced to Izmir in March 1999, with the Akilli Kart. This employed Korean technology for the contactless smart-card and validator, and a Motorola communications system. At this stage, this was a standalone application designed to improve revenue integrity and protect against fraud.

However the system integrator contracted by ESHOT for this program found that working with foreign suppliers was problematic, and it was agreed that this should be replaced by locally designed and manufactured hardware. This was applicable not only to Izmir, but to 3 other cities in Turkey with which the system integrator was working at that time.

The benefit of this local development was that the equipment was designed for a range of applications identified by the different cities, and was compatible with all industry-standard smart-cards. The supplier claims a world first for the integration of Automated Fare Collection and Vehicle Tracking Systems in a single unit as a result. Communications were also migrated onto GPRS, removing dependency on a dedicated wireless network.

In the initial application conventional paper tickets retained validity, and a special card allocated to each driver was used to enter the travel details for passengers who didn’t hold a smart-card – now known as KentKart (CityCard in Turkish). This card has been retained and adapted for other applications, even though it is no longer needed for the fare collection system after all driver involvement in that process ceased in September 2009.

In February 2007 a pilot application for transferable tickets between modes was launched initially involving ferries, metro, and 100 buses on 52 routes that provided feeder services. This offered a 50% discount on a second boarding made within 60 minutes of the first, and hence required the timed transactions to be written to and read from the smart-card.

This transfer capability was extended to a 90 minute validity in January 2008, and the discount for any subsequent boarding increased to 100% in August 2008. In effect, this has introduced a flat-fare structure for passenger transport across Greater Izmir for all holders of smart-cards.

Because of this fare structure, ESHOT buses are only fitted with ticket validators at the entrance door and there is no need to revalidate at exit. Although not needed for the fares validation, the transaction records the location of the bus at that time using the automatic vehicle location capability of the validator.

As a result, travel path data availability gathered from ticketing transactions is only partial in that any points of interchange are captured but not the point of final alighting. Nevertheless this can be determined for regular commuting journeys from the point of first boarding for the reverse trip.

ESHOT has used the travel path data generated from the ticketing transactions, and the freedom provided by the elimination of interchange-costs from the new fare structure, to recast its route network. This has now been directed towards planned interchange both with the rail modes and ferries, and within the bus mode itself using purpose-built hubs. As a result passenger numbers have been significantly increased, and long and unreliable routes have also been reduced to the benefit of service quality.

Automatic Vehicle Management

As noted above, the KentKart on-vehicle validator has always had an automatic vehicle location capability even though this wasn’t activated in the initial application of the e-ticketing system. However, once that application had been completed in 2004, ESHOT and its ITS system supplier then started to develop an automatic vehicle management system which was implemented progressively from 2006.

In its first phase, this just provided an on-line vehicle tracking capability. Each bus is ‘polled’ on a 10-second cycle, and its GPS location is then transmitted back to the operations control function; the cost of this GSM transmission is some €20 per bus per month.

This information was then used primarily for control of departure timings, especially at the outer terminals of routes where the level of supervision was necessarily low. However it also enables any route violations to be detected by cross-checking against the co-ordinates of the route to which the bus is currently assigned.

These data also allow for the speed of the vehicle to be calculated, which was then deemed to be of particular significance for the ancillary fleet. This information is now displayed on the buses, as part of the RTPI package, and a telephone contact number given for passengers to report inappropriate driving.

The vehicle location information is now reviewed on a route by route basis in order to examine the actual service headways being experienced, and identify whether any bunching is starting to occur. Should that be the case, then buses getting too close to the one in front are instructed to hold back and let the headway open out again. This is achieved by longer dwell times at stops and slower driving, with no special provision being made for hold-over points along the route.

Relatively little emphasis is placed on adherence to schedule, as it is not usually possible for a bus running late to make up time. As such, operations control actually increases delays for all vehicles on the route, and hence for all passengers who plan their trips according to the timetable. However vehicle loading may become more even as the headways are regularized, and service quality be improved as a result.

The operations control centre at ESHOT was upgraded in 2009, but the company recognizes that this is still basically a reactive ‘monitoring’ unit rather than a proactive ‘management’ unit. The system integrator estimates that the current deployment of AVM is only reaching some 30% of its potential, and that there is thus a need for reform of operations management practices.

The next planned development, therefore, is to move the operations management information from the center down to the divisional hubs. Local managers will then be given authority for dynamic rescheduling, and the deployment of a ‘hot reserve’ for schedule restoration. In this manner, schedule restoration becomes a realistic objective as well as improved response to service disruptions. The main obstacle identified for this initiative, though, is the suitability of different sizes of buses for specific routes – and hence the scale of the reserve fleet that is required at each location.

However the operations control center does also link the surveillance functions, the emergency response capability, the communications network, and the internal efficiency control systems. As such, it will retain its importance for ESHOT even as the responsibility for operational control is devolved. The respective functions served by the center will be covered in later sections of this case-study.

The AVM system generates a range of reports for management information purposes. These include:

  • Route violation report
  • Daily total kilometer report
  • Speed-band / time-duration graphic
  • Speed violation report
  • Schedule adherence report

Passenger Information Systems

ESHOT have developed real-time passenger information systems at two separate levels – at bus-stops, and on the bus itself. At this stage, the vehicle tracking information generated by the AVM is not posted on-line for dynamic route planning, and the website only hosts traditional route schedule information.

The basic data for the RTPI application are generated from the AVM vehicle tracking application, and the identification of the route variant that each bus is serving. The resultant information is transmitted to dot-matrix displays in the bus shelters, and these are configured so as to provide full data for the next two expected arrivals or summary data for the next four arrivals with the display toggling between these.

In each case the information display shows the identifying number of the route being served, and the number of stops away from the shelter that the nearest bus is currently positioned; the full data display adds the destination terminal of the route number in question. The displays can also show schedule changes, or any other summary information of importance to travelers.

The selection of the number of stops away, rather than the expected delay to arrival, was a pragmatic choice based on the impact of congestion in much of the network in which there is very little public-transport priority. It was felt better by ESHOT to give accurate information that could be interpreted by passengers, rather than more useful information that had the potential to frustrate if it proved to be inaccurate.

At the current time, the bus-stop information displays are still being rolled out in a pilot program with only a small minority of the nearly 6,000 shelters now being so equipped. Whether because of the restricted coverage, or because the information was not found to be of great value on the high frequency routes serving these shelters, observation suggests that the displays were generating little interest and that travelers still looked up the road for the arrival of their next bus.

Discussions confirmed that the information displays would have greater benefit on low-frequency routes in the periphery of the network, but that the required investment would be more difficult to justify under those circumstances where the numbers of travelers would be relatively small.

However there is also an enquiry service, whereby travelers are able to learn when a bus is expected to arrive at their stop, using a SMS text message via GPRS on their personal cell-phone. It is likely that this will form the predominant means of real-time passenger information in the peripheral areas for the foreseeable future.

The on-bus passenger information system comprises a 19” VGA color video screen on which a graphic of the route and its immediate surroundings is displayed. The screen shows the position of the bus in real time, and also its speed. Announcements are made concerning the current or approaching bus stop.

The system therefore provides on-vehicle route tracking for passengers, and enables them to prepare for alighting at the appropriate stop. However it doesn’t provide the expected time of arrival at the main interchange points along the route, which might be of concern to passengers intending to make a linked journey.

The passenger information unit can also provide news feeds and weather forecasts, and hence provides an ‘infotainment’ capability. Finally it provides point-of-contact details for ESHOT should passengers wish to provide personal feedback on driver behavior or standards.

Mobile Video Surveillance System

The MVS system at ESHOT consists of a mobile digital video recorder and wide-angle cameras appropriately located within the bus. The MVS system also takes vehicle tracking and speed data from the AVL capability of the smart-card validator. Finally the GPRS communications capability links the collected data through to the operations control centre when needed.

The recorder is provided with a smart memory card that can be used to take visual evidence of an incident into secure keeping for any subsequent investigation or prosecution. It also has ports for the downloading of data as required for management information purposes, and for direct GPRS wireless transmission if required.

The primary function of the MVS system is integrated recording of AFC transactions in order to identify the perpetrators of any attempted fraud. However this system also provides some deterrent protection against attacks on the driver in that visual evidence is captured. In the event of an attack, a driver emergency button connects the incident direct to the control centre for a rapid support response.

From an operations management perspective, the MVS system provides for the recording of any traffic incidents and collisions, including deceleration sensors to identify the severity of the impact. It also monitors the boarding and alighting of passengers, and any disturbance at the shelter while the bus is stationary. This surveillance provides personal security, and helps to protect ESHOT from any spurious claims for damages.

ITS-Facilitated Functions

ESHOT also uses the data generated by its ITS systems in order to improve the overall effectiveness and efficiency of its service delivery, as summarized below.

The automated fare collection system, and its integrated automatic vehicle location function, provides a wealth of data about individual travel patterns in terms not only of origins and destination but also of points of interchange. These enable the recasting of the bus-service network in response, and to improve integration with the other transport modes in the metropolitan area.

The automatic vehicle location function enables measurement of travel times, and their variations (both by time of day and direction of travel), between nodes within the bus network. In this manner bus schedules can be made more achievable, and any vulnerabilities be detected for management intervention. Dynamic rescheduling is now planned under decentralized operations management.

The ESHOT fuel management system takes data directly from the driver card onto a reader at the pump so as to allocate issues to the appropriate vehicle, and to upload the kilometers run by the bus into the system; this avoids any transcription errors that are typical of manual systems. The data link from the pumps to the control center also carries the stock levels in the bulk-fuel tanks, and integrates with the re-ordering function. Exception reports are generated that can identify drivers or buses with abnormal fuel consumption rates.

Finally, the kilometers operated by each bus are also used to inform the preventive maintenance function and to schedule planned interventions accordingly.


Capital Costs of the ITS

This data is not in the public domain and has not been made available.


Operating Costs of the ITS

The only operating cost that was directly attributed to the ITS was the GSM polling cost of the vehicle tracking system, which was reported as being some €20 per bus per month.


Revenue Generated by or through the ITS system

There are no incomes directly generated by the ITS systems, other than the Automatic Fare Collection application.


Benefits arising from the ITS systems at ESHOT

The achieved/perceived benefits of the ITS investments at ESHOT are viewed separately for the automated fare collection system, and for the various other ITS applications. Benefits of the ITS systems have not been quantified, and it does not appear that it was felt necessary to do so. In the case of the AFC system, the benefits are regarded as self-evident; in the case of the other applications, the systems are mostly still under development and haven’t reached their full potential.

However the system integrator has a close working relationship with ESHOT, and is developing its applications in response to the emerging needs of the operator. By meeting those expectations, it has secured two contract renewals since the initial AFC award.

For the fare collection system, the main benefits reported are:

  • Improved revenue generation through reduction of fraud and peculation
  • Elimination of cash handling, security and administration costs of traditional paper tickets
  • Accelerated fleet investment, enabled by improved operating cashflow
  • Greater network efficiency arising from planned interchange, enabled by the through-ticketing capability and elimination of transfer charging
  • Increased ridership as a result of the network integration, though this is of more significance to the rail-based modes

For the other ITS applications, the main benefits reported are:

  • Improved operational control, though in a reactive rather than proactive sense
  • Improved real-time passenger information, especially on-board the bus
  • Enhanced security through on-board video surveillance
  • Generation of data on service performance, and their incorporation into more accurate schedules
  • Automation of data collection for management information and preventive maintenance scheduling