Chapter 6 Traffic Management

The Study on Integrated Urban Transportation Master Plan for Istanbul Metropolitan Area in the Republic of Turkey Final Report Chapter 6 Chapter 6 Traffic Management Various kinds of traffic management measures are already in place in the study area. They are intended to improve efficiency as well as the safety of road traffic in general. This chapter describes typical traffic management measures and systems being adopted in Istanbul. In addition, traffic accident situation and enforcement of traffic regulation are also presented. 6.1 Traffic Signal System 6.1.1 Existing Signal System There are some 1300 traffic signals in Istanbul. Among them, about 800 signals are connected to the Traffic Control Center located in the municipality building in Merter. All hardware and software components of the system have been developed locally including signal controller, signal light and control software. A unique approach has been taken in the design of the system as described below. Cellular phone technologies are adopted in the traffic control system and data communication between the local controller and the Center uses TCP/IP1 protocol over GPRS2. No data exchange is made between the Center and the local controllers under normal condition. Local controllers independently operate in a time-of-day mode with its built-in timing parameters. In area traffic control (ATC) system commonly adopted in other cities, the data exchange between the center and the local controllers is much more frequent and normally done at one second intervals. In such system, signal control command and other downloading data are sent to the local controller, while local controller status data and vehicle detector data are sent to the Center. With the frequent data exchange between the local controller and the center, traffic signal operates very efficiently with traffic adaptive or traffic responsive control algorithms. The Istanbul system was built based on the policy to reduce data communication costs as much as possible and limit the data exchange to a minimum. The use of GPRS achieves the goal but there is a risk associated with less frequent data transmission. If an emergency happens, the communication circuit could be congested and the data communication would not work properly. If local controller detects any abnormality in its operation, it automatically informs the Control Center of the controller’s status. On the other hand, it is possible to interrogate each local controller and determine its operating status from the Center anytime. Moreover, the data stored in the local controller can be uploaded or Source : Study Team downloaded through the data communication system. Figure 6.1.1 Camera Detector on Top of Signal Lantern 1 Transmission Control Protocol/Internet Protocol: A data exchange technology used in Internet. 2 General Packet Radio Service: Data transmission system over GSM (Global System for Mobile communications) cellular phone system. 6-1 The Study on Integrated Urban Transportation Master Plan for Istanbul Metropolitan Area in the Republic of Turkey Final Report Chapter 6 Signal control is of the time-of-day type, in which each local controller has four sets of timing plan and the different plans are applied according to the time of the day. Thus signal operates with different systems timing at different times of the day to cope with the change in the traffic volume. Flashing operation is also possible by time-of-day control. In addition to the existing inductive loop vehicle detector, traffic camera type vehicle detector was introduced recently and there are 100 units of the detector in operation. They detect presence of vehicles within its sensing zone and output the presence signal to local controller to enable actuated signal control. If an approaching vehicle is detected near the end of green, green signal is extended to allow the vehicle to pass the intersection without stopping. On the other hand, if no vehicle is detected, green signal is cut shorter than the preset duration. Such operation is effective in reducing the total waiting time at intersection. The actuation control is, however, not used to a series of signals closely located along an arterial street to maintain a “green wave” or offset between signals. 6.1.2 Traffic Signal Design and Maintenance New signal is designed in the following manner: Geometric design of intersection is undertaken by Transportation coordination Directorate. Traffic Directorate will then design signal, and the location of signal post and local controller is decided. Minor modification of intersection design may be made but basic element such as road width or bus stop location cannot be changed. ISBAK, a company established by the Municipality engaged in signal installation and maintenance, carries out detailed design of signal including signal timing calculation. Commercially available signal timing software was used before. But the results were found not directly applicable to the signals in Istanbul. For example, SYNCHRO tends to produce longer timing than necessary. ISBAK wants to try any signal timing software that can produce better results than those they have used. In reality, the signal timing and coordination (green wave) is prepared based on the traffic volume data, site observation and the experience with the signal design at similar intersections. The signal timing software is used only to confirm the adequacy of the calculation. No evaluation study has been made comparing traffic condition before and after the signal installation or signal timing updating. The signal maintenance and timing plan updating system is organized as follows: Whole Istanbul is divided into five areas. For each area, two teams are assigned and each team consists of two members; electronic engineer and computer engineer. They work in two shifts with first shift from 06:00 to 14:00 and the second shift from 14:00 to 22:00. There are 31 staff in total. Maintenance team routinely patrols the area assigned and checks the suitability of signal timing. If timing is found not properly set, the team modify the timing on the spot using notebook computer connected to the local controller. The existing signal system still uses loop detector at about 300 locations. Because of inferior pavement condition, 30 – 35 % of them are always not working and maintenance 6-2 The Study on Integrated Urban Transportation Master Plan for Istanbul Metropolitan Area in the Republic of Turkey Final Report Chapter 6 of them is very difficult and costly. In order to reinforce the signal maintenance capability, additional four engineers are scheduled to join the team. They will engage not only in the review and updating of the signal timing but also in the design of traffic management improvement plan. 6.1.3 New Signal System There is a movement to improve and upgrade the existing traffic signal system. In 2008, the Municipality is planning to introduce local adaptive signal control system. More sophisticated signal control software will be installed in the local controller and signal timing will be automatically adjusted to the changing traffic volume. Traffic Directorate is also planning to introduce centrally operated dynamic traffic signal system in which signal timing is automatically adjusted in response to traffic demand. The candidate system to be introduced is called ITACA and supplied by SAINCO TRAFICO of Spain. The location of the pilot project has not yet been decided. Traffic Directorate is aware of the limitation of GPRS data communication system and planning to introduce a system using fiber optical cable. In the new data communication system, 9600 Baud data transmission circuit system will be leased from a telephone company but the cost is very high at US$120 per month per circuit or traffic signal. In comparison, the Municipality currently pays only US$5.000 per month for the data communication using GPRS of the existing traffic signal system. 6.2 Traffic Monitoring System Traffic on the major streets in the city is monitored through two systems; CCTV (closed circuit television) monitoring system and vehicle detector system. A total of 116 units of CCTV cameras are installed and 60 unit are planned mainly along the expressways and arterial streets. The cameras are equipped with pan, tile, and zoom function that can be remotely operated from the Center to control the video coverage. These cameras send live video image of the site to the control center through the communication line leased from a telecommunication company. The system adopts MPEG4 3 data compression technology over 2 Mbits/sec circuit. Due to the reduced frame rate, the video image on the monitor display is not as smooth as images that use higher speed communication lines. But it is sufficient to monitor traffic flows. A large multi-screen wall map display measuring 15 columns by 5 rows capable of showing a maximum of 75 separate displays is installed at the Center. The wall map is also capable of showing a display over multiple screens from both video images taken by CCTV camera and other computer outputs. The operators in the Center constantly monitor traffic conditions through the video image on the wall map. As the number of cameras is more than the number of multiple screens, the operator has to select the sites and cameras to monitor the specific location. In addition, watching as many as 75 screens constantly is a daunting task. 3 MPEG4: Moving Picture Coding Experts Group 4. One of the video signal compression methods. 6-3 The Study on Integrated Urban Transportation Master Plan for Istanbul Metropolitan Area in the Republic of Turkey Final Report Chapter 6 Source : Traffic Control Center, IMM Figure 6.2.1 Location of CCTV Camera, 2007 RTMS4 type vehicle detector is also installed at 279 locations along expressways. They detect vehicle within its sensing area and produce such data as traffic volume, average speed and average time occupancy for multiple lanes simultaneously.

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