Signaling systems are the systems that provide unsur safety olan which is indispensable for rail systems such as Tram (SIL2-3), Light Metro and Metro (SIL4) by performing the related processes in the most timely and reliable way. These systems offer great technical, managerial and cost advantages as well as security.
Although the use of rail systems in our country is not very common until the 90s, we see that rail systems are increasingly preferred to solve the increasing traffic problem. Let us continue the article by explaining the basic signaling concepts for rail systems.
SIL (Safety Integrity Level)
SIL certification refers to the reliability of the system. The SIL level is expressed in the basic 4 levels, and as the SIL level increases, the security level increases with the complexity of the system to minimize risks.
SIF (Safety Instrumented Function)
The main function SIF here is to identify and prevent the dangerous situation that may occur during a process. All SIF functions form the SIS (Safety Instrumented System). SIS is the control system that controls the entire system and makes the system safe in hazardous situations.
The term Emniyet Functional Safety ise refers to the reduction of risk to an acceptable level by operating all SIF functions in the system.
Automatic Train Stopping (ATS)
In order to ensure safe and efficient train traffic in railway operations, different train control systems have been developed and some of them are (ATS) automatic train stop, (ATP) automatic train protection, (ATC) automatic train control.
ATS system is a security system that enables the stopping of the train by controlling the speed of the train where the traffic is controlled by electrical signals and also alerting the driver if necessary.
The ATS system mutually controls the speed of the trains with the information on the onboard equipment by means of magnets placed along the way and the signals next to them.
Automatic Train Protection (ATP)
The ATP system is a protection system that intervenes at the point where the driver does not fall to the required speeds or stop the train in line with the information received from the ATS system.
Automatic Train Control (ATC)
Although it is similar to the ATS system, it adjusts the speed of the train according to the position of the trains in the front and rear. Unlike ATS system, opening / closing doors and so on. security processes are also managed by ATC.
In the early years of the rail systems, no safety measures were required because of the low train speeds and traffic density. Amiyane, the security engineer. Although security was tried to be provided by using the time interval method with the pointer officers with the accidents experienced, security was started to be provided by the distance gap method and signaling systems with the increasing traffic density in the following process.
In summary, time interval method was used in the first years of the rail systems, and later distance interval methods were used, which is provided by signaling systems. Today, the use of signaling systems has made it possible to drive trains automatically without the driver.
The signaling system can be examined in 2 sections as Field Equipments (Rail Circuits, Automatic Shears, Signal Lights, Train Communication Equipment) and Central Software and Interlocking.
Rail circuits (Train detection); There are 4 types of Isolated Algebraic Rail Circuits, Coded Rail Circuits, Axle Counter Rail Circuits and Moving Block Rail Circuits.
In Isolated Algebraic Rail Circuits, if there is a return voltage according to the voltage applied from the isolated region, there is no train in the rail region and if there is no return voltage, there is a train. It is assumed that there is a train here in case of a possible failure.
Coded Rail Circuits use audio frequency, and a change in the signal means that there is a train on the track. The use of this system in short distance and uninterrupted locations is very useful in terms of safety and cost.
Rail Circuits with Axle Counters are systems that provide security by detecting the location of the train by counting the axles entering and leaving the rail. Their use in the world is increasing rapidly.
Moving Block Rail Circuits use virtual blocks whose length varies according to the speed of the train, stopping distance, braking power, curve and slope parameters of the region.
Use of Signaling Systems
In the flat and sighted areas, visual driving is used, while in the scissors and tunnel zones, the interlocking system is used to decide the entry and exit of a train to the corresponding switch. Interlocking system is basically the system that locks any rail on the rail that the train wants to enter and prevents the train from entering.
With the use of Fully Automatic Driverless Systems, the human factor which is the biggest factor of accidents is minimized. With these systems, accidents can be prevented by instant detection of trains, while waiting distances of passengers are shortened by reporting distances between trains and productivity is increased with high operational flexibility. These systems are also advantageous with low maintenance costs.
Today, fixed subway and subway stations mostly use Fixed block manual driving, Fixed block automatic driving and Moving block automatic driving signaling systems.
Fixed block manual drive
Generally 10 min. In this system, which is used at distances below, the relevant route of the train is 10 min. It is also assumed to complete. At this point, the driver's ability to cover this distance in a shorter time than this time can cause accidents. At this point, Machinist Information Systems (DIS) and Vehicle Tracking Systems should be used.
Fixed block automatic driving
Although it is approximately 20% more expensive than the manual driving system described above, it is possible to use the line more efficiently with automatic driving of the train and energy costs. Since the block distance is determined during the design phase, the average train frequency is 2 min. Suitable for use in areas where it is up.
In this system, the interlocking system decides how fast the train will go and senses the position of the trains and tells the train to the point where it should stop.
Moving block automatic driving
As mentioned above, how close each train is to the front train is calculated and transmitted to the train according to the speed of the train, braking power and road condition. The location of each train is locked separately and the speed of each train is calculated separately. Due to the security level, signaling is provided redundantly through dual channel communication.