On Wednesday, Istanbul-Konya high speed train and Adapazari-Pendik regional train had almost crashed head-to-head.

There are several questions about this accident, most of which will be clear after completion of investigation, where some of them can be answered by now. Here are some of them:

Did trains crash head to head?

The trains crashed head-on, but at a very low speed, more like a touch rather than crash. The HST was already stationary on the line where Ada Express (regional train) was stopped by use of the emergency brakes, as stated by news agencies. Light injuries may have occured during that emergency braking and slight collision.

Why two trains use same line on a 3-tracks-railway?

2 of 3 tracks of railway is for Marmaray suburban trains. 3rd line is being used by HSTs, regional trains and freight trains in both directions. Freight trains are running after midnight, however HSTs and other passenger trains which are running during daytime may come head-to-head.

Why Marmaray was not build with 4 tracks?

It’ll mean more security and capacity if there were 2 tracks for passenger trains. However the line goes through center of Istanbul, through huge and tall buildings. When Marmaray was built, the existing double track railway was renewed as 3-tracks by using the free space in sides. For 4th track, a lot of buildings should have demolished which would surely mean more time and more cost.

Is the line signalized?

Yes, both the 2 tracks which are used by Marmaray suburban trains, and the 3rd line which is used by all other trains are signalized. Marmaray tracks have CBTC where 3rd line has ETCS Level1 system.

Signalization in Turkish railways 2021

The map is published showing signalization of Turkish railway in operation and under construction.

What does having signalization mean?

With this signalling system, the control center can see which train is in which track. It also shows train drivers if the track is suitable to continue or not. With the help of systems in trains, signals can be read and train can be forced to stop when driver ignores stop signs.

Can it be fault of driver?

If signalization worked well, red light will be on for the driver of Ada Express which will enable stopping earlier. Even if he missed the light, control system of train would stop the train. So there’s a possibilty of signalization failure.

On the other hand, it seems driver of Ada Express had used the emergency brake to stop the train. Since train approached that point through a curve, driver possibily had acted fast and prevented a bigger accident.

Can it be signalization failure?

Since Ada Express was not stopped neither by driver nor system before, there’s a possibility of signalization failure. On the other hand, high speed train was waiting on main track (not at station nor a parking line). That may show that it was stopped either by driver or automaticly due to red signal sign. It’s not likely that signalization system works well in one direction and not in the other direction.

What else could have happened?

Another possibilty is that the train control system of Ada Express had failed and did not stop the train despite signals said “stop”. If signalling works well, this might be the main problem.

What’s next?

The investigation had started by Ministry of Transport, which will clarify the reasons of the accident and state the precautions to prevent similar ones.

Are trains safe?

Trains have several possibilities to minimize human-fault and have regular maintanance unlike cars and buses. However, railway is changing fast in Turkey, trains are getting faster, lines are getting busier. Management, drivers, maintanance and control systems must follow this fast change very closely, thus courses, procuderes must have been updated according to new needs. Each train crash ends up with not only unforgettable tragic memories, but also new precautions that prevent similar accidents.