How ASFA, the Spanish train safety system, works

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Excessive speeds were responsible for last week’s deadly train crash that killed 79 people, data taken from the “black boxes” has confirmed, but some reports say the tragic accident might have been prevented with better use of existing safety systems.

Spain uses two train safety systems: the ERTMS, or European Rail Traffic Management System, and the Spanish ASFA, or Aviso de Señales y Frenado Automático, a system of warning signals and automatic braking system. The ERTMS is more sophisticated than the AFSA. It employs wireless technology to constantly monitor train operations and can override a train driver’s actions to control the speed of a train. ERTMS is implemented on sections of train tracks that carry high-speed trains.

Some parts of Spain’s train network still use the older AFSA system. It relies on a series of beacons, or balises, which transmit train traffic information to computers on the train. These beacons work in conjunction with a system of traffic lights, as well as alerts on the train driver’s control deck.

When a train operating on the AFSA system is running at a safe speed for that particular section of the track, as determined by the information transmitted by the beacons, a green traffic light will appear, indicating to the driver that it is safe to continue. A yellow light will signal if the train is going too fast, and in response, the driver must respond to the system by sending confirmation of having received the alert, and by reducing train speed. If the driver fails to respond or slow the train, the next traffic light will be red, and the train will be instructed to slow down automatically, according to an article published by Spanish publication Publico.

The section of the train where the ill-fated Spanish crash took place operates on the ASFA system. However, not long before the curve is a space where systems transition from ERTMS to ASFA. Investigators are inspecting this section for additional clues to explain why the train was allowed to reach such high speeds, New Scientist reported.

Publico reports that the area just before the curve was not adequately equipped with enough beacons and had just two been implemented before the bend, the ASFA system would have intervened in time to prevent the accident.