I read on another article that there was such a system in place. Too early to say for sure what happened "the LZB signalling system, which automatically halts a train if the line ahead is occupied, had gone down at about 8.30am local time due to a computer malfunction. As a result, an estimated six trains had been halted along a stretch of around 63km" https://www.theguardian.com/world/2026/oct/28/spain-train-crash-high-speed-toledo