This accident seems to have been caused by human error. Moreover, (from the news) the working arrangements and procedures seem to be such that in the event of a controller (or driver) making a mistake there was no automatic failsafe protection in place to stop the Renfe train.
An automatic failsafe mechanism should be installed to stop/cut the power to the moving train in situations like this, it should work irrespective of any instructions or actions by the controller or the driver.
When safety parameters deemed the Renefe train to be travelling too fast and too close to the Iryo one it should have stopped automatically. Such safety measures aren't rocket science but straightforward engineering, (interlocks, etc.). Over the years there have been too many accidents in situations such as this for such equipment not to be installed.
For a moment I visualized myself in that busy control room and easily making that mistake even though I'd made the correct decision hundreds of times previously. Not only are 69 lost lives a terrible tragedy but the life of the person who made this momentary slip has been ruined forever.
It should not have been allowed to happen. It's worth remembering that Westinghouse brake systems (which are well over a century old) automatically default to on (stop) when there's a fault, and the high speed (now decades old) Shinkansen has very sophisticated stopping mechanisms and has never had a major crash. The question is why such safety measures weren't installed here.
Fundamentally I don't know what the cause is, because there is no full safety report yet, but I doubt that it was a driver error alone, which is what automatic braking systems at signals are actually targeting.
There are situations where the dispatcher needs to instruct the driver to ignore the road signals and hence also ignore the automatic enforcement of the signals. It shouldn't happen to often, but the real world is always more messy.
Some were installed. But what wasn’t there was the old mechanical ones that cannot be overridden, like ATS that blows the air if you pass a red signal.
https://en.wikipedia.org/wiki/Automatic_train_stop
Any failsafe that can be bypassed manually is just a deferral to humans and eventually will result in disaster.