Media playback is unsupported on your device

Spain train crash: How did the accident happen?

25 July 2013 Last updated at 16:36 BST

An investigation is underway in Spain into the country's worst train crash since 1944 - killing at least 78 people.

The train derailed just before arriving in Santiago di Compostella - sending eight carriages crashing into each other.

The rail firm says there were no technical problems with the train and that it had been inspected just hours earlier. It is reported the driver is now under formal investigation.

It is thought the train was going much faster than the speed limit of 80 kilometres an hour.

Jeremy Ackland, a rail expert from the Institute of Engineering and Technology, explains how train speed controls work.

Copyright © 2015 BBC. The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.