When a Polish train driver noticed a truck blocking part of the track ahead of his vehicle, he didn't have time to bring the carriages to a stop before impact. So he used the three seconds he had to sprint through the train, warning passengers of the impact.
The BBC reports that the impact occurred while the train was travelling at 100km/h. It's thought that nobody was badly injured, which is surely in part down to his warning the passengers in the front section of the train that the impact was about to occur, giving them time to hunker down for protection. What an amazing guy.