We don't really know what her motivations were. Right now we only know what the results are. Drivers need to take very seriously a crossing arm.

We don't know why the driver made the decision to cross. It appears that everything was working properly. Again, that's all under investigation.

We don't know why the individuals were on the tracks.

She drove around the crossing gates, apparently. The gates were down and everything was functioning as it was supposed to.