I definately agree with HyuugaNeji.... those two was definately
high on Alocohol or perhaps other stimulants.
There is sure many easier way to commit suicide... and I reckon
to suicide this way take alot alot of courage, think about the
Kamikaze Pilots in WW2....
From a psychological point of view, it is a very tought way to
suicide.
And the fact is both are being affected. Cos it takes alot of
psycho for one to influence the other to suicide in such a violent
way.
Hence, there could be many many possiblities....
but definately, they must be so high on alcohol and
other stimulants, that they will were not reacting normally... and
not sober enough to see the train and get away from it
which every animal survival instinct will be to escape from
it