Result: train_id is unique per day only, but identifies the same train across days

=item $result->train_id

Numeric ID of this train. Seems to be unique for a year and trackable across

stations.

Numeric ID of this train, trackable across stations and days. For instance, the

S 31128 (S1) to Solingen, starting in Dortmund on 19:23, has the ID

2404170432985554630 on each station it passes and (usually) on every day of the

year.  Note that it may change during the yearly itinerary update in december.

=item $result->train_no