I.up [美 əp, 英 ʌp]副up often appears as the second element of certain verb structures in English (back up, pick up, sit up, etc). For translations, see the relevant verb entry (back, pick, sit, etc).
In the meantime the police have learned the particulars of the hold-up from the frightened passengers and have started up the railroad tracks after the fleeing robbers.
The three participants who performed a hold-up are shown stating positive things about their experience, although it is unclear whether these were taped before or after the heist itself.