I would think there would be at least 20 engineers, politicians, managers, etc. for the maiden voyage.
If the train slowed to 18 to cross the bridge, but then the rear engine kicked in erroneously too soon and pushed it back up to 79, the ‘speeding’ eyewitnesses are describing?
The rear engine pushing would explain the accordian effect. It would also explain how all those cars stopped without a massive pile-up.