incredibly tacky of me to even wonder about this, but I can't help it. How could the truck get there and get going so fast? I mean, I'm thinking of Baltimore's fireworks, for example. Bollards and concrete trashcans to keep trucks off promenade and the streets are always gridlocked around the fireworks. Not so elsewhere?
From a comment on MetaFilter by someone who used to live in Nice, I get the impression that any roadblocks are just temporary for the fireworks. Get past them... https://www.metafilter.com/160976/Bastille-Day-tragedy-in-Nic... ‎- Galen Charlton