Roman Pearce: You know, I think I make a better special agent than you ever did.
Brian O'Conner: I guess that depends on how you define 'special'.
Throughout the entire chase scene at the end, the vault creates sparks on the road. Yet when they get to the bridge, no sparks appear. This cannot be due to the vault being empty at this point, as the vault itself is 10 tonnes, as mentioned earlier in the film.