Factual error: In order to detach wagons from the train you have to do more than simply taking off an unsecured lid in the ground and ripping out some cables.
Factual error: When Frank's Audi plunges into the deep body of water underneath the bridge, he succeeds in using the air from the tires to fill some empty bags in the trunk with air in order to send the car back up to the surface. In reality, the air in the tires would not be enough to keep it afloat, no matter where it's stored. The air in the tires will expand by a factor of something like 33, but that's still not a large enough volume of air to refloat the car.
Answer: Deactivating a complex bomb like that would have taken time, which Frank did not have and he was being monitored by high tech hardware.