Theory:Doctor Who television discontinuity and plot holes/Gridlock

THERE GIANT CRABS NOT INSECTS, they don't have wings and they can't fly!
 * Why didn't the Macra fly up and kill any people in cars not just in "The Fast Lane" but any where?
 * If the Face of Boe truly is Jack Harkness, it does not make sense for him to die, since he is immortal.
 * Harkness still ages, just at a much slower rate; assuming no further time travel, he's now over 5 billion years old. He also gave the last of his energy to open the motorway; this last energy could have been the energy that was keeping him alive. Also, on several occasions in both Doctor Who and Torchwood, Jack "died" and did not immediately revive until some time later. We don't know for certain if Boe really died. It is also possible that being over 5 billion years old has taken its toll on Jack, perhaps even destroying his Immortality eventually, the effects of the vortex and his luck could have 'run out' as said by Ianto in Children of Earth.
 * Furthermore, there's no guarantee that Jack was even telling the truth about his nickname. He could have learned by other means that the Doctor and friends were acquainted with the Face of Boe, and be playing an elaborate joke on them.
 * Jack isn't immortal, he is described as a 'fixed point in time': he survives until he can pass his message (You Are Not Alone) to the Doctor.


 * It seems rather silly that the automatic quarantine would let people into the motorway (surely letting the virus in), but not let them back out. What's more, wouldn't any of the later entries to the motorway have noticed that nobody ever came out, or even tried to get out through the entrance shafts.
 * The quarantine was to separate the lower city from the upper city, not the lower city from the motorway. The motorway was probably sealed to prevent the citizens of the lower city from realizing that they were trapped, as they knew they could leave at any time.


 * What happened to the Macra? Where did they go after the events of Gridlock?
 * When the motorway opened up, the gas keeping the macra alive would have spread away.