The term "turbolift" creates the misleading impression that there would be elevators like those of today's buildings going to the various bridges. Turbolifts are completely different from today's elevators, though, and more akin to the cab ranks and road networks leading to the front doors of said buildings.
There's little need for multiple shafts when a single shaft can accommodate dozens of lift cabs going whichever way. Also, a shaft can go whichever way, and be moved one meter to the right on Deck 3 at a moment's notice (just ask the Quartermaster for four 90 degree turn pieces, or two 20 degree ones for that matter).
That a single door to the versatile turbolift network might be a bottleneck is disproven in those episodes where two parties can jump to separate turbolifts through the same doors just seconds from each other (say, "Let That Be Your Last Battlefield"). Is it a vulnerable choke point in case of accident or battle damage? Doubtful - it's just a shaft, and would probably continue to serve in some emergency capacity even if the doors were blown away (or jammed, after which they needed to be blown away, and were).
Different shis having different numbers of turbolift stations on the bridge is probably mostly a matter of personal preferences: some skippers will come aboard, tell the dock crews to install two more Civilization Spying stations and ditch the Auxiliary Engineering console," and, oh, move that lift station two notches to starboard2, while others will order an extra lift station to be installed, "I don't care where". And will be told "Yes, Sir, be done in two hours".
Timo Saloniemi
