I don't know what your problem is. Why it's as clear as mud!
The basic time 1 worker takes to do a job is determined by: Terrain Type, Nationality (i.e. Industrious or not), Government type (I think Democracy is the fastest), and the discovery of Replaceable Parts (which speeds the worker up).
You can use more than one worker to hurry an improvement. For instance under one government type (Monarchy?) it takes three turns for one worker to build a road on grassland. Two workers take 1/2 as long ROUNDED UP to the nearest whole number = 1 1/2 rounded up to 2 turns. Three workers take 1/3 as long = 1 turn.
If you don't know how long a task will take, then send 1 of your workers to that square. If you place the mouse pointer over the screen icon for the task you want, then it will tell you how many turns it will take.
Everything clear so far? Good! Moving right along. :crazyeyes
Now, Captured Foreign Workers will only work as fast as their own Nationality and (if I recall) that civ's Government type allows (I don't know how that would work if you have destroyed that worker's civilization).
For instance, if you are France (Industrious) with Democracy and have discovered Replaceable Parts then 1 worker can build a road in 1 turn.
If you have captured a worker from the Russians (Not Industrious) and they are under Despotism, then it will take the Russian worker longer to build the road. It only gets super confusing when you have a stack of French workers with Russian, American and Zulu workers. This is even more confusing since the last patch because that captured Russian worker will now show up as a Worker (French) in some cases.
Anyway, its only critical when moving into an unimproved square. I try to send the minimum number needed to build a road in one turn.
Otherwise I ignore all this other stuff and just keep sending workers until the job is done.
Now aren't you glad you asked?
