What are the passenger bonus numbers?

When playing mini-metro at what passenger numbers do you get bonus items? I am trying to figure out how I can plan ahead and ect and this information could be extremely useful.

To summarize some of the other answers and comments:

• Normal: You receive the bonus at the end of each In-Game Week
  (after Sunday night is over, as shown on the clock in the upper-right corner)

• Endless: You receive the bonus when you reach an Efficiency Milestone
  (maintaining a certain number of passengers transported in a single day)

• Extreme: (the bonus is the same as Normal mode)

A more complete explanation of each mode has already been written up in this excellent Q&A:
What are the differences between the game modes?

It's not the numbers of passengers. You get the items with the In-Game Week system. You can see the progression of the week in the upper right corner. at the begining of each week, you get to choose a bonus Item.