The World Expansion, the one all backers of this campaign are receiving for free with their pledge, is a special kind of expansion: it is the only one that can be mixed both with the core game and any other expansion (whereas you can only play with 1 thematic expansion at a time). It includes 2 kinds of components: additional Objective tiles and Special pawns.

New Objectives
The new Objectives included in the World Expansion work just like those included with the core game and are simply added to the roster of Objective you can choose from when selecting your 3 Objectives at the start of the game, which you must then place when a Placement token with a flag is revealed on the Station board and adds a new scoring condition for the end of the game. For example, the Observatory wants to be placed in a column or row that contains at least 6 tiles.

Special Pawns
Each Special pawn is associated to one of the main types (Cars, Trains, or Travelers; the Bus pawn is a special Car pawn, for example) and comes with specific rules that affect where you can place them and/or how many points they are worth when you place them. For example, the Mechanic is a special Traveler pawn that can be placed on a Train pinpoint, in addition to a regular Traveler pinpoint; additionally, if you do so, you gain 1 additional point.

To place a Special pawn, you need to wait for the Placement token of the corresponding type to come up, just like a regular pawn of the same kind, but with an additional limitation: you can place a Special pawn only if you have at least 2 pawns of the same kind already placed on your network (they don't need to be connected to each other or the Special pawn that you want to place, even though that is usually better for you in terms of score).

—description from the publisher