The game also features a robust transportation system based on Colossal Order’s previous Cities in Motion, allowing the player to plan out effective public transportation for the city to reduce traffic. Roads can be built straight or free-form and the grid used for zoning adapts to road shape; cities need not follow a grid plan. Roads of varying widths (up to major freeways) accommodate different traffic volumes, and variant road types (for example roads lined with trees) offer reduced noise pollution or increased property values in the surrounding area at an increased cost to the player. The road system can be augmented with various forms of public transportation such as buses and subway systems.
Modding, via the addition of user-generated content such as buildings or vehicles, is supported in Skylines through the Steam Workshop. The creation of an active content-generating community was stated as an explicit design goal. The game includes several premade terrains to build on, and also includes a map editor to allow users to create their own maps, including the use of real world geographic features. Mods are also available to affect gameplay; prepackaged mods include the ability to bypass the aforementioned population tier unlock system, unlimited funds, and a higher difficulty setting.