Highway rules

From Traffic Manager: President Edition
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You may notice vast differences between in-game and real-life vehicle behavior on highways.

  1. In reality you may notice that cars only very rarely change multiple lanes at once on highways while multi-lane changes may happen quite frequently in Cities: Skylines (depending on the layout of your network).
  2. When exiting/entering a highway vehicles gradually switch to or come from a designated lane in real-life, whereas in-game vehicles arriving from a feeder road (e.g. a highway ramp) very often cross multiple lanes at once while entering the main highway.

In the real world almost every highway entry/exit is equipped with so called deceleration/acceleration lanes. They are needed in order to maintain a steady flow of traffic on the main highway and to ensure traffic safety by means of minimizing the danger of collisions between slow and fast moving vehicles:

  • Vehicles enter the highway via acceleration lanes in order to reach the highway target speed and
  • vehicles exit the highway via deceleration lanes in order to slow down and reach the target speed limit associated with the exit ramp (which is usually lower than the highway speed limit).
In an optimal scenario each incoming lane leads to exactly one outgoing lane.


You can enable or disable the feature by following these steps:

  1. Click on the gear icon in the upper right corner of your screen or press Escape.
  2. In the pause menu click on Options.
  3. In the left navigation pane, select Traffic Manager: President Edition.
  4. Switch to the Policies & Restrictions tab.
  5. Activate the checkbox labelled Enable highway specific lane merging/splitting rules.

Lane changing

While highway rules are activated lane changes must be performed incrementally, that means one-by-one (emergency vehicles on duty are excluded from this restriction).

Entries & exits

Vehicles are forced to stay on their lane when entering or exiting a highway. You can relax this restriction by using the Junction restrictions tool on the respecting highway interchange node(s): Activating the Lanechange.png Allow lane changes for vehicle going straight on feature enables vehicles to change lanes at either selected (using the tool) or all (see Options) highway interchanges and junctions.

Hints & remarks

  • In order for the feature to work optimally there should always exist exactly one outgoing lane for each incoming lane.
  • When you enable highway specific lane merging/splitting rules the lane arrow changer gets disabled for highway interchanges because the arrows are automatically set by the highway lane selection rule set. However, you may use the Lane connector tool to override highway rules at any location.
  • Due to performance considerations, enabling/disabling this setting always affects newly spawned vehicles only. The Customizations come into effect instantaneously setting (see Options) does not apply here.

See also

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