Q/A: All vehicles use the same lane / Vehicles cannot reach certain locations

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Problem description

Some users report problems with vehicles not using all free available lanes.

Possible causes

The sections below describe possible reasons for this behavior and how to fix the underlying problem. The topics are roughly sorted by how easily the underlying issue can be fixed.

Advanced Vehicle AI is disabled

When the Advanced Vehicle AI is disabled, the base game algorithm controls lane selection, which some player may find suboptimal.

Solution: Activate the Advanced Vehicle AI (see Options → Advanced Vehicle AI.

Advanced Vehicle AI has not been active long enough

After enabling the Advanced Vehicle AI it may take up to ten minutes until you see visible changes. Since the AI modifies path-finding, it affects newly spawned vehicles only. The AI does not control vehicles that are already en route.

Solution: Wait for up to ten minutes until all vehicles passing the road segment used the Advanced Vehicle AI to calculate their routes.

Vehicle restrictions were set up

Vehicle restrictions are there to ban certain types of vehicles from using certain road segments. If you do not provide alternative routes, specific buildings or even whole regions on your map end up being completely inaccessible for motorized traffic.

Solution: Make sure to provide alternative routes when setting up vehicle restrictions.

Faulty lane arrow/connection configurations

This problem often comes hand-in-hand with the Insufficient lane changing opportunities issue.

Faulty lane connections or missing lane arrows may cause lanes to become unreachable for vehicles. The set of images below illustrate a situation where this is the case. This real case was originally submitted in the discussion section of TM:PE's workshop page.

A faulty lane connection causes the rightmost lane of the 3-lane one-way to become unreachable.
  1. The first image shows the faulty lane connection configuration. At the right side you can see that the setup lane connections do not allow vehicles coming from the 3-lane highway to use the rightmost lane of the 3-lane one-way street.
  2. The second image shows how vehicles are allowed to move. Since access to the rightmost lane is blocked the route highlighted with a purple arrow will never be taken by vehicles originating from the highway.
  3. The third image shows how the lane configuration can be fixed. Two modifications were made (where only the first is really important but the latter yields even better results):
    1. A lane connection was added that connects the middle lane of the highway with the rightmost lane of the 3-lane one-way street. Vehicles are now able to use the lane in question and thus the purple route in the second image is now accessible.
    2. Lane arrows were changed such that the rightmost lane of all the 3-lane one-way road segments only allow vehicles to turn right.
  4. The fourth image shows how vehicles are allowed to move after the modifications were performed. TM:PE's junction routing algorithm is now able to spread traffic to the highway lanes more evenly since the two leftmost lanes of the 3-lane highway segment now both feed at least one of the side streets.

As you can see, having healthy lane arrow and connection configurations is vital.

Solution: Fix your lane connections and lane arrows in a way that allows vehicles to use the lanes in question.

In the example above you may have wondered why vehicles are not able to switch lanes between the junctions. This topic is explained in the next section.

Insufficient lane changing opportunities

An important aspect regarding lane changing is to understand how it works behind the scenes: Roads consists of segments and (mostly invisible) nodes. By opening up the lane connector tool you can see these nodes (they are visualized for you as grey circles). The game is designed in a way that lane changing can only take place at nodes.

The lane connector visualizes potential lane changing points (nodes) as grey circles.

As you may notice not only junctions are potential lane changing points: Even continuous roads (like the 6-lane highway on the picture) possess nodes that act as points where lane changes may happen. Problems with vehicles using only a single lane can occur if you lay out a grid-like road network consisting only of short road segments like on the following image.

If junctions are close together no lane changing points are inserted in between.

Since the game does not add nodes to short road segments vehicles are forced to choose their lane early. The next picture shows a situation where this exact problem occurs.

Vehicles are using only one lane of the 3-lane road on the lower half of the picture.
The lane connector tool shows that no lane changing points are present between the junctions.

In the screenshots above you can see that all vehicles are eventually using only the outermost lane because they need to get from the 6-lane main road to one of the 2-lane side streets. Note that the Advanced Vehicle AI and Dynamic Lane Selection still try to maximize lane usage where possible: Vehicles approaching from the highway on the upper half of the picture use all available lanes (but tend to be on the "right" lane on time). The yellow arrows on the image indicate where some of the approaching cars change lanes to finally reach their target lane.

One way to tackle the problem is to create artificial nodes between junctions. The following screenshots show how it can be done.

1st step
2nd step
3rd step
4th step
  1. Build a road such that it connects to the center of the problematic road segment.
  2. Repeat the first step for every road segment in question.
  3. Remove the roads that you have just built. Even after they have been demolished, nodes that have been created stay intact.
  4. Vehicles will start to use more lanes (but wait: see what happens next to the yellow arrows).

Be reminded that creating artificial nodes alone will not solve the underlying problem though. As you can see in the last picture, even after creating artificial lane changing points cars finally need to get to the outermost lane in order to turn right. In this showcase upgrading the side streets to 4-lane roads (2 lanes for each direction) and potentially modifying lane arrows on the main street such that two lanes are available for turning would be a far more efficient way to solve the issue.

Solution: Make sure that the road segments in question occupy enough nodes. Check the overall number of available (turning) lanes as well as the lane arrow and connection configuration.

Required background knowledge

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