NetInfo objects will be paired with new ExtNetInfo objects to provide extended information. Initially this will be to group car lanes based on medians and directionality. The ExtNetInfo objects will be generated on first request, and stored in a static instance of a backported ConcurrentDictionary keyed on the NetInfo reference.

Each car lane will be assigned a set of flags:

public enum LaneGroupFlags {
    Standard = 1 << 0,
    Express = 1 << 1,
    DisplacedInner = 1 << 2,
    DisplacedOuter = 1 << 3,
    Forward = 1 << 4,
    Backward = 1 << 5,
}

Forward and Backward do not directly map to the vanilla lane direction. They identify a lane group's prevailing vehicle direction, and may not match a specific lane's direction in some cases.

The lanes are organized in these steps:

1. Apply Forward/Backward flags to car lanes.
2. Identify displaced lanes based on the rules described below, and apply the DisplacedInner and DisplacedOuter flags.
3. Identify medians based on the rules described below.
4. For all lanes that are neither DisplacedInner nor DisplacedOuter:
   1. If a lane is inside a median in relation to other lanes in the same direction, apply the Express flag.
   2. For all other lanes, apply the Standard flag.

Once this is done, a collection of lane group objects are created and stored in the ExtNetInfo object. Each lane group contains a collection of car lanes having the same LaneGroupFlags. Note there will always be one lane group for one-way roads, and at least two lane groups for two-way roads.

public class LaneGroupInfo {

    public LaneGroupFlags m_flags;

    /// <summary>Aggregate of all lane types found in this group.</summary>
    public NetInfo.LaneType m_laneType;

    /// <summary>Aggregate of all vehicle types found in this group.</summary>
    public VehicleInfo.VehicleType m_vehicleType;

    /// <summary>lane indices, sorted by position</summary>
    public int[] m_lanes;
}

Displaced Lanes

"Left" and "right" here assuming you are looking down a segment from its starting end, so that negative positions are on the left and positive positions are on the right.

Note that when the road has a simple configuration with forward lanes on the left and backward lanes on the right, these are not considered displaced lanes. They are inverted, but not displaced.

Forward Lanes

1. A forward lane is DisplacedOuter if all of the following conditions are true:
   1. There are no backward lanes to its left.
   2. There are backward lanes to its right.
   3. There are more forward lanes on the other side of the backward lanes.
2. A forward lane is DisplacedInner if all of the following conditions are true:
   1. There are backward lanes both to its left and to its right.
   2. There are more forward lanes on the other side of the backward lanes to the right.

Backward Lanes

Displaced backward lanes are identified by reversing the rules for displaced forward lanes.

Medians

A non-car lane is considered a Median if either of these criteria are met:

1. The lane is at a higher vertical offset than that of the car lanes around it, but the difference does not exceed 3 meters. (The 3-meter limit will prevent false positives on certain types of mass transit.)
2. The gap between the nearest car lanes on either side is at least as wide as the widest of those lanes.

In addition, a Median lane cannot overlap any car lane.