Lane Topology Model
The topology layers for the Lane Model provides information about the basic connectivity of lanes. The fundamental component is a Lane Group, which comprises:
- A pair of Lane Group Connectors indicates the start and end of the Lane Group (the Lane Group's longitudinal extent).
- A pair of Lane Group Boundary Geometries connects the ends of the Lane Group and defining the Lane Group's lateral extent.
- One or more Lane objects, indicating the connections (wihout specific shape) from the starting Lane Group Connector to the ending Lane Group Connector. All lanes will have their longitidunal extent for the entire Lane Group; a lane cannot begin or end other than at a Lane Group Connector.
Consider the simple road segment illustrated here: three lanes, extending between two intersections:
Its representation in the Lane Topology Model would look like this:
Lane Group Connectors
Format Reference: LaneGroupConnector
Each Lane Group Connector is a straight line, defined as a 2D polyline. One end of the Lane Group Connector line is arbitrarily designated as its Start; the other is its End. In the illustrations in this chapter and the Lane Geometry Model chapter, the Lane Group Connectors are light blue lines, with an arrow indicating the start-to-end orientation.
With respect to a particular Lane Group, one if its Lane Group Connectors is arbitrarily designated as the Start Lane Group Connector; the other is the End Lane Group Connector. Note that a Lane Group Connector that is the Start of a particular Lane Group could be the Start or End of the adjacent Lane Group. Within the Lane Group, every object shares the same orientation: from Start Lane Group Connector to End Lane Group Connector. This is unrelated to the travel direction(s) on the Lane Group.
Lane Group Boundaries
Format Reference: LineString2dOffset
Both ends of the Start Lane Group Connector are connected to the corresponding ends of the End Lane Group Connector with a Lane Group Boundary Geometry. This geometry is 2D, but takes its shape from the outer boundaries of the outer lanes as defined in the Lane Geometry Model for this Lane Group. The orientation of each Lane Group Boundary Geometry is starting at the Start Lane Group Connector and ending at the End Lane Group Connector. In the illustrations in this chapter, the Lane Group Boundaries are red lines, with an arrow indicating the start-to-end orientation.
Format Reference: Lane
At the Lane Topology level, a Lane is simply a pairing between the Start Lane Group Connector and the End Lane Group Connector, without any precise shape. The Lanes are presented in order, left to right from the perspective of the Start Lane Group Connector facing the End Lane Group Connector. In the illustrations in this chapter, the Lanes are broken blue lines, with an arrow indicating the start-to-end orientation.
Lanes within a Lane Group extend across the entire longitudinal span. When a lane is forming or ending along a road, we define a Lane Group for the extent where the lane is in the process of forming or ending. We refer to that as lane as being "in transition," which is an attribute of the Lane object.
Further Example - Topology Change
This illustrates a section of road where three lanes become four lanes. There are thus three Lane Groups: one with 3 lanes, the next with 4 lanes of which one is In Transition, and the next with 4 fully formed lanes.
The three Lane Groups look like this:
There are four Lane Group Connectors, labeled 1 thru 4:
- Lane Group 10 starts at Lane Group Connector 2 and ends at Lane Group Connector 1. Thus its orientation is right-to-left in this example. It contains 3 lanes.
- Lane Group 11 starts at Lane Group Connector 2 and ends an Lane Group Connector 3. Its orientation is left-to-right in this example. It contains 4 lanes, one of which (lane 4) is "In Transition."
- Lane Group 12 starts at Lane Group Connector 3 and ends an Lane Group Connector 4. Its orientation is also left-to-right in this example. It contains 4 lanes.
Lane Groups at Intersections:
At intersections, there is a Lane Group defined between each incoming Lane Group and each appropriate outgoing Lane Group.
Lanes from a particular starting Lane Group Connector will not cross over one another.
At a road intersection, Lane Group Connectors may engage more than one Lane Group on the same side. In this example, Lane Group Connector 6 is connected to two Lane Groups (13 and 14).
Note that because of the directions of travel, there is no Lane Group between Lane Group Connectors 5 and 7; no traffic flows between them. Note also that the digitizing direction of the Lane Groups may or may not be consistent with the direction(s) of travel on the Lane Group.
More-complex intersections may require more Lane Groups. In this 4-way intersection example, each incoming road connects to each outgoing road, so there are six Lane Groups:
Lane Groups at On- and Off-ramp Topologies
At on- and off-ramps junctions, we have lane groups for the main road and for the lane(s) going to or from the ramp. They will have a Lane Group Connector in common. These examples are described as off-ramps, with traffic flowing from left to right, but the topology for on-ramps is identical.
In this topology, the ramp lane forms as it begins to separate from the main road: Lane 1 in Lane Group 22 overlaps Lane 4 in Lane Group 21. (Lane 1 of Lane Group 21 and Lane 2 of Lane Group 22 are Shoulders.)
Often, the lane leading into the ramp is fully formed before it begins to separate from the main road: Lane 1 in Lane Group 24 is adjacent to (not overlapping) Lane 3 in Lane Group 23. (Lane 1 of Lane Group 23 and Lane 2 of Lane Group 24 are Shoulders.)
Format Reference: LaneTopologyLayerTile
It is not uncommon for Lane Groups to straddle one or more delivery tiles. All the components of a given Lane Group, possibly with the exception of the Ending Lane Group Connector, will be provided in the same tile. The location of the Start of the Start Lane Group Connector will determine the tile to which the entire Lane Group belongs. If the Ending Lane Group Connector is in a different tile, we will provide a cross-reference to that Lane Group Connector including its tile ID.
Using our example from above, this will illustrate how Lane Groups are assigned to tiles:
Lane Group 10 starts at Lane Group Connector 2. Since the start of Lane Group Connector 2 is in tile 102221303020103, this Lane Group is published in that tile. Lane Group 10's Ending Lane Group Connector (Lane Group Connector 1) is in tile 102221303020102.
Lane Group 11 also starts at Lane Group Connector 2, so this Lane Group is published in tile 102221303020103. Lane Group 11's Ending Lane Group Connector (Lane Group Connector 3) belongs to tile 102221303020121.
Lane Group 12 starts at Lane Group Connector 3. Since the start of Lane Group Connector 3 is in tile 102221303020121, this Lane Group is published in that tile. Lane Group 12's ending Lane Group Connector (Lane Group Connector 4) belongs to tile 102221303020103.
More discussion on tiling is found in the section: Map Tiling