Lane Topology Model
The topology layers for the Lane Model provide information on the basic connectivity of lanes. The fundamental component is a Lane Group, which is comprised of:
- A pair of Lane Group Connectors that indicate the start and end of the Lane Group (the Lane Group's longitudinal extent).
- A pair of Lane Group Boundary Geometries that connects the ends of the Lane Group and defines the Lane Group's lateral extent.
- One or more Lane objects that indicate the connections, without a specific shape, from the starting Lane Group Connector to the ending Lane Group Connector. All lanes have their longitudinal extent for the entire Lane Group, and a lane cannot begin or end anywhere other than at a Lane Group Connector.
The following figure illustrates a simple road segment with three lanes, extending between two intersections.
Its representation in the Lane Topology Model appears as the following figure.
Lane Group Connectors
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 and the other as 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, and the other is the End Lane Group Connector.
Lane Group Boundaries
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 starts at the Start Lane Group Connector, and ends at the End Lane Group Connector. In the figures in this chapter, the Lane Group Boundaries are red lines with an arrow indicating the start-to-end orientation.
At the Lane Topology level, a Lane is 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 figures in this chapter, 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, HERE defines a Lane Group for the extent where the lane is in the process of forming or ending. HERE refers to that lane as being "in transition," which is an attribute of the Lane object.
Topology Change Example
The following figure illustrates a section of road where three lanes become four lanes. There are three Lane Groups: one with three lanes, the next with four lanes, of which one is In Transition, and the final, with four fully formed lanes.
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. Its orientation is right-to-left in this example. It contains three 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 four 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 four 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 the following figure, Lane Group Connector 6 is connected to two Lane Groups, 13 and 14.
Because of the directions of travel, there is no Lane Group between Lane Group Connectors 5 and 7, and no traffic flows between them. 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-ramp junctions, HERE has 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 the following 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.