Processing Divided Roads

Divided roads are roads that consist of a physical barrier (median) with one-way travel lanes on both sides. They are also represented as two one-way roads (way objects) in OpenStreetMap, which causes problems when identifying intersections. The divided_process function in tpov_match.py, along with the process_divided list of parameters, control whether to include or exclude certain roads from being included in intersection identification.

Example of a Divided Road Intersection

The diagram below shows an example of a two-way road that separates into a divided road, which then intersects with another divided road at an angled T-junction. Travel directions are as follows (This diagram assumes right-hand traffic):

• Road 1 (East-West):

  • G -> H -> J -> K (Orange)

  • D -> C -> B -> A (Red)

• Road 2 (North-South):

  • P -> N -> M -> J -> F -> C (Blue -> Purple)

  • B -> E -> H -> L -> N -> P (Cyan -> Blue)

All further documentation will refer to the diagram below.

Example of a divided road intersection

process_divided Parameters

process_divided parameters are shared across all cases of divided road processing.

• angle - The maximum angle difference of the two sides of the divided road (e.g. GH to BA). If the angle difference is greater than this value, they will be treated as separate roads.

• length - The maximum distance between the two sides of the divided road (e.g. BEH or JFC). If the distance is greater than this value, they will be treated as separate roads.

• same_name - If True, the two sides of the divided road must have the same name to be considered the same road.

• apply_filter - If True, the exit_filter function (docs) will be applied to divided road processing. For example, this could mean that a four-way intersection with one side being a service road is treated as a T-junction.

• enabled_cases - A list of which cases (see below) are enabled. There are currently 4 cases.

Case 1: Ignore short spur which leads to the opposite side of the divided road

Travel path: G -> H -> J -> K

Sensical intersection representation:

Current	Left	Forward	Right	Direction
H		J	L	Forward

Purely logical representation:

Current	Left	Forward	Right	Direction
H		J	L	Forward
J	F	K		Forward

Case 1 ignores the spur JFC as it just leads to the opposite side of the divided road.

Parameters:

• angle: HJ to CB

• length: JFC

Case 2: Ignore exit to the opposite side of the divided road at a turn

Travel path: D -> C -> B -> E -> H -> L

Sensical intersection representation:

Current	Left	Forward	Right	Direction
B	E	A		Left

Purely logical representation:

Current	Left	Forward	Right	Direction
B	E	A		Left
H	J	L		Forward

Case 2 ignores the opposite side of the divided road (HJ).

Parameters:

• angle: CB to HJ

• length: BEH

Case 3: Add exit for a far turn (left in right-hand traffic) onto a divided road at a T-junction

Travel path: M -> J -> F -> C -> B -> A

Sensical intersection representation:

Current	Left	Forward	Right	Direction
F		J	K	Forward
C	B			Left

Purely logical representation:

Current	Left	Forward	Right	Direction
F		J	K	Forward

Case 3 adds a row to show that a left turn was made, even though there is no intersection at C due to only one possible direction.

Parameters:

• Angles (Both have to be satisfied):

  • prev_angle: MJ to JF

  • angle: JK to CB

• length: JFC

Case 4: Ignore “intersection” when a divided road merges back into a two-way road

Travel path: H -> L -> N -> P

Sensical intersection representation:

Current	Left	Forward	Right	Direction

Purely logical representation:

Current	Left	Forward	Right	Direction
N	M	P		Forward

Case 4 ignores segment NM as it is a U-turn back to the same road.

Parameters:

• angle: HL to MJ (Not currently used)

• Lengths (Both have to be satisfied):

  • dist: LM

  • dist2: HJ