A Knuckle (or bulb) represents a sharp corner or tight curve in a road network, typically used to model the turning point between two connected alignments.
Knuckles can appear with or without a bulb (flared widening), but their geometric and targeting setup follow the same general rules.
Definition and Requirements
To be supported by the plugin, knuckles must comply with the following requirements:
Location: Positioned on a sharp curve of a road.
Curve Definition: The curved road must be defined by two independent connecting alignments (To be used as Targets).
Knuckle Definition: The knuckle itself must be represented by two alignments forming its outer and inner edges.
Alignment Continuity: Both knuckle alignments should connect and align tangentially with their adjacent regions, depending on the curb return subassembly used (insertion point: Curb Back or Gutter Edge).
Regions: A Knuckle will have a baseline and region per its respective alignment(Inner/Outer).
Targeting: Targets must be set to the centre of the road alignments. (See example image showing region and targets.)
Bulb/No-Bulb Cases: Both bulb and non-bulb cases are supported; the construction principle remains the same.
Curved alignments through knuckles are also supported.
Detailed Drawing Example
Before creating the knuckle, have your (separate) alignments intersecting. Decide on your curb type now, as it will affect the flow of operations. Allsite.ai currently supports Gutter Edge, or Back of Curb curbs.
To make them tangential, draw Polylines straight out from your chosen corridor line.
Repeat for the same side of the other corridor region. Don't draw too far as we want to place a curve.
Flatten your new polylines to remove any z values, then use the fillet tool to connect them with a curve.
Convert this curve to an alignment, add a surface profile, then repeat for the other side.
Next, create two basic assemblies labelled 'Left knuckle' and 'Right knuckle'.
In Tool Palettes, add a UrbanCurbGutterGeneral. Change your curb side (Left knuckle assembly means right side curb), and choose the insertion point based on how you constructed the corridor at the start.
In Tool Palettes, add in LaneSuperelevationAOR.
Repeat this assembly creation for the other side.
Add your previous two alignments as Baselines in Corridor Properties, randomly assigning your L / R assemblies.
In Corridor Properties, change the Target of both of these alignments to just the intersecting middle road alignments.
After rebuilding the corridor, if you notice a side looks odd, change the assembly for that alignment. Make sure to re-assign a target again, then rebuild the corridor one last time.
Click for detailed steps for creating a knuckle:
