The following describes the supported methods for building Road Corridors, intersections, knuckles (sharp bends) and cul-de-sacs.
Road Corridors
Corridors can be created using standard alignments and assemblies.
Allsite.ai does not currently support custom combined sub-assemblies. Support may be added in future.
Alignments
Road Centerline Alignments are drawn as normal.
Alignments drawn past the end of a cul-de-sac or T-intersection can cause issues, so ensure they are trimmed to the road region end.
Intersections
An Intersection represents the area where two or more roads meet and connect.
Intersections can be created using the Civil 3D Intersection Wizard or manually, provided the same geometric and profile principles are followed.
Definition and Requirements
For the plugin to recognize and process intersections correctly, the following requirements must be met:
Creation Method:
Intersections can be created either with the Intersection Wizard or manually, as long as the same design principles are observed:Offset Alignments
Offset Curb Returns
Create intersection with dynamic profiles.
Curb Return Subassemblies:
When creating intersections manually, use the “Gutter Edge” insertion point for the curb-return subassemblies (Default on C3d).
Feature Lines are not supported to define curb returns or targets.
Optional: Before creating intersections, creating preliminary design profiles will help avoiding setting Alignments profiles in the intersection settings.
Curb returns must have a 'lane' subassembly, this extends mesh lines towards the target alignment. In the future support will be added for this type of curb return / cul-de-sac.
Profiles
When the corridor is created, use the Existing surface to define the corridor profile, a design profile will added by Level AI automatically. Alternatively you can add a placeholder design profile and apply styling - this design profile will be updated and styling retained after a Level AI run. If you create the design profiles prior to creating intersections the intersection regions can be set up to target the design profile. If letting Level AI automatically create the design profile, you will need to update the intersection regions following the first run.
Allsite does not support secondary road profile rules. The extra PVI points will be automatically removed from profiles when Level AI brings in results. This is because Level AI is automatically grading the roads at these tie-ins between roads and the extra points added can mess with the design.
Cul-de-Sacs
A Cul-de-Sac represents a terminal road bulb or turning area at the end of a road.
It typically consists of a single alignment defining the bulb geometry and a main road alignment (centerline) that terminates at the bulb’s center.
Definition and Requirements
To be supported by the plugin, cul-de-sacs must comply with the following requirements:
Location: Found at the end of a road or a closed terminal section.
Alignment Definition:
The Cul-de-Sac should be represented by one centerline alignment defining the tangential bulb arc or circular end.
The Main Road Alignment (used as target) must end/start at the center of the cul-de-sac.
Alignment Continuity: The Cul-de-Sac alignment should connect and align or overlap tangentially with its adjacent region, depending on the curb return subassembly used (insertion point: Curb Back or Gutter Edge).
Region: A Cul-de-Sac will have one baseline and region
Region Association:
The Cul-de-Sac Alignment should start and end at the same station of the Main Road Alignment
The same centerline alignment is shared between the adjacent region (as baseline) and the cul-de-sac region (as Target).
Target:
The target must be set to the Main Road Alignment and be curved to the center.
Other supported geometry: Sided Cul-de-Sac
Note: Using the Road Main alignment as cul-de-sac baseline is not supported.
Knuckles / Bulbs
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.
Note: curved alignments through knuckle corners are not currently supported.
Note: using road main alignments as baselines for knuckles is not supported yet.
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:
