Allsite builds a full Civil 3D corridor for you from your road centrelines: the roads, the intersections and curb returns between them, and the cul-de-sacs and knuckles, each sized from the road's own Allsite data. The result is an ordinary Civil 3D corridor that Level AI grades like any other, and you can review and edit it with the usual Civil 3D tools.
This replaces the earlier basic corridors and Allsite simple road corridors workflows. If you would rather build your corridor by hand, see Creating Roading Network (full corridors).
Getting started
Draw your road centrelines as polylines or alignments. Where one road meets another, end it on the other road's centreline (a T), or run the two through each other (a crossing).
Select them all and convert them to Allsite Road (Simple Corridor) objects. Polylines are converted to alignments.
Set the layout parameters on each road — distance to back of curb, intersection radius, cul-de-sac and knuckle radii and so on. See Road Layout Settings below.
Tip: use the QSELECTPROPERTYSET command to select roads of one type and set their parameters together, for example every LOCAL road's intersection radius.
Set the longitudinal grade information, as for full road corridors.
Make sure the drawing has the road section you want to use. See Assemblies below.
On the Allsite.ai ribbon, in the Layout Assist panel, click Generate Road Corridor.
Confirm. The question names the corridor it will build into and what it will clear first. If any road still needs a profile view or a design profile, the same question says so; answer Yes and pick a base point for the profile views when asked.
When the run finishes, the Allsite AI Assistant shows what was built: the corridor, how many roads were built and how many junctions, and any errors or warnings. The same errors and warnings are in Panorama.
What Generate Road Corridor builds
One corridor, named Corridor - Allsite, with a baseline on every road. It is placed on your C-ROAD-CORR layer if the drawing has one, otherwise on AS-CORRIDOR.
The roads, each built with your road section at the road's own Distance to Back of Curb. A copy of the assembly is made for each width the roads use, named <assembly> @ <width>.
Intersections and curb returns at every T and crossing, at the Intersection Radius. Where two roads have different radii, the smaller one is used. A radius of zero gives a square corner.
Cul-de-sacs and knuckles, as feature lines, where the road's settings ask for them.
Levels. The curb returns, cul-de-sacs and knuckles are levelled from the roads' design profiles, and the corridor is rebuilt.
Running it again
Generate Road Corridor always builds from scratch. Run it again after you move a centreline or change a width or radius. First it clears every baseline and region on the corridor it builds into, and erases the offset alignments, curb returns, cul-de-sacs and knuckles it created on an earlier run. Your own alignments, feature lines and other corridors are kept.
Baselines you have added by hand to the Corridor - Allsite corridor are removed on the next run. Keep hand-built roads in a corridor of their own.
Generate Road Corridor stops before changing anything if a road crosses itself or closes on itself into a loop, and names the place. Split that centreline into separate roads and run it again.
After editing a design profile: Rebuild Corridor
If you have only changed a road's design profile, you do not need to build the corridor again. Click Rebuild Corridor, next to Generate Road Corridor. It re-levels the curb returns, cul-de-sacs, knuckles and offset alignments from the roads' profiles, then rebuilds the corridors so they model the new levels. Nothing is created, moved or erased, so your hand edits survive.
Rebuild Corridor works on any Civil 3D corridor, including ones you built yourself, and does not need an Allsite sign-in or project.
Rebuild Corridor does not change plan geometry. If you have moved an alignment or changed a carriageway width, the curb returns no longer meet the road edges. Run Generate Road Corridor instead, or adjust the curb returns by hand.
Then generate parcels, driveways and potential grade breaks
Once the corridor is built, the Generate Others dropdown next to it generates the rest of the layout against the corridor's road edges, one output at a time:
Generate Parcels lays out lots in the space the roads leave.
Generate Driveways adds a driveway to each lot. Set each lot's Normal Parcel Subtype first: a lot left at None gets no driveway.
Generate Potential Grade Breaks adds candidate retaining walls along the lot lines for you to review and promote.
Road Layout Settings
Setting | Description |
Distance to back of curb (left and right of centre) | Distance from the road centreline to the back of curb, left and right of centre. The road is built to exactly this width; a road without it is skipped and named in the errors. Leave the right blank and both sides use the left value. |
Intersection radius | Radius of the curb returns where this road meets another, measured to the back of curb. Where two roads meet, the smaller of their two radii is used. Zero gives a square corner. Also used for the knuckle and cul-de-sac curb returns on any road whose exit radius is left blank. |
Crown maintained rank | Which road keeps its crown through an intersection. 1 is the highest priority, larger numbers are lower, and 0 (the default) is the lowest. See Crowns at intersections. |
Crossfall centre to curb (left and right) | The fall from the centreline to the curb, used to level the edges of the road at intersections. |
Cul-de-sac radius | Radius of the cul-de-sac bulb at the end of this road, measured to the back of curb — not to the right-of-way. Set to zero for no cul-de-sac. The knuckle / cul-de-sac exit radius is used for the curb returns where the bulb meets the road. A road end that sits on the earthworks boundary runs off site and gets no cul-de-sac. |
Cul-de-sac type | Where the bulb sits relative to the end of the centreline. Centre — a symmetric head on the end of the road. Left / Right — the road runs straight through and the bulb is offset to that side. None — no cul-de-sac. |
Knuckle outer radius | Radius of the outer edge of the knuckle bulb at a sharp bend in this road, measured to the back of curb. Leave blank or zero for no knuckles. See Knuckles at sharp corners. |
Knuckle / cul-de-sac exit radius | Radius of the curb returns where the straight road curb meets a cul-de-sac head or a knuckle, measured to the back of curb. One value covers both. Leave it blank, or zero, to use this road's own intersection radius. |
Knuckle inner radius | Radius of the curb on the inside of a knuckle, measured to the back of curb. Leave it at 0 to use the knuckle / cul-de-sac exit radius. Set on the road in Civil 3D; it is not in the Road layout parameters table. |
Knuckle centre offset | Moves the centre of the knuckle bulb from where the centrelines meet into the inside of the corner, so the bulb bulges less past the corner. 0 (the default) keeps it centred on the corner. Set on the road in Civil 3D; it is not in the Road layout parameters table. |
Knuckle inner / outer extra elevation points, cul-de-sac extra elevation points | How many extra elevation points are added along the inner or outer edge of a knuckle, or along a cul-de-sac's edge, spread evenly between its vertices. The default is 1; 0 means vertices only. Add more where an edge needs closer level control. |
Width centre to ROW (left and right) | Width of the right-of-way from the centreline, left and right. Must be greater than the distance to back of curb. Used by Generate Parcels, not by the corridor. |
New Road (Simple Corridor) objects take their layout dimensions from the Road layout parameters table in your project's Layout Assist settings. The row is matched on the road's Road Category, and the LOCAL row is used for any category without a row of its own. You can override any value on an individual road afterwards.
Crowns at intersections
At an intersection, one road can keep its crown running through while the other road's crown stops at the junction. Crown maintained rank decides which:
At a crossing, the road with the higher priority keeps its crown. Equal ranks keep both crowns.
At a T, the through road keeps its crown alone only when it outranks the road ending on it. Otherwise both crowns are kept.
Remember that 1 is the highest priority. If every road is left at the default of 0, the confirmation says so before anything is built, because every junction then keeps both crowns.
Knuckles at sharp corners
You do not draw the knuckle. Draw the road centreline through the corner as you normally would, set Knuckle outer radius on the road, and Generate Road Corridor widens the corner.
A knuckle is added where all of the following are true:
The centreline turns through less than 150° — either at a vertex inside one centreline, or where two centrelines meet end to end.
The road has a knuckle outer radius greater than zero. Where two roads share the corner, the larger of their two radii is used.
The corner is clear of a cul-de-sac — a bend just before a turning head keeps the head alone.
Where three or more roads meet, the corner is an intersection rather than a bend and takes the intersection radius instead. The curb returns out of a knuckle use the knuckle / cul-de-sac exit radius.
Assemblies
Generate Road Corridor uses the road sections already in your drawing, recognised by what they are made of rather than by their names, so you can use your own assemblies and subassembly library:
Road section: an assembly with a lane and then a curb on each side, laid out from the crown. Sections with a median or a second carriageway beyond the curb (boulevards) are not used. If the drawing has none, Civil 3D's Primary Road Full Section is imported.
Half and part sections for the approaches to a T are made from your road section, so they carry the same curb.
Curb return fillet: the fillet assembly in the drawing whose curb best matches your road section's, and its mirror for the other hand. If the drawing has none, Civil 3D's Curb Return Fillets is imported.
If the closest fillet does not match the road's curb exactly, a warning says what differs. Assemblies the run adds are placed to the left of the design; assemblies already in the drawing are never moved or changed.
Curbs outside the corridor (carparks)
For a carpark or anywhere else outside the road corridor, you can still draw curbs by hand and convert them to Road Modifier objects. Set the direction of the modifier; the symbology updates to show the gutter side.
Set the Insertion Point to say which point of the curb cross section the line you drew represents. The options are the Civil 3D subassembly point codes:
BACK CURB (default) — back of curb, point code Back_Curb
TOP CURB — face of curb at the top, point code Top_Curb
FLOWLINE GUTTER — gutter invert / lip, point code Flowline_Gutter
FLANGE — outer edge of the gutter where it meets the carriageway, point code Flange
The rest of the cross section is placed relative to that point, so the same sub assembly can be used whichever line you have drawn. The sub assembly needs the matching point code on its surface shape; if it does not have one, the cross section is placed from the back of curb.
