Typical sections and corridors

This chapter shows how to turn a centerline and a design profile into a 3D road: first the typical section (an assembly), then the corridor that sweeps it along the alignment and daylights it to the ground. You'll be able to make a DPWH typical section in two clicks, change any lane, shoulder or slope, build and tune the corridor, and print slope stakes for the field.

How it fits together

A typical section is the road's cross section: lanes, shoulders (or curb, gutter and sidewalk), and the side slopes that run out to the ground. Terrace calls it an assembly. An assembly is made of subassemblies (parts): one part per lane, shoulder, curb or slope, each attached to the edge of the part inside it. The point where the assembly hangs from the centerline is its baseline point.

A corridor is the assembly swept along an alignment. At every section (every 10 m on tangents and 5 m on curves by default) Terrace places the assembly at the centerline's position and the design profile's elevation, tilts the lanes to the alignment's superelevation, and runs the side slopes until they meet the existing ground. The line where a side slope meets the ground is the daylight line. Joining the same point from section to section gives the corridor's feature lines (edge of travelled way, edge of shoulder, daylight…), and joining the top and bottom of the sections gives two surfaces: Top (finished grade) and Datum (the bottom of the pavement, for earthwork).

A corridor is built from four things: an alignment, its design profile, an assembly and a ground surface. Change any of them — drag a PI, move a PVI, widen a lane, re-survey the ground — and the corridor rebuilds by itself, followed by its surfaces, sample lines and volumes.

All the tools are on the Roads ribbon tab, in the Corridor group, and on the command line (see the Roads commands). Typical Section and Corridor open a dialog with every choice filled in; the typed commands ask the same questions one prompt at a time. Each command or dialog is one undo step.

The pictures use the sample project (Help ▸ Open the Sample Project): the Teresa Bypass Road, Km 35+200 to Km 36+422.77, with the typical section DPWH National Secondary, PCCP and the corridor Teresa Bypass Corridor. Point labels and TIN lines are turned off to keep the plan clear.

Making a typical section

Start with a typical section from the design standard: Terrace fills in the lane and shoulder widths, the crown and shoulder slopes and the cut and fill slopes of the road class, so a DPWH section is right the first time. You can change every value afterwards.

1. Click Roads ▸ Typical Section (or Choose a typical section in Next step). The Typical Section dialog opens.
2. Under Section, pick Two-lane rural (the default), Urban (curb, sidewalk) or Divided (median).
3. Under Road class, pick the class from the project's standard. Terrace starts with the road class of the selected (or first) alignment; when no alignment has one, it takes the class whose rolling-terrain design speed is closest to 60 km/h (DPWH National Secondary). The line under the menu shows what that class gives: for National Secondary, Lanes 3.35 m at 1.5%, shoulders 2.5 m at 3%, cut 1.5:1, fill 1.5:1.
4. Leave Name empty for an automatic name made from the kind and class, such as Two-lane rural (National Secondary), or type your own.
5. Click Create.

Terrace makes the assembly and draws it beside the project, to the left of everything already drawn (you don't click a place). The command history and a short message say what was made, for example Typical section Urban (National Secondary): 8 parts. The assembly is drawn on the C-ROAD-ASSM layer at its baseline point, with its name under it, and is listed under Assemblies in the Project browser. Rename it in Properties at any time.

From the command line

Type CREATEASSEMBLY (CASSEMBLY, or TYPICALSECTION) to make the section by prompts and place it where you click.

1. Terrace asks Typical section for National Secondary [Rural/Urban/Divided/Class/Dialog] <Rural>. The road class in the prompt is the one of your latest alignment that has one; with none, it's DPWH National Secondary (AASHTO: Rural Collector). Press Enter for a two-lane rural road, or type U (urban) or D (divided). Type DI to close the command and open the Typical Section dialog instead.
2. To use another road class, type C first: Terrace lists the standard's classes in the command history and asks Road class. Type the name or its first letters (prov for Provincial) and press Enter; then choose rural, urban or divided.
3. At Specify assembly location (baseline point), move the cursor: the section's shape follows it. Click where you want it drawn — beside the plan, out of the way.

Terrace lists the new assembly's parts in the command history, with each lane's width and slope:

The three kinds

What comes from the road class: lane width, shoulder width, cross slope of the lanes (falling away from the crown), shoulder slope, and the cut and fill slopes. What comes from the standard: the pavement. A DPWH section gets 230 mm Portland cement concrete pavement (PCCP) on 200 mm aggregate subbase (DPWH Items 311 and 200); an AASHTO section gets two 50 mm asphalt layers on 150 mm base and 200 mm subbase.

These are the built-in values; your project's standard may differ if someone edited it (see Standards and styles). Side slopes are written run:rise, so 1.5:1 is 1.5 m across for every 1 m up or down.

Changing a typical section

Select the assembly — click its drawing, or its name in the Project browser — and the Properties panel lists every part with its values, one group per part. Change a value and press Enter: the assembly redraws and every corridor built with it rebuilds. Each change is one undo step.

At the top are Name, Description, Style and the number of Parts. Then each part, titled with its number, name and side (1. Lane Right (right)). The rows depend on the part's kind:

• Lengths (widths, depths, offsets) in project units, such as Width 3.35 m.
• Slopes and grades in percent, measured going outward from the attachment point: −1.5 % falls away from the road, +2 % rises.
• Side slope ratios as (run : 1): 1.5 means 1.5:1.
• Choices, such as Superelevation (lane or none).
• Switches, such as Paved on a shoulder.
• Text, such as the material names used for quantities (Pave1 material: Portland Cement Concrete Pavement).

What each value means is in the catalog below. Use the search box at the top of the panel to find a row quickly (type cut to see every cut slope).

Adding a part

To add a barrier, a ditch, a wall or any other part, use ADDSUBASSEMBLY (SUBASSEMBLY), on Roads ▸ Add Subassembly.

1. At Select assembly, press Enter for the selected (or latest) assembly, click another one, or type its name.
2. At Subassembly kind (? for the list), type the kind, such as BarrierJersey. The first letters are enough (DitchV), and case doesn't matter. Type ? (or press Enter) to list every kind by category. Terrace prints the kind's description.
3. At Side [Right/Left/Both/None], press Enter for both sides, or type R or L. N (the default for medians) centers the part on the baseline point.

The new part is attached to the outermost part on that side and named after its kind and side (GuardrailBlock Right):

The subassembly catalog

Every part is one of 23 kinds. All of them follow the same rules: they're built outward from the point they're attached to (to the right for right parts, to the left for left parts); "slope" values are rise/run going outward; "ratio" values are side slopes run:rise. Parts with layers make shapes (pavement, base, subbase, curb…) that are measured for quantities; the material text of each shape names the pay item (see DPWH pay items).

The defaults above are the catalog's; parts made by CREATEASSEMBLY take their widths, slopes and pavement from the road class and standard instead. The daylight kinds and the wall have a Surface switch that the corridor's target sets for you, MaxRun (how far out to look for the ground) and FallbackRun (how far the fill slope is drawn when there's no ground to reach).

Building the corridor

Once the road has a design profile and a typical section, build the corridor. Terrace fills in the obvious answer for every choice, so on a simple project it's one click on Create.

1. Click Roads ▸ Corridor (or Build the corridor in Next step). It's also on the Alignment contextual tab when a centerline is selected. The New Corridor dialog opens on the selected alignment (or the one the selected profile or profile view belongs to; else the first).
2. Check the fields (table below) and change what you need.
3. Click Create.

Terrace builds the corridor at once and says how many sections it has, for example Corridor Road 1: 204 sections. (with the number of notes, if some sections had a problem). Create refuses, with a note at the bottom of the dialog, when the alignment has no design profile, there's no typical section yet, or the name is empty or already used.

From the command line

Type CREATECORRIDOR (CCORRIDOR, or CORRIDOR) to answer the same questions one prompt at a time; Enter takes each default, so it's the command and five presses of Enter.

1. Select baseline alignment [Dialog]: Enter for the selected (or latest) alignment, or click one, or type its name. Type D to open the New Corridor dialog instead. If the alignment has no design profile yet, Terrace says so and stops — draw one first with DRAWPROFILE (see Profiles).
2. Select design profile: Enter for the alignment's design profile. A profile of another alignment is refused.
3. Select assembly: Enter for the selected (or latest) typical section. With no assembly at all, Terrace asks you to make one first.
4. Select target surface for daylighting [None]: Enter for the existing ground (the surface called EG or Existing…, else the first surface that isn't a corridor's). Type N for none: side slopes are then drawn a fixed distance (FallbackRun).
5. Section frequency on tangents (half on curves): Enter for 10 m (25 ft in US units), or type another distance.

The command always makes both the Top and the Datum surface.

What you get:

• A corridor named Road 1 (Road 2… for the next ones; rename it in Properties) with one baseline and one region, Region 1. Sections are built from the start to the end of the design profile within the alignment.
• Sections every 10 m on tangents and every 5 m on curves, spirals and vertical curves, plus one at every geometry point (TS, SC, PC, PVI…) and every superelevation change.
• Feature lines along the section points, drawn on C-ROAD-CORR, and the section lines on C-ROAD-CORR-SCTN.
• Two new surfaces, Road 1 Top and Road 1 Datum (those you ticked, in the dialog), listed under Surfaces.
• A summary in the command history; and, if some sections had a problem, up to six notes such as daylight not reaching the ground, with the rest in Properties.

Daylighting and targets

A target is another object a part follows. When you choose a daylight surface, the New Corridor dialog (and CREATECORRIDOR) makes every part that can reach a surface — the side slopes, DaylightGeneral, LinkSlopeToSurface, the retaining wall — target that surface. At each section Terrace then:

• decides whether the section is in cut or fill at the hinge (the outer edge of the shoulder);
• in fill, runs the fill slope down until it meets the ground; in cut, builds the ditch (for BasicSideSlopeCutDitch) and runs the cut slope up to the ground;
• for DaylightGeneral, picks the slope by depth — flatter for shallow cuts and fills, steeper for deep ones — and adds benches every CutBenchHeight / FillBenchHeight if you set them;
• gives up after MaxRun (200 m) and writes a note naming the station and side.

The point where the slope meets the ground is coded Daylight (and Daylight_Cut or Daylight_Fill), so it becomes a feature line in plan and a row in the slope stake report.

Superelevation in the corridor

You don't set superelevation in the corridor: it comes from the alignment. When the alignment has superelevation (computed from the standard's e_max and the design speed — see Alignments), each lane whose Superelevation is lane takes the cross slope of its side at every station: normal crown on tangents, rotating through the runout and runoff, full superelevation on the curve.

Shoulders follow one of three rules (their Superelevation row):

• breakover (the default): on the low side of the curve the shoulder is never flatter than the lane; on the high side it keeps its own slope as long as the difference from the lane (the rollover) stays within MaxBreakover, 8 %.
• lane: the shoulder takes the lane's slope.
• none: the shoulder keeps its own Slope.

Set a lane to none to keep its own Slope everywhere (a one-way ramp lane, for instance). Because each region adds a section at every superelevation change (At superelevation points), the transitions are modelled exactly, not just at the 5 m and 10 m stations.

Corridor properties

Select the corridor in the plan or the Project browser. The Corridor contextual tab appears on the ribbon (Rebuild, Sample Lines, Volumes, and Properties, Zoom To, Report), and the Properties panel shows:

Below the rows, the panel lists the corridor's problems in plain words (for example daylight that didn't reach the ground at a station), each with Zoom to. The Project browser shows a green dot for an up-to-date corridor, and another colour when it's waiting for a rebuild or has problems.

Rebuilding

Normally you never rebuild by hand: after each command Terrace rebuilds what changed and everything downstream, and the status bar says what it did (Updated 3 objects, redraw 3 in 12 ms). Rebuild yourself when:

• the corridor's Rebuild by itself is off: click Rebuild in Properties or on the Corridor tab, or type CIVILREBUILD (CRB) with the corridor selected;
• you want everything brought up to date at once: CIVILUPDATE (CUP), also Sheets ▸ Update Now.

See Selecting and editing for how live updates work.

Intersections

Terrace's corridor engine knows how to build an intersection of two roads — curb return alignments and profiles, and regions split so the crossing is built from the main road's crown and the side road's edge — but this version has no command or dialog for it, and the New Corridor dialog and CREATECORRIDOR make a corridor with a single baseline. For now, model an intersection with:

• a corridor for each road;
• curb returns drawn with CURBRETURN (Roads ▸ Curb Return, see Alignments);
• the corner areas graded with feature lines (see Grading).

The slope stake report

Slope stakes are what the survey crew sets out: at each station, the offset and elevation of the edge of pavement, the shoulder and the catch point where the slope meets the ground. Select the corridor and click Report… in Properties (or Corridor ▸ Report); the Reports dialog opens on Slope stakes.

Each row is one point: Station, Side (Left, Right or CL), Code, Offset from the centerline, Elevation, From CL (height above + or below − the centerline point) and the point's Northing and Easting. The codes reported are ETW (edge of travelled way), EPS (edge of paved shoulder), ESS (edge of subgrade shoulder), Hinge and Daylight (with Daylight_Cut / Daylight_Fill). Save it with Save CSV… or Save PDF…, or Copy it; see Reports for everything the dialog does.