Mastering AutoCAD® Civil 3D® 2010

CREATING A CORRIDOR WITH A LANE WIDENING 423

Creating a Corridor with a Lane Widening

So far, all of the corridor examples you looked at have a constant cross section. In the next section,

you take a look at what happens when a portion of your corridor needs to transition to a wider

section and then transition back to normal.

Using Target Alignments

Earlier in this chapter, we discussed baselines and mentioned that baselines can be broken up into

different regions. Regions are examined in detail in Chapter 12.

In this section, you apply another corridor parameter called a target. We mentioned the idea of

targets when you added a surface target for a daylighting subassembly. In addition to surfaces,

alignments and profiles can b e used as targets.

Many subassemblies have been programmed to allow for not only a baseline attachment point

but also additional attachment points o n target alignments and/or profiles. Figure 11.42 shows a

centerline alignment to be used as a baseline and an edge-of-travel way alignment to be used as

a target.

Figure 11.42

A centerline alignment

used as a baseline and

an edge-of-travel way

alignment used as a

target

The subassembly will be stretched, raised, lowered, and adjusted to reflect the location and

elevation of the target. In this chapter, we discuss target alignments. In Chapter 12, we go into

more detail about using profile targets.

For example, the BasicLaneTransition subassembly can be set up to hook onto an alignment

and a profile. Think of the lane as a rubber band that is attached both to the baseline of the corri-

dor (such as the road centerline) and the target alignment. As the target alignment, such as a lane

widening, gets further from the baseline, the rubber band is stretched wider. As that target align-

ment transitions back toward the baseline, the rubber band changes to reflect a narrower cross

section. Figure 11.43 shows a corridor built using the edge-of-travel way alignment previously

shown in Figure 11.42 as a target.

Figure 11.43

A corridor built using

the centerline and

the edge-of-travel way

alignments

As discussed in Chapter 10, the BasicLaneTransition subassembly has several options for how

it will transition. For the next example, you use Hold Grade, Change Offset. Hold Grade means

the subassembly will hold the default grade of −2 percent as it is stretched to change offset with

424 CHAPTER 11 EASY DOES IT: BASIC CORRIDORS

the target alignment. Using t he Hold Grade, Change Offset setting eliminates the need for a target

profile, because the elevation at the edge-of-travel way will be determined by the default grade

(−2 percent, in this case) and lane width at a given sampling location.

The following exercise teaches you how to use a transition alignment as a corridor target for a

lane widening:

1. Open the Corridor Widening.dwg file. Note that this drawing has a corridor.

2. Freeze the layer C-ROAD-CORR. Note that the Widening EOP alignment represents the

edge-of-pavement for a street parking zone.

3. Thaw the layer C-ROAD-CORR.

4. Pan over to the assembly in the drawing. Select the right lane subassembly and choose

Subassembly Properties from the Modify Subassembly palette. Switch to t he Parameters

tab on the Subassembly Properties dialog.

5. Note that the entry for the Transition field is Hold Grade, Change Offset, as shown in

Figure 11.44. Click OK to dismiss the dialog.

Figure 11.44

Set the Default

Input Value for the

Transition field to Hold

Grade, Change Offset

6. Pan over to your corridor. Pick the corridor and choose Corridor Properties from the

Modify panel. Switch to the Parameters tab on the Corridor Properties dialog.

7. Click Set All Targets. The Target Mapping dialog opens. Click in the field next to Width

or Offset Targets to bring up the Set Width or Offset Target dialog.

8. In the Set Width or Offset Target Dialog, select the Widening EOP alignment, and then

click the Add button. The Widening EOP alignment will appear in the lower portion of

the dialog.

9. Click OK to dismiss the dialog. Click OK again to dismiss the Target Mapping dialog, and

then click OK once more to dismiss the Corridor Properties dialog.