Model roadway intersections

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In this segment,

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we will look at some of the tools

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and methods for modeling intersections between corridors.

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The first intersection that we will look at is a T intersection.

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So to make space for the intersection,

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we will turn off the center regions of the corridors that we previously created.

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And we also can adjust the limits

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in the corridor parameters or we can actually use

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the region grips to adjust the limits manually.

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So to provide the space to work in,

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we will adjust all three legs of this intersection.

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So to begin, we will select the intersection,

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drop down and choose create intersection.

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We choose the location of the intersection and we

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need to make sure that our alignments do intersect

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in the dialog box. We can provide the name of the corridor

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and how the roadways interact either with all

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crowns or with a primary alignment crown.

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And here we can choose the primary alignment as the east west alignment.

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Next,

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we can specify the offset parameters and we can provide the input values for

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the offsets or use an alignment to control the limits of the pavement.

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Here, we will specify the width for both sides of the roadway,

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then we specify the turning movement geometry

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or the curb radius

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and then we can input the assemblies for the segments.

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We can either use the default assemblies or we can

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specify the assemblies that we may have already created.

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We can either add this corridor to an existing corridor or

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we can create a separate intersection corridor and

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that's the option we'll choose for now.

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So once the intersection has been built, we can inspect for any issues here.

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It looks like the assembly that we chose may have some issues with it

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or we may need to update some of the targets.

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So anytime we change the assembly within the parameters,

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the targets are reset. In this case,

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we use the assembly that we created without target widths and offsets

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because we know that will match the corridor that we created previously.

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So once the intersection is correct and it lines up with our proposed design,

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we can adjust the regions again

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to close any gaps

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if needed.

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We can also revise the assemblies that

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were created with the intersection corridor.

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Here, we want to add a sidewalk to the curb and gutter return.

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Once we make any changes to the assemblies, we simply rebuild the corridor

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and then view the results

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for the next corridor.

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We have crossing alignments with a four legged intersection.

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We also have a turn lane from the northbound lane to the eastbound lanes

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that we want to include within the corridor,

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we follow the same steps by choosing the intersection command

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and specifying the intersection location

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for four legged intersections. We need to also specify the primary alignments.

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And here we'll choose the south alignment movement.

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We follow the same steps by providing the offset values or control alignments.

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And in this intersection,

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we have different values for the curve radius. In each quadrant,

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we can measure the radius from our

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C

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ad file as the input values.

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We also want to include a turn lane

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in the second quadrant

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and civil treaty allows us to choose the lane width,

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the curb radius,

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the taper length and the length of the

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turn lane in the decelerating and accelerating movements,

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then we can change the cross slope if needed.

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But for now, we'll keep the default values as they are

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for the assemblies. In this case, we'll choose the default settings

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and make any kind of modifications later.

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Once the corridor is complete, we can view the results.

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And here we see that the turn lanes were added nicely.

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If we needed to update the lane layouts, we could adjust the control alignments.

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We can also easily add or remove subassembly items

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in the assemblies,

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then rebuild the corridor.

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We can also make other revisions to the corridor parameters

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just as we have done previously with other corridors.

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In cases where we want more control of the intersection, we can use the manual method

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that utilizes offset alignments or features.

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So for this T intersection,

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we want to begin by modifying the primary corridor regions

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at the intersection. We only want to model half of the road

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and we can simply copy the main assembly

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and remove the lane and shoulder elements from 1.5.

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We then update the parameters with the new assembly

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and rerun the corridor.

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And now we have enough room that we can model

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the intersection exactly the way that we need to.

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So

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we need to create offset alignments that we can use as control for

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the horizontal and vertical location of the curb or edge of pavement lines.

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Now, here we'll choose the alignment

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to offset and

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specify the station limits

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and we can base this off of the other corridor regions

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or we can actually measure this in our file.

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Then we set the side to offset our control alignment.

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And in this case, we only want to offset to the right side.

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So we'll set the left side to zero.

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We need to specify the offset distance as well.

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In this particular instance, we need to set that distance at 32 ft.

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That's the distance from our center line

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to our lip of curb.

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Now, we want to be sure that we choose the profile

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and we can determine the offset slope

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and this will be set at the standard 2% slope.

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We will do the same thing for the approach roadway as well.

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We'll set the side at the distance

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at the station limits

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and then we'll offset that alignment on both sides

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one more step before we get into the corridor is to create a connected alignment.

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This will tie the offset alignments together as a single control.

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And it will also utilize the profile from each of those offset alignments.

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Then here we determine the offset alignments that we

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want to utilize and the radius between those alignments.

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So the profile is copied from those offset alignments

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but then interpolated between the two through our curve.

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And so this will be the control for our curb and gutter return.

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We will then create the assembly for this control line

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and it will be a simple assembly with

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one lane that will target the primary alignments.

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And on the right side of the assembly, we will add

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the curb and gutter and the sidewalk.

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Now we'll choose the approach corridor and add a baseline for the two curb returns

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and we'll specify the profile

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and the assembly. In this case, it's the assembly called that we called curb return

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and the station limits.

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And we will identify those in our file

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and we want to tighten the frequency

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and model along the curve.

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Then we can identify the target surface and

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pick the alignments to control the pavement width.

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And here we'll pick both the primary and the approach alignment

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as well as the primary and approach profile.

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Then we'll run

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that corridor and then inspect it

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and that looks like how we want it to turn out for our intersection. So

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we'll do the same thing on the other side.

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And then again, we'll adjust the regions to close any gaps.

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And then we'll view the results using the section viewer.

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So in the section viewer, we can see

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the specified corridor

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and that looks to be correct. So keep in mind when we set up all these corridors,

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we have the option to make them all

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part of the same corridor using multiple baselines.

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But in this case, we broke them up into separate corridors.

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The last type of intersection that we'll look at is a roundabout.

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And we have a tool that will lay this out for us fairly quickly.

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So we'll pick the intersections from the drop down,

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then select roundabout

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and Civil 3d provides several different country standards for roundabouts.

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Our design values will be initially based on those standards that we select

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so we can control the inner and outer circle diameters of our roundabout

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as well as the number of lanes and the existing surface.

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So once we place the center

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of the roundabout in our drawing,

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we can pick the alignments that connect to it.

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So with each leg of the roundabout, we can specify the median width

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and the lane width.

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Each time we add a leg, we want to inspect that

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to make sure that it matches our proposed line work.

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Then once we have all of our legs set

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the roundabout surface and corridor are created.

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So this gives us a general overview regarding

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how to model intersections with better precision.