Friday, 17 June 2011

Create a Corridor with a 90 Degree Bend

It is possible to create a corridor with a 90 degree bend without using outside curves.

A corridor with two 90 degree bends

The trick is to put very small arcs at the corners of your centreline alignment, and add a corridor frequency point to the midpoint of the arc.

My steps to create 90 degree bend in corridor.

1. create the centreline with a polyline and offset either side to create edge polylines

2. convert the 3 polylines into alignments (in the attached screen captures the alignments are CL, LHS Edge Bitument, RHS Edge Bitumen.

Centreline Alignment Geometry

 3. Create a 0.001 meter radius curve at each 90 deg bend on the centreline alignment

4. Create the profiles for the  centreline.

5. Create a corridor using the Centreline Alignment

6. Target the lane edges to the outside alignments

Corridor Properties showning regions
7. Split the corridor, using the split region command, into seperate rtegions, one region o end before the inside corner, (split at 44.69 in the attached images), with the next region to end after the inside corner - as it relates to the centreline alignment. (about 57 in the attached images. Except in the images i carried the region around past the next bend to end at 76.53 as the corridor has two 90 degree bends next to each other)

Corridor Frequency settings

8. In the corridor properties, set the frequency of the middle region, the one that goes around the bend, greater than the length of the region, and set the horizontal geometry point, superelevation critical points, profile geomtry points, profile high/low points and offset target geometry to No.

9. Add a frequency station to the corridor at the middle of the arc at the bend in the centreline alignment, (in the attached images, i added one at the middle of arcs for both bends in the alignment. I also added one just after the first bend and one just before the second bend to straighten up the curb. giving me 4 frequency stations for the middle region)

The corridor I created has a kerb and gutter with batter, so at the corners, the corridor featurelines outside the offset targets get narrowed due to the angle of the frequency line at the corner.

If you need a nicer look for the featurelines on the inside of the bends beyond the offset alignment targets, you can go into the corridor section editor and remove the subassemblies on the inside that would lie beyond the offset targets at the corner and have additional frequency stations closer to the inside corner.

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