Troubleshooting Cul-de-Sacs

Did you know that in French, the literal meaning of cul-de-sac is "bottom of the bag." Did you also know that "cul-de-sac" is Quebecois slang for the seat of your pants? I'm not making that up - some clients in Montreal told me that.

So. Civil 3D can make great cul-de-sacs if you know what you are doing. This post does not teach you how to make them, rather I'd like to discuss some common things that can go wrong.

Situation #1: The Cone to China

This is what it looks like in plan view with contours turned on. In my designs, I like to whip the alignment around 180 degrees (to avoid situations 2 and 3).

So the glob of contours is happening right where my north EOP (Edge of Pavement) alignment is supposed to touch my south EOP alignment.




And this second picture is what is going on with the surface model in the Object viewer. YUCK.

Why does this happen? Stationing somewhere is not perfect. Your profiles' stations must end EXACTLY at your alignments' end stations for the EOP's. Also the EOP's must meet exactly with not so much as a hairline gap.









Situation #2: The Gap

It not just a place for mediocre pants anymore.

In object viewer you may be lulled into a false sense of security with this one. At first glance, the surface model looks just fine.

What has happened in this situation is the end of alignment is not centered exactly inside the circular portion of the cul-de-sac.

In this case, it is slightly inside of the angled segment of the alignment. The corridor parameters tell the assembly to look for the main centerline as a width target. The base line is the EOP. When assemblies get applied at each frequency line, they shoot out perpendicularly to find their target. If the target alignment is out of whack, the assemblies miss the target and give up. The width they actually are is how the assembly was drawn- no stretching happens.

Situation #3: Don't Be Too Obtuse

In this situation we see the same cul-de-sac, except the off-center end of the alignment is slightly outside the angle of the alignment.
The assemblies overshoot the Alignment endpoint they should be hitting, and reconnect with their target in the wrong spot.





The lesson you should take away, here, is that corridors only do what they are told. You need to make sure your stations line up on your baseline's alignment and profile. You need to make sure the endpoint of the alignment is exactly in the center (unless you use my world-famous button-hook method - blogging soon). Too long or too short of a target alignment will give you problems and, as shown above, left or right of the center of the cul-de-sac will also goof you up.

Good luck!